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RF interference

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scott-p(at)texas.net
Guest

Posted: Thu Dec 16, 2010 3:09 am Post subject: RF interference

Hi All,



I am aware this has been discussed before, but as the problem now 

effects my own airplane, I have am a bit more attentive...



I have a Yak 55M with an auto-plug conversion. The conversion has been 

in place for about 3 years now (roughly 400 hours). I am now getting RF 

interference picked up in the Briz radio from the mags/plug wires. At 

least I assume that is the source, as it is RPM dependent. It has been 

present since installation, but has been gradually getting worse over 

the past year or so. I assume that there is a shielding issue either at 

the mag connection or along the wires somewhere. My question to you is 

where should I start to look at trouble shooting this issue, and how do 

I go about fixing it (shy of completely replacing the plug wires, which 

I'd prefer not to do... But will do if need be...)?



Any thoughts you might have on the matter would be appreciated.



Thanks,



Scott Poehlmann

Yak 55M N155YK

radiopicture

Joined: 23 Jun 2008
Posts: 263

Posted: Thu Dec 16, 2010 4:07 am Post subject: RF interference

Could the tach generator be an issue?



Also wondering if the dielectric properties of the plug wires are  

changing due to long term heat exposure.

On Dec 16, 2010, at 6:06 AM, Scott Poehlmann wrote:



 	  Quote: 	
		   



 Hi All,



 I am aware this has been discussed before, but as the problem now  

 effects my own airplane, I have am a bit more attentive...



 I have a Yak 55M with an auto-plug conversion. The conversion has  

 been in place for about 3 years now (roughly 400 hours). I am now  

 getting RF interference picked up in the Briz radio from the mags/ 

 plug wires. At least I assume that is the source, as it is RPM  

 dependent. It has been present since installation, but has been  

 gradually getting worse over the past year or so. I assume that  

 there is a shielding issue either at the mag connection or along the  

 wires somewhere. My question to you is where should I start to look  

 at trouble shooting this issue, and how do I go about fixing it (shy  

 of completely replacing the plug wires, which I'd prefer not to  

 do... But will do if need be...)?



 Any thoughts you might have on the matter would be appreciated.



 Thanks,



 Scott Poehlmann

 Yak 55M N155YK

pa3arw(at)euronet.nl
Guest

Posted: Thu Dec 16, 2010 4:11 am Post subject: RF interference

Scott,



This is one of the most difficult things to find/resolve.

A couple of possibilities:

How did you determine it is RF interference, i.e. is it picked up by the

antenna or via the power line?? Is the interference opening the squelch?

This can easily be checked by disconnecting the antenna and connecting a

small 50 Ohm dummyload.

If it is picked up by the antenna it will be a real problem to resolve

(assuming all the shielding of the plugs wiring etc is OK), not to say

almost impossible without redesigning the radio w.r.t. grounding, internal

decoupling etc.



If it is picked up on the power leads it is easier to prevent by using a

filter in the powerline. Ask Dennis for contact details of a company, I

think in Texas, who makes those filters suitable for use in aeroplanes.



The interesting thing y're saying however is "it got worse over time" if

that is the case I would check the shielding of the RPM-generator first. If,

over time, the shielding has been damaged you can be sure it will generate a

lot of noise on the radio which increases or decreases with the rpm.



Hope this will help you a little.



Hans Oortman

RA3326K

Netherlands



-----Oorspronkelijk bericht-----

Van: owner-yak-list-server(at)matronics.com

[mailto:owner-yak-list-server(at)matronics.com] Namens Scott Poehlmann

Verzonden: donderdag 16 december 2010 12:07

Aan: yak-list(at)matronics.com

Onderwerp: RF interference






Hi All,



I am aware this has been discussed before, but as the problem now 

effects my own airplane, I have am a bit more attentive...



I have a Yak 55M with an auto-plug conversion. The conversion has been 

in place for about 3 years now (roughly 400 hours). I am now getting RF 

interference picked up in the Briz radio from the mags/plug wires. At 

least I assume that is the source, as it is RPM dependent. It has been 

present since installation, but has been gradually getting worse over 

the past year or so. I assume that there is a shielding issue either at 

the mag connection or along the wires somewhere. My question to you is 

where should I start to look at trouble shooting this issue, and how do 

I go about fixing it (shy of completely replacing the plug wires, which 

I'd prefer not to do... But will do if need be...)?



Any thoughts you might have on the matter would be appreciated.



Thanks,



Scott Poehlmann

Yak 55M N155YK

dsavarese0812(at)bellsout
Guest

Posted: Thu Dec 16, 2010 5:34 am Post subject: RF interference

We have installed these magneto filters on the P-leads 

http://www.aircraftspruce.com/catalog/elpages/lsMagFilter.php, mounting 

them on one of the studs of the round accessory case cover.  They have 

worked quite well and are easily installed by removing the P lead and 

de-soldering the shield and wire from the P-lead "button", installing a 

terminal lung on the P lead wire and connecting it to the mag filter.  

Then install a terminal lug on the mag filter wire and soldering it to 

the P-lead button.



For additional noise attenuation, we have also installed this noise 

filter directly on the DC line to the affected unit.  

http://www.aircraftspruce.com/catalog/elpages/lsStrobeNoiseEl.php.  

There are larger noise filters with higher current ratings that could be 

used on the DC bus.  

http://www.aircraftspruce.com/catalog/elpages/lonestarFilter70amp.php.

Dennis



On 12/16/2010 6:09 AM, Hans Oortman wrote:

 	  Quote: 	
		   



 Scott,



 This is one of the most difficult things to find/resolve.

 A couple of possibilities:

 How did you determine it is RF interference, i.e. is it picked up by the

 antenna or via the power line?? Is the interference opening the squelch?

 This can easily be checked by disconnecting the antenna and connecting a

 small 50 Ohm dummyload.

 If it is picked up by the antenna it will be a real problem to resolve

 (assuming all the shielding of the plugs wiring etc is OK), not to say

 almost impossible without redesigning the radio w.r.t. grounding, internal

 decoupling etc.



 If it is picked up on the power leads it is easier to prevent by using a

 filter in the powerline. Ask Dennis for contact details of a company, I

 think in Texas, who makes those filters suitable for use in aeroplanes.



 The interesting thing y're saying however is "it got worse over time" if

 that is the case I would check the shielding of the RPM-generator first. If,

 over time, the shielding has been damaged you can be sure it will generate a

 lot of noise on the radio which increases or decreases with the rpm.



 Hope this will help you a little.



 Hans Oortman

 RA3326K

 Netherlands



 -----Oorspronkelijk bericht-----

 Van: owner-yak-list-server(at)matronics.com

 [mailto:owner-yak-list-server(at)matronics.com] Namens Scott Poehlmann

 Verzonden: donderdag 16 december 2010 12:07

 Aan: yak-list(at)matronics.com

 Onderwerp: RF interference



 



 Hi All,



 I am aware this has been discussed before, but as the problem now

 effects my own airplane, I have am a bit more attentive...



 I have a Yak 55M with an auto-plug conversion. The conversion has been

 in place for about 3 years now (roughly 400 hours). I am now getting RF

 interference picked up in the Briz radio from the mags/plug wires. At

 least I assume that is the source, as it is RPM dependent. It has been

 present since installation, but has been gradually getting worse over

 the past year or so. I assume that there is a shielding issue either at

 the mag connection or along the wires somewhere. My question to you is

 where should I start to look at trouble shooting this issue, and how do

 I go about fixing it (shy of completely replacing the plug wires, which

 I'd prefer not to do... But will do if need be...)?



 Any thoughts you might have on the matter would be appreciated.



 Thanks,



 Scott Poehlmann

 Yak 55M N155YK

viperdoc(at)mindspring.co
Guest

Posted: Thu Dec 16, 2010 10:39 am Post subject: RF interference

Check the shielding on your Tac Generator. That is the most likely source

for RPM related noise.

Doc



--

mikspin

Joined: 12 Aug 2007
Posts: 66

Posted: Fri Dec 17, 2010 1:47 am Post subject: Re: RF interference

Hans,



Where are you in the Netherlands?  I routinely overnight in Amsterdam.



(Sorry to go off topic here guys)



Mike Hastings

Yak 55M

(Oversee several Yak 52's)

mikspin

Joined: 12 Aug 2007
Posts: 66

Posted: Fri Dec 17, 2010 1:48 am Post subject: Re: RF interference

Scott,



Did you get those diagrams I emailed you a while back?



Mike

yakplt(at)yahoo.com
Guest

Posted: Fri Dec 17, 2010 9:22 am Post subject: RF interference

Do the following: 



Remove the plug from the Tach Gen and tie it back. Run the aircraft.  Does the noise go away?  Then it is indeed your Tach Gen and it is most likely shielding at the Tach Generator plug itself.  Be careful taking this plug apart as it is common for the soldering on these wires to break. 



If the noise does not go away, fly the airplane.  Over the airport come to complete idle and then shut the mags off.  Both mags, turn them off.  



You're now a glider.  



Did the noise go away?  If it did, then you have a MAG noise problem.  The mag noise filters will help, but before you go to that effort, look at the P leak plugs that go into the side of the mags.  It is very common for people to twist these plugs off during some kind of maint. action and in the process twist the shield right off the plug as well.  If the P Lead is unshielded you will have one huge amount of noise.  



If the noise is still there even when you have performed these steps (whcih is highly unlikely) then you've got some other device radiating energy in the aircraft.  Start turning everything that you can off to try and identify it.  



Suggestions have been made to see if it is coming in via the antenna or the power wiring.  I have posted these suggestions before, but it is something you do at the end of troubleshooting and not the beginning.  It is much easier to identify the noise source and eliminate it where it is coming from.  If you can't identify the noise and you are lucky enough to have it coming in via the power wires (again this is rare), a choke on the input power wiring can help eliminate the noise.  This can be as simple as a snap on torroid, or an expensive (purchased) filter, that is usually some sort of "Pi L brute force" filter consisting of two caps and an inductor.  Usually, snap on torroids are just as effective and much cheaper.  Again though, noise coming in via the power wiring is rare.  It usually is coming in via the antenna, and that means you MUST eliminate the noise at it's source.  



The tests described above will usually nail the problem in short order.  



Mark Bitterlich 



p.s.  The reason I recommend shutting the mags off at idle in flight versus doing it on the ground is because the engine keeps wind-milling even with the mags off, and you can leave them off much longer while you are listening for radio noise and seeing if it goes away.  Shutting the engine off with the mags and the engine windmilling with it at idle will not hurt anything, although the engine will cool off really fast, so when you turn the mags back on and the engine once again is actually "running", don't just cob the power to 100%.  Bring it in slowly.  Common sense applies.  



--- On Thu, 12/16/10, Roger Kemp M.D. <viperdoc(at)mindspring.com> wrote:



[quote] From: Roger Kemp M.D. <viperdoc(at)mindspring.com>

 Subject: RE: RF interference

 To: yak-list(at)matronics.com

 Date: Thursday, December 16, 2010, 1:35 PM

 

 "Roger Kemp M.D." <viperdoc(at)mindspring.com>

 

 Check the shielding on your Tac Generator. That is the most

 likely source

 for RPM related noise.

 Doc

 

 --

scott-p(at)texas.net
Guest

Posted: Fri Dec 17, 2010 6:07 pm Post subject: RF interference

Thanks Mark,

I knew that you would have a great, step by step method.

Went out to the hangar today: looks like the P-leads are the 

culprit--BOTH have the shielding detached from the connector and about 1 

cm of unshielded lead "hanging in the breeze". I'll spend some time 

tomorrow AM soldering the shielding to the connector (it appears that 

this has been done before and that the solder joints have failed...), 

and will advise if this doesn't fix the problem.

Now for the next question: any ideas where to find a cover for the tach 

generator drive? I am running a Horizon digital tach (which takes its 

data from the mag--in fact it is wired into the back of the mag 

switch...), and I have no tach generator, just a big open fitting with a 

drive (and seal) at the bottom... Threaded on the outside, of course.

Thanks again, and to everyone else who provided information. This list 

is a tremendous asset to the continued operation of these airplanes.

Scott

On 12-17-2010 10:15, Yak Pilot wrote:

[quote] 

 Do the following:

 Remove the plug from the Tach Gen and tie it back. Run the aircraft.  Does the noise go away?  Then it is indeed your Tach Gen and it is most likely shielding at the Tach Generator plug itself.  Be careful taking this plug apart as it is common for the soldering on these wires to break.

 If the noise does not go away, fly the airplane.  Over the airport come to complete idle and then shut the mags off.  Both mags, turn them off.

 You're now a glider.

 Did the noise go away?  If it did, then you have a MAG noise problem.  The mag noise filters will help, but before you go to that effort, look at the P leak plugs that go into the side of the mags.  It is very common for people to twist these plugs off during some kind of maint. action and in the process twist the shield right off the plug as well.  If the P Lead is unshielded you will have one huge amount of noise.

 If the noise is still there even when you have performed these steps (whcih is highly unlikely) then you've got some other device radiating energy in the aircraft.  Start turning everything that you can off to try and identify it.

 Suggestions have been made to see if it is coming in via the antenna or the power wiring.  I have posted these suggestions before, but it is something you do at the end of troubleshooting and not the beginning.  It is much easier to identify the noise source and eliminate it where it is coming from.  If you can't identify the noise and you are lucky enough to have it coming in via the power wires (again this is rare), a choke on the input power wiring can help eliminate the noise.  This can be as simple as a snap on torroid, or an expensive (purchased) filter, that is usually some sort of "Pi L brute force" filter consisting of two caps and an inductor.  Usually, snap on torroids are just as effective and much cheaper.  Again though, noise coming in via the power wiring is rare.  It usually is coming in via the antenna, and that means you MUST eliminate the noise at it's source.

 The tests described above will usually nail the problem in short order.

 Mark Bitterlich

 p.s.  The reason I recommend shutting the mags off at idle in flight versus doing it on the ground is because the engine keeps wind-milling even with the mags off, and you can leave them off much longer while you are listening for radio noise and seeing if it goes away.  Shutting the engine off with the mags and the engine windmilling with it at idle will not hurt anything, although the engine will cool off really fast, so when you turn the mags back on and the engine once again is actually "running", don't just cob the power to 100%.  Bring it in slowly.  Common sense applies.

 --- On Thu, 12/16/10, Roger Kemp M.D.<viperdoc(at)mindspring.com>  wrote:

> From: Roger Kemp M.D.<viperdoc(at)mindspring.com>

> Subject: RE: RF interference

> To: yak-list(at)matronics.com

> Date: Thursday, December 16, 2010, 1:35 PM

> 

> "Roger Kemp M.D."<viperdoc(at)mindspring.com>

>

> Check the shielding on your Tac Generator. That is the most

> likely source

> for RPM related noise.

> Doc

>

> --

yakplt(at)yahoo.com
Guest

Posted: Sat Dec 18, 2010 12:36 pm Post subject: RF interference

Hmmm!   

I need to add one step to my troubleshooting procedures Scott: 

Step Three:  Have you added a digital tach that takes it's input off the P Leads.  If so, that is very high potential for noise addition to your aircraft. 

I actually thought of mentioning that, but since you did not bring it up in your initial email, I guessed (incorrectly) that you had not modified anything since you put in the new spark plugs and wire kit.  

To answer your question:  When pulling the Tach Drive, most of the folks I know have had a plate made that bolts on with the four corner bolts to the plate and there you go.  You make it yourself.  You need to be very very careful here, because if you remove the wrong "plate" you also will expose the gearing for the tach drive that also is part of the air distributor drive.  What I am saying here is that if you pull the wrong plates and stuff in an attempt to put a new cover plate over the tach drive, you can easily disturb the gearing inside, which will in turn through your air start distributor out of adjustment and then you are DEEP KIMSHEE!  Re-timing the airstart distributor is NOT EASY regardless of what anyone might tell you otherwise.  So Scott, be very very careful of what you take apart in that area.  Without photo's it is hard for me to describe what to take off and what not to take off.  Talk to Dennis about tha

--- On Fri, 12/17/10, Scott Poehlmann <scott-p(at)texas.net> wrote:

[quote] From: Scott Poehlmann <scott-p(at)texas.net>

 Subject: Re: RF interference

 To: yak-list(at)matronics.com

 Date: Friday, December 17, 2010, 9:03 PM

 Scott Poehlmann <scott-p(at)texas.net>

 Thanks Mark,

 I knew that you would have a great, step by step method.

 Went out to the hangar today: looks like the P-leads are

 the 

 culprit--BOTH have the shielding detached from the

 connector and about 1 

 cm of unshielded lead "hanging in the breeze". I'll spend

 some time 

 tomorrow AM soldering the shielding to the connector (it

 appears that 

 this has been done before and that the solder joints have

 failed...), 

 and will advise if this doesn't fix the problem.

 Now for the next question: any ideas where to find a cover

 for the tach 

 generator drive? I am running a Horizon digital tach (which

 takes its 

 data from the mag--in fact it is wired into the back of the

 mag 

 switch...), and I have no tach generator, just a big open

 fitting with a 

 drive (and seal) at the bottom... Threaded on the outside,

 of course.

 Thanks again, and to everyone else who provided

 information. This list 

 is a tremendous asset to the continued operation of these

 airplanes.

 Scott

 On 12-17-2010 10:15, Yak Pilot wrote:

 > -->  Yak-List message posted by: Yak

 Pilot<yakplt(at)yahoo.com>

 >

 > Do the following:

 >

 > Remove the plug from the Tach Gen and tie it back. Run

 the aircraft.  Does the noise go away?  Then it is

 indeed your Tach Gen and it is most likely shielding at the

 Tach Generator plug itself.  Be careful taking this

 plug apart as it is common for the soldering on these wires

 to break.

 >

 > If the noise does not go away, fly the airplane. 

 Over the airport come to complete idle and then shut the

 mags off.  Both mags, turn them off.

 >

 > You're now a glider.

 >

 > Did the noise go away?  If it did, then you have

 a MAG noise problem.  The mag noise filters will help,

 but before you go to that effort, look at the P leak plugs

 that go into the side of the mags.  It is very common

 for people to twist these plugs off during some kind of

 maint. action and in the process twist the shield right off

 the plug as well.  If the P Lead is unshielded you will

 have one huge amount of noise.

 >

 > If the noise is still there even when you have

 performed these steps (whcih is highly unlikely) then you've

 got some other device radiating energy in the

 aircraft.  Start turning everything that you can off to

 try and identify it.

 >

 > Suggestions have been made to see if it is coming in

 via the antenna or the power wiring.  I have posted

 these suggestions before, but it is something you do at the

 end of troubleshooting and not the beginning.  It is

 much easier to identify the noise source and eliminate it

 where it is coming from.  If you can't identify the

 noise and you are lucky enough to have it coming in via the

 power wires (again this is rare), a choke on the input power

 wiring can help eliminate the noise.  This can be as

 simple as a snap on torroid, or an expensive (purchased)

 filter, that is usually some sort of "Pi L brute force"

 filter consisting of two caps and an inductor. 

 Usually, snap on torroids are just as effective and much

 cheaper.  Again though, noise coming in via the power

 wiring is rare.  It usually is coming in via the

 antenna, and that means you MUST eliminate the noise at it's

 source.

 >

 > The tests described above will usually nail the

 problem in short order.

 >

 > Mark Bitterlich

 >

 > p.s.  The reason I recommend shutting the mags

 off at idle in flight versus doing it on the ground is

 because the engine keeps wind-milling even with the mags

 off, and you can leave them off much longer while you are

 listening for radio noise and seeing if it goes away. 

 Shutting the engine off with the mags and the engine

 windmilling with it at idle will not hurt anything, although

 the engine will cool off really fast, so when you turn the

 mags back on and the engine once again is actually

 "running", don't just cob the power to 100%.  Bring it

 in slowly.  Common sense applies.

 >

 > --- On Thu, 12/16/10, Roger Kemp M.D.<viperdoc(at)mindspring.com> 

 wrote:

 >

 >> From: Roger Kemp M.D.<viperdoc(at)mindspring.com>

 >> Subject: RE: RF interference

 >> To: yak-list(at)matronics.com

 >> Date: Thursday, December 16, 2010, 1:35 PM

 >> -->  Yak-List message posted by:

 >> "Roger Kemp M.D."<viperdoc(at)mindspring.com>

 >>

 >> Check the shielding on your Tac Generator. That is

 the most

 >> likely source

 >> for RPM related noise.

 >> Doc

 >>

 >> --

yakplt(at)yahoo.com
Guest

Posted: Sat Dec 18, 2010 12:48 pm Post subject: RF interference

Hmmm!   

I need to add one step to my troubleshooting procedures Scott: 

Step Three:  Have you added a digital tach that takes it's input off the P Leads.  If so, that is very high potential for noise addition to your aircraft. 

I actually thought of mentioning that, but since you did not bring it up in your initial email, I guessed (incorrectly) that you had not modified anything since you put in the new spark plugs and wire kit.  

To answer your question:  When pulling the Tach Drive, most of the folks I know have had a plate made that bolts on with the four corner bolts to the plate and there you go.  You make it yourself.  You need to be very very careful here, because if you remove the wrong "plate" you also will expose the gearing for the tach drive that also is part of the air distributor drive.  What I am saying here is that if you pull the wrong plates and stuff in an attempt to put a new cover plate over the tach drive, you can easily disturb the gearing inside, which will in turn through your air start distributor out of adjustment and then you are DEEP KIMSHEE!  Re-timing the airstart distributor is NOT EASY regardless of what anyone might tell you otherwise.  So Scott, be very very careful of what you take apart in that area.  Without photo's it is hard for me to describe what to take off and what not to take off.  Talk to Dennis about that for details.  

Somehow I just managed to send this message when my fingers slipped on the keyboardâ€¦ oopsâ€¦ so here is the end of the message, sorry.  

Going back to your noise on your radios.  I hate to tell you this Scott, but those new digital tachs that attach to your P leads are a real source of radio noise.  This is the forth time I have had a person who installed that tach start talking about radio noise.  I also have personal experience with that thing myself.  

Given that your Tach Generator is now removed from the aircraft, and you have installed the Digital Tach that used your P leads for a input, I am 99.999% sure that your new radio noise is from the P leads.  Yes, you should repair the shields down at the MAGâ€™s and that will help.  But you also are going to have to go back to the wires that have been attached behind the mag switch and make darn sure that shielded wires were used there as well.  Just leaving a tiny bit of exposed wire (I.E. Where there is no shielding on the P leads) will allow that to act as an antenna and RADIATE NOISE all over the aircraft.  

In one aircraft I worked on (a Sukhoi 26) I had to replace all of that wiring to the digital tach, and then... get ready for thisâ€¦.. I had to make an actual BOX out of aluminum and enclose the whole tach inside that box (a Faraday Shield per se) and ground all that.  

So that is the downside of using that kind of Tach, I am sorry to have to say.  Itâ€™s a GREAT TACH, and I love the way it works, but since it uses the P leads, you have to really pay attention to your shielding.  There is usually no filter that can eliminate this kind of noise.  Spark noise is very broad spectrum and if you are anywhere in the near field from this noise, youâ€™re pretty much screwed.  

One trick that SOMETIMES helps:  Take a handheld VHF radio, remove the antenna and stick a paperclip into the center conductor of the antenna jack.  Hook headphones to the handheld radio.  Now start the aircraft and use the radio as a â€œtest wandâ€ and run it around the wiring to try and find the source.  This is not easy and takes some effort.  

Bottom line:  Your noise is coming from your P leads and new tach.  Good luck.  Merry Christmas. 

Mark Bitterlich

--- On Fri, 12/17/10, Scott Poehlmann <scott-p(at)texas.net> wrote:

[quote] From: Scott Poehlmann <scott-p(at)texas.net>

 Subject: Re: RF interference

 To: yak-list(at)matronics.com

 Date: Friday, December 17, 2010, 9:03 PM

 Scott Poehlmann <scott-p(at)texas.net>

 Thanks Mark,

 I knew that you would have a great, step by step method.

 Went out to the hangar today: looks like the P-leads are

 the 

 culprit--BOTH have the shielding detached from the

 connector and about 1 

 cm of unshielded lead "hanging in the breeze". I'll spend

 some time 

 tomorrow AM soldering the shielding to the connector (it

 appears that 

 this has been done before and that the solder joints have

 failed...), 

 and will advise if this doesn't fix the problem.

 Now for the next question: any ideas where to find a cover

 for the tach 

 generator drive? I am running a Horizon digital tach (which

 takes its 

 data from the mag--in fact it is wired into the back of the

 mag 

 switch...), and I have no tach generator, just a big open

 fitting with a 

 drive (and seal) at the bottom... Threaded on the outside,

 of course.

 Thanks again, and to everyone else who provided

 information. This list 

 is a tremendous asset to the continued operation of these

 airplanes.

 Scott

 On 12-17-2010 10:15, Yak Pilot wrote:

 > -->Â  Yak-List message posted by: Yak

 Pilot<yakplt(at)yahoo.com>

 >

 > Do the following:

 >

 > Remove the plug from the Tach Gen and tie it back. Run

 the aircraft.Â  Does the noise go away?Â  Then it is

 indeed your Tach Gen and it is most likely shielding at the

 Tach Generator plug itself.Â  Be careful taking this

 plug apart as it is common for the soldering on these wires

 to break.

 >

 > If the noise does not go away, fly the airplane.Â 

 Over the airport come to complete idle and then shut the

 mags off.Â  Both mags, turn them off.

 >

 > You're now a glider.

 >

 > Did the noise go away?Â  If it did, then you have

 a MAG noise problem.Â  The mag noise filters will help,

 but before you go to that effort, look at the P leak plugs

 that go into the side of the mags.Â  It is very common

 for people to twist these plugs off during some kind of

 maint. action and in the process twist the shield right off

 the plug as well.Â  If the P Lead is unshielded you will

 have one huge amount of noise.

 >

 > If the noise is still there even when you have

 performed these steps (whcih is highly unlikely) then you've

 got some other device radiating energy in the

 aircraft.Â  Start turning everything that you can off to

 try and identify it.

 >

 > Suggestions have been made to see if it is coming in

 via the antenna or the power wiring.Â  I have posted

 these suggestions before, but it is something you do at the

 end of troubleshooting and not the beginning.Â  It is

 much easier to identify the noise source and eliminate it

 where it is coming from.Â  If you can't identify the

 noise and you are lucky enough to have it coming in via the

 power wires (again this is rare), a choke on the input power

 wiring can help eliminate the noise.Â  This can be as

 simple as a snap on torroid, or an expensive (purchased)

 filter, that is usually some sort of "Pi L brute force"

 filter consisting of two caps and an inductor.Â 

 Usually, snap on torroids are just as effective and much

 cheaper.Â  Again though, noise coming in via the power

 wiring is rare.Â  It usually is coming in via the

 antenna, and that means you MUST eliminate the noise at it's

 source.

 >

 > The tests described above will usually nail the

 problem in short order.

 >

 > Mark Bitterlich

 >

 > p.s.Â  The reason I recommend shutting the mags

 off at idle in flight versus doing it on the ground is

 because the engine keeps wind-milling even with the mags

 off, and you can leave them off much longer while you are

 listening for radio noise and seeing if it goes away.Â 

 Shutting the engine off with the mags and the engine

 windmilling with it at idle will not hurt anything, although

 the engine will cool off really fast, so when you turn the

 mags back on and the engine once again is actually

 "running", don't just cob the power to 100%.Â  Bring it

 in slowly.Â  Common sense applies.

 >

 > --- On Thu, 12/16/10, Roger Kemp M.D.<viperdoc(at)mindspring.com>Â 

 wrote:

 >

 >> From: Roger Kemp M.D.<viperdoc(at)mindspring.com>

 >> Subject: RE: RF interference

 >> To: yak-list(at)matronics.com

 >> Date: Thursday, December 16, 2010, 1:35 PM

 >> -->Â  Yak-List message posted by:

 >> "Roger Kemp M.D."<viperdoc(at)mindspring.com>

 >>

 >> Check the shielding on your Tac Generator. That is

 the most

 >> likely source

 >> for RPM related noise.

 >> Doc

 >>

 >> --

scott-p(at)texas.net
Guest

Posted: Sat Dec 18, 2010 2:35 pm Post subject: RF interference

Thanks Mark,



I didn't mention the tach because, frankly, I didn't think about it. The 

tach appears to be wired at the mag switch, and and that cabling is 

unshielded. I don't know if that is at issue or not, but given what 

happened today, I think not...



Having said that, I am 98% certain I have found the problem. I soldered 

the shield back on the right (#1) mag and now I have the problem only 

when the left (#2) mag is operating (i.e., position "2" and "1+2"). I 

will repeat the process with the left mag tomorrow, and I suspect that I 

am done. I am not particularly happy with the quality of the solder 

joints (it is hard to solder in the engine bay...) have you had any 

experience with copper tape shielding? It seems like an obvious solution 

rather than trying to solder behind the engine...



I will take a photo of the location of the former tach generator (or at 

least what I think is the location...) and see what you think. Given 

that both Jill and George have pre-manufactured plates, I will likely 

get one from one of them and put that on.



Thanks again,



Scott



On 12-18-2010 13:33, Yak Pilot wrote:

[quote] 



 Hmmm!



 I need to add one step to my troubleshooting procedures Scott:



 Step Three:  Have you added a digital tach that takes it's input off the P Leads.  If so, that is very high potential for noise addition to your aircraft.



 I actually thought of mentioning that, but since you did not bring it up in your initial email, I guessed (incorrectly) that you had not modified anything since you put in the new spark plugs and wire kit.



 To answer your question:  When pulling the Tach Drive, most of the folks I know have had a plate made that bolts on with the four corner bolts to the plate and there you go.  You make it yourself.  You need to be very very careful here, because if you remove the wrong "plate" you also will expose the gearing for the tach drive that also is part of the air distributor drive.  What I am saying here is that if you pull the wrong plates and stuff in an attempt to put a new cover plate over the tach drive, you can easily disturb the gearing inside, which will in turn through your air start distributor out of adjustment and then you are DEEP KIMSHEE!  Re-timing the airstart distributor is NOT EASY regardless of what anyone might tell you otherwise.  So Scott, be very very careful of what you take apart in that area.  Without photo's it is hard for me to describe what to take off and what not to take off.  Talk to Dennis about tha



 --- On Fri, 12/17/10, Scott Poehlmann<scott-p(at)texas.net>  wrote:



> From: Scott Poehlmann<scott-p(at)texas.net>

> Subject: Re: RF interference

> To: yak-list(at)matronics.com

> Date: Friday, December 17, 2010, 9:03 PM

> 

> Scott Poehlmann<scott-p(at)texas.net>

>

> Thanks Mark,

>

> I knew that you would have a great, step by step method.

>

> Went out to the hangar today: looks like the P-leads are

> the

> culprit--BOTH have the shielding detached from the

> connector and about 1

> cm of unshielded lead "hanging in the breeze". I'll spend

> some time

> tomorrow AM soldering the shielding to the connector (it

> appears that

> this has been done before and that the solder joints have

> failed...),

> and will advise if this doesn't fix the problem.

>

> Now for the next question: any ideas where to find a cover

> for the tach

> generator drive? I am running a Horizon digital tach (which

> takes its

> data from the mag--in fact it is wired into the back of the

> mag

> switch...), and I have no tach generator, just a big open

> fitting with a

> drive (and seal) at the bottom... Threaded on the outside,

> of course.

>

> Thanks again, and to everyone else who provided

> information. This list

> is a tremendous asset to the continued operation of these

> airplanes.

>

> Scott

>

> On 12-17-2010 10:15, Yak Pilot wrote:

>> 

> Pilot<yakplt(at)yahoo.com>

>> Do the following:

>>

>> Remove the plug from the Tach Gen and tie it back. Run

> the aircraft.  Does the noise go away?  Then it is

> indeed your Tach Gen and it is most likely shielding at the

> Tach Generator plug itself.  Be careful taking this

> plug apart as it is common for the soldering on these wires

> to break.

>> If the noise does not go away, fly the airplane.

> Over the airport come to complete idle and then shut the

> mags off.  Both mags, turn them off.

>> You're now a glider.

>>

>> Did the noise go away?  If it did, then you have

> a MAG noise problem.  The mag noise filters will help,

> but before you go to that effort, look at the P leak plugs

> that go into the side of the mags.  It is very common

> for people to twist these plugs off during some kind of

> maint. action and in the process twist the shield right off

> the plug as well.  If the P Lead is unshielded you will

> have one huge amount of noise.

>> If the noise is still there even when you have

> performed these steps (whcih is highly unlikely) then you've

> got some other device radiating energy in the

> aircraft.  Start turning everything that you can off to

> try and identify it.

>> Suggestions have been made to see if it is coming in

> via the antenna or the power wiring.  I have posted

> these suggestions before, but it is something you do at the

> end of troubleshooting and not the beginning.  It is

> much easier to identify the noise source and eliminate it

> where it is coming from.  If you can't identify the

> noise and you are lucky enough to have it coming in via the

> power wires (again this is rare), a choke on the input power

> wiring can help eliminate the noise.  This can be as

> simple as a snap on torroid, or an expensive (purchased)

> filter, that is usually some sort of "Pi L brute force"

> filter consisting of two caps and an inductor. 

> Usually, snap on torroids are just as effective and much

> cheaper.  Again though, noise coming in via the power

> wiring is rare.  It usually is coming in via the

> antenna, and that means you MUST eliminate the noise at it's

> source.

>> The tests described above will usually nail the

> problem in short order.

>> Mark Bitterlich

>>

>> p.s.  The reason I recommend shutting the mags

> off at idle in flight versus doing it on the ground is

> because the engine keeps wind-milling even with the mags

> off, and you can leave them off much longer while you are

> listening for radio noise and seeing if it goes away. 

> Shutting the engine off with the mags and the engine

> windmilling with it at idle will not hurt anything, although

> the engine will cool off really fast, so when you turn the

> mags back on and the engine once again is actually

> "running", don't just cob the power to 100%.  Bring it

> in slowly.  Common sense applies.

>> --- On Thu, 12/16/10, Roger Kemp M.D.<viperdoc(at)mindspring.com>

> wrote:

>>> From: Roger Kemp M.D.<viperdoc(at)mindspring.com>

>>> Subject: RE: RF interference

>>> To: yak-list(at)matronics.com

>>> Date: Thursday, December 16, 2010, 1:35 PM

>>> 

>>> "Roger Kemp M.D."<viperdoc(at)mindspring.com>

>>>

>>> Check the shielding on your Tac Generator. That is

> the most

>>> likely source

>>> for RPM related noise.

>>> Doc

>>>

>>> --

scott-p(at)texas.net
Guest

Posted: Sat Dec 18, 2010 2:42 pm Post subject: RF interference

Ahh.

Perhaps I should shield the wires to the tach, too.  The interference 

really does go away to essentially nothing (ok, I get an occasional 

"pop" or two, but NOTHING like before) when running on just Mag 1 now, 

so if I can accomplish the same thing with Mag 2, then I am happy.

Will look into the shielding on those wires after fixing P-lead on Mag 

2, and report back.

Scott

On 12-18-2010 13:46, Yak Pilot wrote:

[quote] 

 Hmmm!

 I need to add one step to my troubleshooting procedures Scott:

 Step Three:  Have you added a digital tach that takes it's input off the P Leads.  If so, that is very high potential for noise addition to your aircraft.

 I actually thought of mentioning that, but since you did not bring it up in your initial email, I guessed (incorrectly) that you had not modified anything since you put in the new spark plugs and wire kit.

 To answer your question:  When pulling the Tach Drive, most of the folks I know have had a plate made that bolts on with the four corner bolts to the plate and there you go.  You make it yourself.  You need to be very very careful here, because if you remove the wrong "plate" you also will expose the gearing for the tach drive that also is part of the air distributor drive.  What I am saying here is that if you pull the wrong plates and stuff in an attempt to put a new cover plate over the tach drive, you can easily disturb the gearing inside, which will in turn through your air start distributor out of adjustment and then you are DEEP KIMSHEE!  Re-timing the airstart distributor is NOT EASY regardless of what anyone might tell you otherwise.  So Scott, be very very careful of what you take apart in that area.  Without photo's it is hard for me to describe what to take off and what not to take off.  Talk to Dennis about that for details.

 Somehow I just managed to send this message when my fingers slipped on the keyboardâ€¦ oopsâ€¦ so here is the end of the message, sorry.

 Going back to your noise on your radios.  I hate to tell you this Scott, but those new digital tachs that attach to your P leads are a real source of radio noise.  This is the forth time I have had a person who installed that tach start talking about radio noise.  I also have personal experience with that thing myself.

 Given that your Tach Generator is now removed from the aircraft, and you have installed the Digital Tach that used your P leads for a input, I am 99.999% sure that your new radio noise is from the P leads.  Yes, you should repair the shields down at the MAGâ€™s and that will help.  But you also are going to have to go back to the wires that have been attached behind the mag switch and make darn sure that shielded wires were used there as well.  Just leaving a tiny bit of exposed wire (I.E. Where there is no shielding on the P leads) will allow that to act as an antenna and RADIATE NOISE all over the aircraft.

 In one aircraft I worked on (a Sukhoi 26) I had to replace all of that wiring to the digital tach, and then... get ready for thisâ€¦.. I had to make an actual BOX out of aluminum and enclose the whole tach inside that box (a Faraday Shield per se) and ground all that.

 So that is the downside of using that kind of Tach, I am sorry to have to say.  Itâ€™s a GREAT TACH, and I love the way it works, but since it uses the P leads, you have to really pay attention to your shielding.  There is usually no filter that can eliminate this kind of noise.  Spark noise is very broad spectrum and if you are anywhere in the near field from this noise, youâ€™re pretty much screwed.

 One trick that SOMETIMES helps:  Take a handheld VHF radio, remove the antenna and stick a paperclip into the center conductor of the antenna jack.  Hook headphones to the handheld radio.  Now start the aircraft and use the radio as a â€œtest wandâ€ and run it around the wiring to try and find the source.  This is not easy and takes some effort.

 Bottom line:  Your noise is coming from your P leads and new tach.  Good luck.  Merry Christmas.

 Mark Bitterlich

 --- On Fri, 12/17/10, Scott Poehlmann<scott-p(at)texas.net>  wrote:

> From: Scott Poehlmann<scott-p(at)texas.net>

> Subject: Re: RF interference

> To: yak-list(at)matronics.com

> Date: Friday, December 17, 2010, 9:03 PM

> 

> Scott Poehlmann<scott-p(at)texas.net>

>

> Thanks Mark,

>

> I knew that you would have a great, step by step method.

>

> Went out to the hangar today: looks like the P-leads are

> the

> culprit--BOTH have the shielding detached from the

> connector and about 1

> cm of unshielded lead "hanging in the breeze". I'll spend

> some time

> tomorrow AM soldering the shielding to the connector (it

> appears that

> this has been done before and that the solder joints have

> failed...),

> and will advise if this doesn't fix the problem.

>

> Now for the next question: any ideas where to find a cover

> for the tach

> generator drive? I am running a Horizon digital tach (which

> takes its

> data from the mag--in fact it is wired into the back of the

> mag

> switch...), and I have no tach generator, just a big open

> fitting with a

> drive (and seal) at the bottom... Threaded on the outside,

> of course.

>

> Thanks again, and to everyone else who provided

> information. This list

> is a tremendous asset to the continued operation of these

> airplanes.

>

> Scott

>

> On 12-17-2010 10:15, Yak Pilot wrote:

>> 

> Pilot<yakplt(at)yahoo.com>

>> Do the following:

>>

>> Remove the plug from the Tach Gen and tie it back. Run

> the aircraft.  Does the noise go away?  Then it is

> indeed your Tach Gen and it is most likely shielding at the

> Tach Generator plug itself.  Be careful taking this

> plug apart as it is common for the soldering on these wires

> to break.

>> If the noise does not go away, fly the airplane.

> Over the airport come to complete idle and then shut the

> mags off.  Both mags, turn them off.

>> You're now a glider.

>>

>> Did the noise go away?  If it did, then you have

> a MAG noise problem.  The mag noise filters will help,

> but before you go to that effort, look at the P leak plugs

> that go into the side of the mags.  It is very common

> for people to twist these plugs off during some kind of

> maint. action and in the process twist the shield right off

> the plug as well.  If the P Lead is unshielded you will

> have one huge amount of noise.

>> If the noise is still there even when you have

> performed these steps (whcih is highly unlikely) then you've

> got some other device radiating energy in the

> aircraft.  Start turning everything that you can off to

> try and identify it.

>> Suggestions have been made to see if it is coming in

> via the antenna or the power wiring.  I have posted

> these suggestions before, but it is something you do at the

> end of troubleshooting and not the beginning.  It is

> much easier to identify the noise source and eliminate it

> where it is coming from.  If you can't identify the

> noise and you are lucky enough to have it coming in via the

> power wires (again this is rare), a choke on the input power

> wiring can help eliminate the noise.  This can be as

> simple as a snap on torroid, or an expensive (purchased)

> filter, that is usually some sort of "Pi L brute force"

> filter consisting of two caps and an inductor. 

> Usually, snap on torroids are just as effective and much

> cheaper.  Again though, noise coming in via the power

> wiring is rare.  It usually is coming in via the

> antenna, and that means you MUST eliminate the noise at it's

> source.

>> The tests described above will usually nail the

> problem in short order.

>> Mark Bitterlich

>>

>> p.s.  The reason I recommend shutting the mags

> off at idle in flight versus doing it on the ground is

> because the engine keeps wind-milling even with the mags

> off, and you can leave them off much longer while you are

> listening for radio noise and seeing if it goes away. 

> Shutting the engine off with the mags and the engine

> windmilling with it at idle will not hurt anything, although

> the engine will cool off really fast, so when you turn the

> mags back on and the engine once again is actually

> "running", don't just cob the power to 100%.  Bring it

> in slowly.  Common sense applies.

>> --- On Thu, 12/16/10, Roger Kemp M.D.<viperdoc(at)mindspring.com>

> wrote:

>>> From: Roger Kemp M.D.<viperdoc(at)mindspring.com>

>>> Subject: RE: RF interference

>>> To: yak-list(at)matronics.com

>>> Date: Thursday, December 16, 2010, 1:35 PM

>>> 

>>> "Roger Kemp M.D."<viperdoc(at)mindspring.com>

>>>

>>> Check the shielding on your Tac Generator. That is

> the most

>>> likely source

>>> for RPM related noise.

>>> Doc

>>>

>>> --

yakplt(at)yahoo.com
Guest

Posted: Sat Dec 18, 2010 4:23 pm Post subject: RF interference

Scott, 



Any wire at all that hooks to the P lead of any mag is a noise source.  Period.  How much it will influence the radio is an open question.  Many folks that are unfamiliar with radio theory think that radio interference is something you can hear in your headset.  Not necessarily the case at all.  



But the bottom line is always the bottom line.  If you as the pilot feel that your radio is performing well enough for you to be happy with it, that is all that really matters in the end.  



I am not sure why you are having such a difficult time soldering the P lead wiring, but then ... I am not there looking at it.  Normally you can remove some clamps and tie-ties (or whatever) and have plenty of slack available to be able to get that plug out into the open.  If you try to solder it without taking the time to remove all that junk so that you have some slack, you're right, it can be miserable.  



Typically, I have had to re-do the whole P lead connector, by unsoldering the center conductor from the metal piece, cutting it back and starting from scratch.  



Just be aware... anything at all attached to a P lead that is unshielded is going to radiate energy.  How much and where and if you can accept it, is of course a decision that must be made by you. 



Plate:  Get one from Jill and then you can see exactly which one that is already on there that you have to remove in order to put the new plate on. 



Take care, 



Mark





--- On Sat, 12/18/10, Scott Poehlmann <scott-p(at)texas.net> wrote:



[quote] From: Scott Poehlmann <scott-p(at)texas.net>

 Subject: Re: RF interference

 To: yak-list(at)matronics.com

 Date: Saturday, December 18, 2010, 5:32 PM

 

 Scott Poehlmann <scott-p(at)texas.net>

 

 Thanks Mark,

 

 I didn't mention the tach because, frankly, I didn't think

 about it. The 

 tach appears to be wired at the mag switch, and and that

 cabling is 

 unshielded. I don't know if that is at issue or not, but

 given what 

 happened today, I think not...

 

 Having said that, I am 98% certain I have found the

 problem. I soldered 

 the shield back on the right (#1) mag and now I have the

 problem only 

 when the left (#2) mag is operating (i.e., position "2" and

 "1+2"). I 

 will repeat the process with the left mag tomorrow, and I

 suspect that I 

 am done. I am not particularly happy with the quality of

 the solder 

 joints (it is hard to solder in the engine bay...) have you

 had any 

 experience with copper tape shielding? It seems like an

 obvious solution 

 rather than trying to solder behind the engine...

 

 I will take a photo of the location of the former tach

 generator (or at 

 least what I think is the location...) and see what you

 think. Given 

 that both Jill and George have pre-manufactured plates, I

 will likely 

 get one from one of them and put that on.

 

 Thanks again,

 

 Scott

 

 On 12-18-2010 13:33, Yak Pilot wrote:

 > -->  Yak-List message posted by: Yak

 Pilot<yakplt(at)yahoo.com>

 >

 > Hmmm!

 >

 > I need to add one step to my troubleshooting

 procedures Scott:

 >

 > Step Three:  Have you added a digital tach that

 takes it's input off the P Leads.  If so, that is very

 high potential for noise addition to your aircraft.

 >

 > I actually thought of mentioning that, but since you

 did not bring it up in your initial email, I guessed

 (incorrectly) that you had not modified anything since you

 put in the new spark plugs and wire kit.

 >

 > To answer your question:  When pulling the Tach

 Drive, most of the folks I know have had a plate made that

 bolts on with the four corner bolts to the plate and there

 you go.  You make it yourself.  You need to be

 very very careful here, because if you remove the wrong

 "plate" you also will expose the gearing for the tach drive

 that also is part of the air distributor drive.  What I

 am saying here is that if you pull the wrong plates and

 stuff in an attempt to put a new cover plate over the tach

 drive, you can easily disturb the gearing inside, which will

 in turn through your air start distributor out of adjustment

 and then you are DEEP KIMSHEE!  Re-timing the airstart

 distributor is NOT EASY regardless of what anyone might tell

 you otherwise.  So Scott, be very very careful of what

 you take apart in that area.  Without photo's it is

 hard for me to describe what to take off and what not to

 take off.  Talk to Dennis about tha

 >

 > --- On Fri, 12/17/10, Scott Poehlmann<scott-p(at)texas.net> 

 wrote:

 >

 >> From: Scott Poehlmann<scott-p(at)texas.net>

 >> Subject: Re: RF interference

 >> To: yak-list(at)matronics.com

 >> Date: Friday, December 17, 2010, 9:03 PM

 >> -->  Yak-List message posted by:

 >> Scott Poehlmann<scott-p(at)texas.net>

 >>

 >> Thanks Mark,

 >>

 >> I knew that you would have a great, step by step

 method.

 >>

 >> Went out to the hangar today: looks like the

 P-leads are

 >> the

 >> culprit--BOTH have the shielding detached from

 the

 >> connector and about 1

 >> cm of unshielded lead "hanging in the breeze".

 I'll spend

 >> some time

 >> tomorrow AM soldering the shielding to the

 connector (it

 >> appears that

 >> this has been done before and that the solder

 joints have

 >> failed...),

 >> and will advise if this doesn't fix the problem.

 >>

 >> Now for the next question: any ideas where to find

 a cover

 >> for the tach

 >> generator drive? I am running a Horizon digital

 tach (which

 >> takes its

 >> data from the mag--in fact it is wired into the

 back of the

 >> mag

 >> switch...), and I have no tach generator, just a

 big open

 >> fitting with a

 >> drive (and seal) at the bottom... Threaded on the

 outside,

 >> of course.

 >>

 >> Thanks again, and to everyone else who provided

 >> information. This list

 >> is a tremendous asset to the continued operation

 of these

 >> airplanes.

 >>

 >> Scott

 >>

 >> On 12-17-2010 10:15, Yak Pilot wrote:

 >>> -->   Yak-List message

 posted by: Yak

 >> Pilot<yakplt(at)yahoo.com>

 >>> Do the following:

 >>>

 >>> Remove the plug from the Tach Gen and tie it

 back. Run

 >> the aircraft.  Does the noise go away? 

 Then it is

 >> indeed your Tach Gen and it is most likely

 shielding at the

 >> Tach Generator plug itself.  Be careful

 taking this

 >> plug apart as it is common for the soldering on

 these wires

 >> to break.

 >>> If the noise does not go away, fly the

 airplane.

 >> Over the airport come to complete idle and then

 shut the

 >> mags off.  Both mags, turn them off.

 >>> You're now a glider.

 >>>

 >>> Did the noise go away?  If it did, then

 you have

 >> a MAG noise problem.  The mag noise filters

 will help,

 >> but before you go to that effort, look at the P

 leak plugs

 >> that go into the side of the mags.  It is

 very common

 >> for people to twist these plugs off during some

 kind of

 >> maint. action and in the process twist the shield

 right off

 >> the plug as well.  If the P Lead is

 unshielded you will

 >> have one huge amount of noise.

 >>> If the noise is still there even when you

 have

 >> performed these steps (whcih is highly unlikely)

 then you've

 >> got some other device radiating energy in the

 >> aircraft.  Start turning everything that you

 can off to

 >> try and identify it.

 >>> Suggestions have been made to see if it is

 coming in

 >> via the antenna or the power wiring.  I have

 posted

 >> these suggestions before, but it is something you

 do at the

 >> end of troubleshooting and not the

 beginning.  It is

 >> much easier to identify the noise source and

 eliminate it

 >> where it is coming from.  If you can't

 identify the

 >> noise and you are lucky enough to have it coming

 in via the

 >> power wires (again this is rare), a choke on the

 input power

 >> wiring can help eliminate the noise.  This

 can be as

 >> simple as a snap on torroid, or an expensive

 (purchased)

 >> filter, that is usually some sort of "Pi L brute

 force"

 >> filter consisting of two caps and an inductor. 

 >> Usually, snap on torroids are just as effective

 and much

 >> cheaper.  Again though, noise coming in via

 the power

 >> wiring is rare.  It usually is coming in via

 the

 >> antenna, and that means you MUST eliminate the

 noise at it's

 >> source.

 >>> The tests described above will usually nail

 the

 >> problem in short order.

 >>> Mark Bitterlich

 >>>

 >>> p.s.  The reason I recommend shutting the

 mags

 >> off at idle in flight versus doing it on the

 ground is

 >> because the engine keeps wind-milling even with

 the mags

 >> off, and you can leave them off much longer while

 you are

 >> listening for radio noise and seeing if it goes

 away. 

 >> Shutting the engine off with the mags and the

 engine

 >> windmilling with it at idle will not hurt

 anything, although

 >> the engine will cool off really fast, so when you

 turn the

 >> mags back on and the engine once again is

 actually

 >> "running", don't just cob the power to 100%. 

 Bring it

 >> in slowly.  Common sense applies.

 >>> --- On Thu, 12/16/10, Roger Kemp M.D.<viperdoc(at)mindspring.com>

 >> wrote:

 >>>> From: Roger Kemp M.D.<viperdoc(at)mindspring.com>

 >>>> Subject: RE: RF interference

 >>>> To: yak-list(at)matronics.com

 >>>> Date: Thursday, December 16, 2010, 1:35

 PM

 >>>> -->   Yak-List message

 posted by:

 >>>> "Roger Kemp M.D."<viperdoc(at)mindspring.com>

 >>>>

 >>>> Check the shielding on your Tac Generator.

 That is

 >> the most

 >>>> likely source

 >>>> for RPM related noise.

 >>>> Doc

 >>>>

 >>>> --

yakplt(at)yahoo.com
Guest

Posted: Sat Dec 18, 2010 4:34 pm Post subject: RF interference

Scott, without going into a long discussion on how radios work, the simple fact is that you can not determine how much interference you are getting simply by plugging in the headset and listening for noise.  Without using test equipment it is sometimes hard to quantify.  



However, there are some simple tests that allow the human ear to determine if you are being impacted by it or not.  



The most simple test is to tune the radio to a really weak signal that is just barely readable, and then start the engine and see how the noise impacts the reception of that signal.  That can be hard to do at the airport where most RF sources are right there on the field.  This test will only work if you can tune into a signal that is already right on the threshold of detection.  If you can do that now, great.  If not, you need a sig-gen and somebody who knows how to use it.  



Failing that, go fly and tune your radio into some ASOS or ATIS transmission a long way aways and listen to them.  Then turn off the mags and see how much the signal improves.  If it does, then you need to attack your shielding more vigorously.  If turning the engine off with the mag switch does not impact your weak received signal at all, then you have done as much as you can to shield P leads.  Crude but it will work..  



Mark Bitterlich

--- On Sat, 12/18/10, Scott Poehlmann <scott-p(at)texas.net> wrote:



[quote] From: Scott Poehlmann <scott-p(at)texas.net>

 Subject: Re: RF interference

 To: yak-list(at)matronics.com

 Date: Saturday, December 18, 2010, 5:37 PM

 

 Scott Poehlmann <scott-p(at)texas.net>

 

 Ahh.

 

 Perhaps I should shield the wires to the tach, too.Â 

 The interference 

 really does go away to essentially nothing (ok, I get an

 occasional 

 "pop" or two, but NOTHING like before) when running on just

 Mag 1 now, 

 so if I can accomplish the same thing with Mag 2, then I am

 happy.

 

 Will look into the shielding on those wires after fixing

 P-lead on Mag 

 2, and report back.

 

 Scott

 

 On 12-18-2010 13:46, Yak Pilot wrote:

 > -->Â  Yak-List message posted by: Yak

 Pilot<yakplt(at)yahoo.com>

 >

 >

 > Hmmm!

 >

 > I need to add one step to my troubleshooting

 procedures Scott:

 >

 > Step Three:Â  Have you added a digital tach that

 takes it's input off the P Leads.Â  If so, that is very

 high potential for noise addition to your aircraft.

 >

 > I actually thought of mentioning that, but since you

 did not bring it up in your initial email, I guessed

 (incorrectly) that you had not modified anything since you

 put in the new spark plugs and wire kit.

 >

 > To answer your question:Â  When pulling the Tach

 Drive, most of the folks I know have had a plate made that

 bolts on with the four corner bolts to the plate and there

 you go.Â  You make it yourself.Â  You need to be

 very very careful here, because if you remove the wrong

 "plate" you also will expose the gearing for the tach drive

 that also is part of the air distributor drive.Â  What I

 am saying here is that if you pull the wrong plates and

 stuff in an attempt to put a new cover plate over the tach

 drive, you can easily disturb the gearing inside, which will

 in turn through your air start distributor out of adjustment

 and then you are DEEP KIMSHEE!Â  Re-timing the airstart

 distributor is NOT EASY regardless of what anyone might tell

 you otherwise.Â  So Scott, be very very careful of what

 you take apart in that area.Â  Without photo's it is

 hard for me to describe what to take off and what not to

 take off.Â  Talk to Dennis about that for details.

 >

 > Somehow I just managed to send this message when my

 fingers slipped on the keyboardâ€¦ oopsâ€¦ so here is the

 end of the message, sorry.

 >

 > Going back to your noise on your radios.Â  I hate

 to tell you this Scott, but those new digital tachs that

 attach to your P leads are a real source of radio

 noise.Â  This is the forth time I have had a person who

 installed that tach start talking about radio noise.Â  I

 also have personal experience with that thing myself.

 >

 > Given that your Tach Generator is now removed from the

 aircraft, and you have installed the Digital Tach that used

 your P leads for a input, I am 99.999% sure that your new

 radio noise is from the P leads.Â  Yes, you should

 repair the shields down at the MAGâ€™s and that will

 help.Â  But you also are going to have to go back to the

 wires that have been attached behind the mag switch and make

 darn sure that shielded wires were used there as well.Â 

 Just leaving a tiny bit of exposed wire (I.E. Where there is

 no shielding on the P leads) will allow that to act as an

 antenna and RADIATE NOISE all over the aircraft.

 >

 > In one aircraft I worked on (a Sukhoi 26) I had to

 replace all of that wiring to the digital tach, and then...

 get ready for thisâ€¦.. I had to make an actual BOX out of

 aluminum and enclose the whole tach inside that box (a

 Faraday Shield per se) and ground all that.

 >

 > So that is the downside of using that kind of Tach, I

 am sorry to have to say.Â  Itâ€™s a GREAT TACH, and I

 love the way it works, but since it uses the P leads, you

 have to really pay attention to your shielding.Â  There

 is usually no filter that can eliminate this kind of

 noise.Â  Spark noise is very broad spectrum and if you

 are anywhere in the near field from this noise, youâ€™re

 pretty much screwed.

 >

 > One trick that SOMETIMES helps:Â  Take a handheld

 VHF radio, remove the antenna and stick a paperclip into the

 center conductor of the antenna jack.Â  Hook headphones

 to the handheld radio.Â  Now start the aircraft and use

 the radio as a â€œtest wandâ€ and run it around the wiring

 to try and find the source.Â  This is not easy and takes

 some effort.

 >

 > Bottom line:Â  Your noise is coming from your P

 leads and new tach.Â  Good luck.Â  Merry Christmas.

 >

 > Mark Bitterlich

 >

 >

 > --- On Fri, 12/17/10, Scott Poehlmann<scott-p(at)texas.net>Â 

 wrote:

 >

 >> From: Scott Poehlmann<scott-p(at)texas.net>

 >> Subject: Re: RF interference

 >> To: yak-list(at)matronics.com

 >> Date: Friday, December 17, 2010, 9:03 PM

 >> -->Â  Yak-List message posted by:

 >> Scott Poehlmann<scott-p(at)texas.net>

 >>

 >> Thanks Mark,

 >>

 >> I knew that you would have a great, step by step

 method.

 >>

 >> Went out to the hangar today: looks like the

 P-leads are

 >> the

 >> culprit--BOTH have the shielding detached from

 the

 >> connector and about 1

 >> cm of unshielded lead "hanging in the breeze".

 I'll spend

 >> some time

 >> tomorrow AM soldering the shielding to the

 connector (it

 >> appears that

 >> this has been done before and that the solder

 joints have

 >> failed...),

 >> and will advise if this doesn't fix the problem.

 >>

 >> Now for the next question: any ideas where to find

 a cover

 >> for the tach

 >> generator drive? I am running a Horizon digital

 tach (which

 >> takes its

 >> data from the mag--in fact it is wired into the

 back of the

 >> mag

 >> switch...), and I have no tach generator, just a

 big open

 >> fitting with a

 >> drive (and seal) at the bottom... Threaded on the

 outside,

 >> of course.

 >>

 >> Thanks again, and to everyone else who provided

 >> information. This list

 >> is a tremendous asset to the continued operation

 of these

 >> airplanes.

 >>

 >> Scott

 >>

 >> On 12-17-2010 10:15, Yak Pilot wrote:

 >>> -->Â Â Â Yak-List message

 posted by: Yak

 >> Pilot<yakplt(at)yahoo.com>

 >>> Do the following:

 >>>

 >>> Remove the plug from the Tach Gen and tie it

 back. Run

 >> the aircraft.Â  Does the noise go away?Â 

 Then it is

 >> indeed your Tach Gen and it is most likely

 shielding at the

 >> Tach Generator plug itself.Â  Be careful

 taking this

 >> plug apart as it is common for the soldering on

 these wires

 >> to break.

 >>> If the noise does not go away, fly the

 airplane.

 >> Over the airport come to complete idle and then

 shut the

 >> mags off.Â  Both mags, turn them off.

 >>> You're now a glider.

 >>>

 >>> Did the noise go away?Â  If it did, then

 you have

 >> a MAG noise problem.Â  The mag noise filters

 will help,

 >> but before you go to that effort, look at the P

 leak plugs

 >> that go into the side of the mags.Â  It is

 very common

 >> for people to twist these plugs off during some

 kind of

 >> maint. action and in the process twist the shield

 right off

 >> the plug as well.Â  If the P Lead is

 unshielded you will

 >> have one huge amount of noise.

 >>> If the noise is still there even when you

 have

 >> performed these steps (whcih is highly unlikely)

 then you've

 >> got some other device radiating energy in the

 >> aircraft.Â  Start turning everything that you

 can off to

 >> try and identify it.

 >>> Suggestions have been made to see if it is

 coming in

 >> via the antenna or the power wiring.Â  I have

 posted

 >> these suggestions before, but it is something you

 do at the

 >> end of troubleshooting and not the

 beginning.Â  It is

 >> much easier to identify the noise source and

 eliminate it

 >> where it is coming from.Â  If you can't

 identify the

 >> noise and you are lucky enough to have it coming

 in via the

 >> power wires (again this is rare), a choke on the

 input power

 >> wiring can help eliminate the noise.Â  This

 can be as

 >> simple as a snap on torroid, or an expensive

 (purchased)

 >> filter, that is usually some sort of "Pi L brute

 force"

 >> filter consisting of two caps and an inductor. 

 >> Usually, snap on torroids are just as effective

 and much

 >> cheaper.Â  Again though, noise coming in via

 the power

 >> wiring is rare.Â  It usually is coming in via

 the

 >> antenna, and that means you MUST eliminate the

 noise at it's

 >> source.

 >>> The tests described above will usually nail

 the

 >> problem in short order.

 >>> Mark Bitterlich

 >>>

 >>> p.s.Â  The reason I recommend shutting the

 mags

 >> off at idle in flight versus doing it on the

 ground is

 >> because the engine keeps wind-milling even with

 the mags

 >> off, and you can leave them off much longer while

 you are

 >> listening for radio noise and seeing if it goes

 away. 

 >> Shutting the engine off with the mags and the

 engine

 >> windmilling with it at idle will not hurt

 anything, although

 >> the engine will cool off really fast, so when you

 turn the

 >> mags back on and the engine once again is

 actually

 >> "running", don't just cob the power to 100%.Â 

 Bring it

 >> in slowly.Â  Common sense applies.

 >>> --- On Thu, 12/16/10, Roger Kemp M.D.<viperdoc(at)mindspring.com>

 >> wrote:

 >>>> From: Roger Kemp M.D.<viperdoc(at)mindspring.com>

 >>>> Subject: RE: RF interference

 >>>> To: yak-list(at)matronics.com

 >>>> Date: Thursday, December 16, 2010, 1:35

 PM

 >>>> -->Â Â Â Yak-List message

 posted by:

 >>>> "Roger Kemp M.D."<viperdoc(at)mindspring.com>

 >>>>

 >>>> Check the shielding on your Tac Generator.

 That is

 >> the most

 >>>> likely source

 >>>> for RPM related noise.

 >>>> Doc

 >>>>

 >>>> --

scott-p(at)texas.net
Guest

Posted: Sat Dec 18, 2010 7:45 pm Post subject: RF interference

Hi Mark,



Of course this all makes sense, and you are right. Fortunately I have 

such a source readily available... the ATIS on the field at ELP is 11 NM 

away--straight LOS through a mountain. Under good circumstances it is 

just audible on my field (when the Mexican cell phones are playing 

tricks, it isn't audible at all, but that's another story...), so I can 

use that for the test you propose. I don't have access to a signal 

generator, nor do I have any interest in trying to mess with it beyond 

that which is required to obtain good communication in both directions.



I am just happy it is something straightforward and not in the power 

system. I was not looking forward to that job. Frankly, shielding the 

wires from the mag switch to the tach should be easy (it's all behind 

the panel with a total run of less than 2 feet). Now the question which 

end to ground, and to what? Do you know if the housing of the mag switch 

will tolerate being grounded (perhaps it already IS grounded?) or does 

it need to "float"?



Thanks,



Scott



On 12-18-2010 17:31, Yak Pilot wrote:

[quote] 



 Scott, without going into a long discussion on how radios work, the simple fact is that you can not determine how much interference you are getting simply by plugging in the headset and listening for noise.  Without using test equipment it is sometimes hard to quantify.



 However, there are some simple tests that allow the human ear to determine if you are being impacted by it or not.



 The most simple test is to tune the radio to a really weak signal that is just barely readable, and then start the engine and see how the noise impacts the reception of that signal.  That can be hard to do at the airport where most RF sources are right there on the field.  This test will only work if you can tune into a signal that is already right on the threshold of detection.  If you can do that now, great.  If not, you need a sig-gen and somebody who knows how to use it.



 Failing that, go fly and tune your radio into some ASOS or ATIS transmission a long way aways and listen to them.  Then turn off the mags and see how much the signal improves.  If it does, then you need to attack your shielding more vigorously.  If turning the engine off with the mag switch does not impact your weak received signal at all, then you have done as much as you can to shield P leads.  Crude but it will work..



 Mark Bitterlich

 --- On Sat, 12/18/10, Scott Poehlmann<scott-p(at)texas.net>  wrote:



> From: Scott Poehlmann<scott-p(at)texas.net>

> Subject: Re: RF interference

> To: yak-list(at)matronics.com

> Date: Saturday, December 18, 2010, 5:37 PM

> 

> Scott Poehlmann<scott-p(at)texas.net>

>

> Ahh.

>

> Perhaps I should shield the wires to the tach, too. 

> The interference

> really does go away to essentially nothing (ok, I get an

> occasional

> "pop" or two, but NOTHING like before) when running on just

> Mag 1 now,

> so if I can accomplish the same thing with Mag 2, then I am

> happy.

>

> Will look into the shielding on those wires after fixing

> P-lead on Mag

> 2, and report back.

>

> Scott

>

> On 12-18-2010 13:46, Yak Pilot wrote:

>> 

> Pilot<yakplt(at)yahoo.com>

>>

>> Hmmm!

>>

>> I need to add one step to my troubleshooting

> procedures Scott:

>> Step Three:  Have you added a digital tach that

> takes it's input off the P Leads.  If so, that is very

> high potential for noise addition to your aircraft.

>> I actually thought of mentioning that, but since you

> did not bring it up in your initial email, I guessed

> (incorrectly) that you had not modified anything since you

> put in the new spark plugs and wire kit.

>> To answer your question:  When pulling the Tach

> Drive, most of the folks I know have had a plate made that

> bolts on with the four corner bolts to the plate and there

> you go.  You make it yourself.  You need to be

> very very careful here, because if you remove the wrong

> "plate" you also will expose the gearing for the tach drive

> that also is part of the air distributor drive.  What I

> am saying here is that if you pull the wrong plates and

> stuff in an attempt to put a new cover plate over the tach

> drive, you can easily disturb the gearing inside, which will

> in turn through your air start distributor out of adjustment

> and then you are DEEP KIMSHEE!  Re-timing the airstart

> distributor is NOT EASY regardless of what anyone might tell

> you otherwise.  So Scott, be very very careful of what

> you take apart in that area.  Without photo's it is

> hard for me to describe what to take off and what not to

> take off.  Talk to Dennis about that for details.

>> Somehow I just managed to send this message when my

> fingers slipped on the keyboardâ€¦ oopsâ€¦ so here is the

> end of the message, sorry.

>> Going back to your noise on your radios.  I hate

> to tell you this Scott, but those new digital tachs that

> attach to your P leads are a real source of radio

> noise.  This is the forth time I have had a person who

> installed that tach start talking about radio noise.  I

> also have personal experience with that thing myself.

>> Given that your Tach Generator is now removed from the

> aircraft, and you have installed the Digital Tach that used

> your P leads for a input, I am 99.999% sure that your new

> radio noise is from the P leads.  Yes, you should

> repair the shields down at the MAGâ€™s and that will

> help.  But you also are going to have to go back to the

> wires that have been attached behind the mag switch and make

> darn sure that shielded wires were used there as well. 

> Just leaving a tiny bit of exposed wire (I.E. Where there is

> no shielding on the P leads) will allow that to act as an

> antenna and RADIATE NOISE all over the aircraft.

>> In one aircraft I worked on (a Sukhoi 26) I had to

> replace all of that wiring to the digital tach, and then...

> get ready for thisâ€¦.. I had to make an actual BOX out of

> aluminum and enclose the whole tach inside that box (a

> Faraday Shield per se) and ground all that.

>> So that is the downside of using that kind of Tach, I

> am sorry to have to say.  Itâ€™s a GREAT TACH, and I

> love the way it works, but since it uses the P leads, you

> have to really pay attention to your shielding.  There

> is usually no filter that can eliminate this kind of

> noise.  Spark noise is very broad spectrum and if you

> are anywhere in the near field from this noise, youâ€™re

> pretty much screwed.

>> One trick that SOMETIMES helps:  Take a handheld

> VHF radio, remove the antenna and stick a paperclip into the

> center conductor of the antenna jack.  Hook headphones

> to the handheld radio.  Now start the aircraft and use

> the radio as a â€œtest wandâ€ and run it around the wiring

> to try and find the source.  This is not easy and takes

> some effort.

>> Bottom line:  Your noise is coming from your P

> leads and new tach.  Good luck.  Merry Christmas.

>> Mark Bitterlich

>>

>>

>> --- On Fri, 12/17/10, Scott Poehlmann<scott-p(at)texas.net>

> wrote:

>>> From: Scott Poehlmann<scott-p(at)texas.net>

>>> Subject: Re: RF interference

>>> To: yak-list(at)matronics.com

>>> Date: Friday, December 17, 2010, 9:03 PM

>>> 

>>> Scott Poehlmann<scott-p(at)texas.net>

>>>

>>> Thanks Mark,

>>>

>>> I knew that you would have a great, step by step

> method.

>>> Went out to the hangar today: looks like the

> P-leads are

>>> the

>>> culprit--BOTH have the shielding detached from

> the

>>> connector and about 1

>>> cm of unshielded lead "hanging in the breeze".

> I'll spend

>>> some time

>>> tomorrow AM soldering the shielding to the

> connector (it

>>> appears that

>>> this has been done before and that the solder

> joints have

>>> failed...),

>>> and will advise if this doesn't fix the problem.

>>>

>>> Now for the next question: any ideas where to find

> a cover

>>> for the tach

>>> generator drive? I am running a Horizon digital

> tach (which

>>> takes its

>>> data from the mag--in fact it is wired into the

> back of the

>>> mag

>>> switch...), and I have no tach generator, just a

> big open

>>> fitting with a

>>> drive (and seal) at the bottom... Threaded on the

> outside,

>>> of course.

>>>

>>> Thanks again, and to everyone else who provided

>>> information. This list

>>> is a tremendous asset to the continued operation

> of these

>>> airplanes.

>>>

>>> Scott

>>>

>>> On 12-17-2010 10:15, Yak Pilot wrote:

>>>> -->    Yak-List message

> posted by: Yak

>>> Pilot<yakplt(at)yahoo.com>

>>>> Do the following:

>>>>

>>>> Remove the plug from the Tach Gen and tie it

> back. Run

>>> the aircraft.  Does the noise go away?

> Then it is

>>> indeed your Tach Gen and it is most likely

> shielding at the

>>> Tach Generator plug itself.  Be careful

> taking this

>>> plug apart as it is common for the soldering on

> these wires

>>> to break.

>>>> If the noise does not go away, fly the

> airplane.

>>> Over the airport come to complete idle and then

> shut the

>>> mags off.  Both mags, turn them off.

>>>> You're now a glider.

>>>>

>>>> Did the noise go away?  If it did, then

> you have

>>> a MAG noise problem.  The mag noise filters

> will help,

>>> but before you go to that effort, look at the P

> leak plugs

>>> that go into the side of the mags.  It is

> very common

>>> for people to twist these plugs off during some

> kind of

>>> maint. action and in the process twist the shield

> right off

>>> the plug as well.  If the P Lead is

> unshielded you will

>>> have one huge amount of noise.

>>>> If the noise is still there even when you

> have

>>> performed these steps (whcih is highly unlikely)

> then you've

>>> got some other device radiating energy in the

>>> aircraft.  Start turning everything that you

> can off to

>>> try and identify it.

>>>> Suggestions have been made to see if it is

> coming in

>>> via the antenna or the power wiring.  I have

> posted

>>> these suggestions before, but it is something you

> do at the

>>> end of troubleshooting and not the

> beginning.  It is

>>> much easier to identify the noise source and

> eliminate it

>>> where it is coming from.  If you can't

> identify the

>>> noise and you are lucky enough to have it coming

> in via the

>>> power wires (again this is rare), a choke on the

> input power

>>> wiring can help eliminate the noise.  This

> can be as

>>> simple as a snap on torroid, or an expensive

> (purchased)

>>> filter, that is usually some sort of "Pi L brute

> force"

>>> filter consisting of two caps and an inductor.

>>> Usually, snap on torroids are just as effective

> and much

>>> cheaper.  Again though, noise coming in via

> the power

>>> wiring is rare.  It usually is coming in via

> the

>>> antenna, and that means you MUST eliminate the

> noise at it's

>>> source.

>>>> The tests described above will usually nail

> the

>>> problem in short order.

>>>> Mark Bitterlich

>>>>

>>>> p.s.  The reason I recommend shutting the

> mags

>>> off at idle in flight versus doing it on the

> ground is

>>> because the engine keeps wind-milling even with

> the mags

>>> off, and you can leave them off much longer while

> you are

>>> listening for radio noise and seeing if it goes

> away.

>>> Shutting the engine off with the mags and the

> engine

>>> windmilling with it at idle will not hurt

> anything, although

>>> the engine will cool off really fast, so when you

> turn the

>>> mags back on and the engine once again is

> actually

>>> "running", don't just cob the power to 100%.

> Bring it

>>> in slowly.  Common sense applies.

>>>> --- On Thu, 12/16/10, Roger Kemp M.D.<viperdoc(at)mindspring.com>

>>> wrote:

>>>>> From: Roger Kemp M.D.<viperdoc(at)mindspring.com>

>>>>> Subject: RE: RF interference

>>>>> To: yak-list(at)matronics.com

>>>>> Date: Thursday, December 16, 2010, 1:35

> PM

>>>>> -->    Yak-List message

> posted by:

>>>>> "Roger Kemp M.D."<viperdoc(at)mindspring.com>

>>>>>

>>>>> Check the shielding on your Tac Generator.

> That is

>>> the most

>>>>> likely source

>>>>> for RPM related noise.

>>>>> Doc

>>>>>

>>>>> --

dsavarese0812(at)bellsout
Guest

Posted: Sun Dec 19, 2010 8:03 am Post subject: RF interference

Scott,

The back of the mag switch is in a metal "can".  At the rear of the 

"can" the braided shield of the P leads is affixed to the "can", thus 

grounding it.  FWIW, assuming the mag switch is wired correctly and 

looking at the front of the mag switch, the #1 position is the left mag, 

looking at the engine from the cockpit.  When the mag switch is in the 

#1 position, #2 mag P lead is grounded and vice versa when the switch is 

in the #2 position.

Dennis



On 12/18/2010 9:43 PM, Scott Poehlmann wrote:

[quote] 



 Hi Mark,



 Of course this all makes sense, and you are right. Fortunately I have 

 such a source readily available... the ATIS on the field at ELP is 11 

 NM away--straight LOS through a mountain. Under good circumstances it 

 is just audible on my field (when the Mexican cell phones are playing 

 tricks, it isn't audible at all, but that's another story...), so I 

 can use that for the test you propose. I don't have access to a signal 

 generator, nor do I have any interest in trying to mess with it beyond 

 that which is required to obtain good communication in both directions.



 I am just happy it is something straightforward and not in the power 

 system. I was not looking forward to that job. Frankly, shielding the 

 wires from the mag switch to the tach should be easy (it's all behind 

 the panel with a total run of less than 2 feet). Now the question 

 which end to ground, and to what? Do you know if the housing of the 

 mag switch will tolerate being grounded (perhaps it already IS 

 grounded?) or does it need to "float"?



 Thanks,



 Scott



 On 12-18-2010 17:31, Yak Pilot wrote:

> 

>

> Scott, without going into a long discussion on how radios work, the 

> simple fact is that you can not determine how much interference you 

> are getting simply by plugging in the headset and listening for 

> noise.  Without using test equipment it is sometimes hard to quantify.

>

> However, there are some simple tests that allow the human ear to 

> determine if you are being impacted by it or not.

>

> The most simple test is to tune the radio to a really weak signal 

> that is just barely readable, and then start the engine and see how 

> the noise impacts the reception of that signal.  That can be hard to 

> do at the airport where most RF sources are right there on the 

> field.  This test will only work if you can tune into a signal that 

> is already right on the threshold of detection.  If you can do that 

> now, great.  If not, you need a sig-gen and somebody who knows how to 

> use it.

>

> Failing that, go fly and tune your radio into some ASOS or ATIS 

> transmission a long way aways and listen to them.  Then turn off the 

> mags and see how much the signal improves.  If it does, then you need 

> to attack your shielding more vigorously.  If turning the engine off 

> with the mag switch does not impact your weak received signal at all, 

> then you have done as much as you can to shield P leads.  Crude but 

> it will work..

>

> Mark Bitterlich

> --- On Sat, 12/18/10, Scott Poehlmann<scott-p(at)texas.net>  wrote:

>

>> From: Scott Poehlmann<scott-p(at)texas.net>

>> Subject: Re: RF interference

>> To: yak-list(at)matronics.com

>> Date: Saturday, December 18, 2010, 5:37 PM

>> 

>> Scott Poehlmann<scott-p(at)texas.net>

>>

>> Ahh.

>>

>> Perhaps I should shield the wires to the tach, too. The interference

>> really does go away to essentially nothing (ok, I get an

>> occasional

>> "pop" or two, but NOTHING like before) when running on just

>> Mag 1 now,

>> so if I can accomplish the same thing with Mag 2, then I am

>> happy.

>>

>> Will look into the shielding on those wires after fixing

>> P-lead on Mag

>> 2, and report back.

>>

>> Scott

>>

>> On 12-18-2010 13:46, Yak Pilot wrote:

>>> 

>> Pilot<yakplt(at)yahoo.com>

>>>

>>> Hmmm!

>>>

>>> I need to add one step to my troubleshooting

>> procedures Scott:

>>> Step Three:  Have you added a digital tach that

>> takes it's input off the P Leads.  If so, that is very

>> high potential for noise addition to your aircraft.

>>> I actually thought of mentioning that, but since you

>> did not bring it up in your initial email, I guessed

>> (incorrectly) that you had not modified anything since you

>> put in the new spark plugs and wire kit.

>>> To answer your question:  When pulling the Tach

>> Drive, most of the folks I know have had a plate made that

>> bolts on with the four corner bolts to the plate and there

>> you go.  You make it yourself.  You need to be

>> very very careful here, because if you remove the wrong

>> "plate" you also will expose the gearing for the tach drive

>> that also is part of the air distributor drive.  What I

>> am saying here is that if you pull the wrong plates and

>> stuff in an attempt to put a new cover plate over the tach

>> drive, you can easily disturb the gearing inside, which will

>> in turn through your air start distributor out of adjustment

>> and then you are DEEP KIMSHEE!  Re-timing the airstart

>> distributor is NOT EASY regardless of what anyone might tell

>> you otherwise.  So Scott, be very very careful of what

>> you take apart in that area.  Without photo's it is

>> hard for me to describe what to take off and what not to

>> take off.  Talk to Dennis about that for details.

>>> Somehow I just managed to send this message when my

>> fingers slipped on the keyboardâ€¦ oopsâ€¦ so here is the

>> end of the message, sorry.

>>> Going back to your noise on your radios.  I hate

>> to tell you this Scott, but those new digital tachs that

>> attach to your P leads are a real source of radio

>> noise.  This is the forth time I have had a person who

>> installed that tach start talking about radio noise.  I

>> also have personal experience with that thing myself.

>>> Given that your Tach Generator is now removed from the

>> aircraft, and you have installed the Digital Tach that used

>> your P leads for a input, I am 99.999% sure that your new

>> radio noise is from the P leads.  Yes, you should

>> repair the shields down at the MAGâ€™s and that will

>> help.  But you also are going to have to go back to the

>> wires that have been attached behind the mag switch and make

>> darn sure that shielded wires were used there as well. Just leaving 

>> a tiny bit of exposed wire (I.E. Where there is

>> no shielding on the P leads) will allow that to act as an

>> antenna and RADIATE NOISE all over the aircraft.

>>> In one aircraft I worked on (a Sukhoi 26) I had to

>> replace all of that wiring to the digital tach, and then...

>> get ready for thisâ€¦.. I had to make an actual BOX out of

>> aluminum and enclose the whole tach inside that box (a

>> Faraday Shield per se) and ground all that.

>>> So that is the downside of using that kind of Tach, I

>> am sorry to have to say.  Itâ€™s a GREAT TACH, and I

>> love the way it works, but since it uses the P leads, you

>> have to really pay attention to your shielding.  There

>> is usually no filter that can eliminate this kind of

>> noise.  Spark noise is very broad spectrum and if you

>> are anywhere in the near field from this noise, youâ€™re

>> pretty much screwed.

>>> One trick that SOMETIMES helps:  Take a handheld

>> VHF radio, remove the antenna and stick a paperclip into the

>> center conductor of the antenna jack.  Hook headphones

>> to the handheld radio.  Now start the aircraft and use

>> the radio as a â€œtest wandâ€ and run it around the wiring

>> to try and find the source.  This is not easy and takes

>> some effort.

>>> Bottom line:  Your noise is coming from your P

>> leads and new tach.  Good luck.  Merry Christmas.

>>> Mark Bitterlich

>>>

>>>

>>> --- On Fri, 12/17/10, Scott Poehlmann<scott-p(at)texas.net>

>> wrote:

>>>> From: Scott Poehlmann<scott-p(at)texas.net>

>>>> Subject: Re: RF interference

>>>> To: yak-list(at)matronics.com

>>>> Date: Friday, December 17, 2010, 9:03 PM

>>>> 

>>>> Scott Poehlmann<scott-p(at)texas.net>

>>>>

>>>> Thanks Mark,

>>>>

>>>> I knew that you would have a great, step by step

>> method.

>>>> Went out to the hangar today: looks like the

>> P-leads are

>>>> the

>>>> culprit--BOTH have the shielding detached from

>> the

>>>> connector and about 1

>>>> cm of unshielded lead "hanging in the breeze".

>> I'll spend

>>>> some time

>>>> tomorrow AM soldering the shielding to the

>> connector (it

>>>> appears that

>>>> this has been done before and that the solder

>> joints have

>>>> failed...),

>>>> and will advise if this doesn't fix the problem.

>>>>

>>>> Now for the next question: any ideas where to find

>> a cover

>>>> for the tach

>>>> generator drive? I am running a Horizon digital

>> tach (which

>>>> takes its

>>>> data from the mag--in fact it is wired into the

>> back of the

>>>> mag

>>>> switch...), and I have no tach generator, just a

>> big open

>>>> fitting with a

>>>> drive (and seal) at the bottom... Threaded on the

>> outside,

>>>> of course.

>>>>

>>>> Thanks again, and to everyone else who provided

>>>> information. This list

>>>> is a tremendous asset to the continued operation

>> of these

>>>> airplanes.

>>>>

>>>> Scott

>>>>

>>>> On 12-17-2010 10:15, Yak Pilot wrote:

>>>>> -->    Yak-List message

>> posted by: Yak

>>>> Pilot<yakplt(at)yahoo.com>

>>>>> Do the following:

>>>>>

>>>>> Remove the plug from the Tach Gen and tie it

>> back. Run

>>>> the aircraft.  Does the noise go away?

>> Then it is

>>>> indeed your Tach Gen and it is most likely

>> shielding at the

>>>> Tach Generator plug itself.  Be careful

>> taking this

>>>> plug apart as it is common for the soldering on

>> these wires

>>>> to break.

>>>>> If the noise does not go away, fly the

>> airplane.

>>>> Over the airport come to complete idle and then

>> shut the

>>>> mags off.  Both mags, turn them off.

>>>>> You're now a glider.

>>>>>

>>>>> Did the noise go away?  If it did, then

>> you have

>>>> a MAG noise problem.  The mag noise filters

>> will help,

>>>> but before you go to that effort, look at the P

>> leak plugs

>>>> that go into the side of the mags.  It is

>> very common

>>>> for people to twist these plugs off during some

>> kind of

>>>> maint. action and in the process twist the shield

>> right off

>>>> the plug as well.  If the P Lead is

>> unshielded you will

>>>> have one huge amount of noise.

>>>>> If the noise is still there even when you

>> have

>>>> performed these steps (whcih is highly unlikely)

>> then you've

>>>> got some other device radiating energy in the

>>>> aircraft.  Start turning everything that you

>> can off to

>>>> try and identify it.

>>>>> Suggestions have been made to see if it is

>> coming in

>>>> via the antenna or the power wiring.  I have

>> posted

>>>> these suggestions before, but it is something you

>> do at the

>>>> end of troubleshooting and not the

>> beginning.  It is

>>>> much easier to identify the noise source and

>> eliminate it

>>>> where it is coming from.  If you can't

>> identify the

>>>> noise and you are lucky enough to have it coming

>> in via the

>>>> power wires (again this is rare), a choke on the

>> input power

>>>> wiring can help eliminate the noise.  This

>> can be as

>>>> simple as a snap on torroid, or an expensive

>> (purchased)

>>>> filter, that is usually some sort of "Pi L brute

>> force"

>>>> filter consisting of two caps and an inductor.

>>>> Usually, snap on torroids are just as effective

>> and much

>>>> cheaper.  Again though, noise coming in via

>> the power

>>>> wiring is rare.  It usually is coming in via

>> the

>>>> antenna, and that means you MUST eliminate the

>> noise at it's

>>>> source.

>>>>> The tests described above will usually nail

>> the

>>>> problem in short order.

>>>>> Mark Bitterlich

>>>>>

>>>>> p.s.  The reason I recommend shutting the

>> mags

>>>> off at idle in flight versus doing it on the

>> ground is

>>>> because the engine keeps wind-milling even with

>> the mags

>>>> off, and you can leave them off much longer while

>> you are

>>>> listening for radio noise and seeing if it goes

>> away.

>>>> Shutting the engine off with the mags and the

>> engine

>>>> windmilling with it at idle will not hurt

>> anything, although

>>>> the engine will cool off really fast, so when you

>> turn the

>>>> mags back on and the engine once again is

>> actually

>>>> "running", don't just cob the power to 100%.

>> Bring it

>>>> in slowly.  Common sense applies.

>>>>> --- On Thu, 12/16/10, Roger Kemp M.D.<viperdoc(at)mindspring.com>

>>>> wrote:

>>>>>> From: Roger Kemp M.D.<viperdoc(at)mindspring.com>

>>>>>> Subject: RE: RF interference

>>>>>> To: yak-list(at)matronics.com

>>>>>> Date: Thursday, December 16, 2010, 1:35

>> PM

>>>>>> -->    Yak-List message

>> posted by:

>>>>>> "Roger Kemp M.D."<viperdoc(at)mindspring.com>

>>>>>>

>>>>>> Check the shielding on your Tac Generator.

>> That is

>>>> the most

>>>>>> likely source

>>>>>> for RPM related noise.

>>>>>> Doc

>>>>>>

>>>>>> --

yakplt(at)yahoo.com
Guest

Posted: Sun Dec 19, 2010 1:35 pm Post subject: RF interference

Good question.  



Normally it is OK to ground both ends of the shield unless you are worried about "shield conduction".  This is a case where the shield that is grounded at both ends in an aircraft becomes a better conductor of electricity than the frame of the aircraft itself.  Some folks refer to this as a "ground loop".  



If you are worried about it, just ground one end.  But honestly, I doubt if you would have a problem grounding BOTH ends.  



I really am not sure about the mag switch itself, but it should be already grounded.  Just using shielded wire on the P leads and grounding the shield at each end should go miles and miles towards reducing noise. 



Mark Bitterlich

--- On Sat, 12/18/10, Scott Poehlmann <scott-p(at)texas.net> wrote:



[quote] From: Scott Poehlmann <scott-p(at)texas.net>

 Subject: Re: RF interference

 To: yak-list(at)matronics.com

 Date: Saturday, December 18, 2010, 10:43 PM

 

 Scott Poehlmann <scott-p(at)texas.net>

 

 Hi Mark,

 

 Of course this all makes sense, and you are right.

 Fortunately I have 

 such a source readily available... the ATIS on the field at

 ELP is 11 NM 

 away--straight LOS through a mountain. Under good

 circumstances it is 

 just audible on my field (when the Mexican cell phones are

 playing 

 tricks, it isn't audible at all, but that's another

 story...), so I can 

 use that for the test you propose. I don't have access to a

 signal 

 generator, nor do I have any interest in trying to mess

 with it beyond 

 that which is required to obtain good communication in both

 directions.

 

 I am just happy it is something straightforward and not in

 the power 

 system. I was not looking forward to that job. Frankly,

 shielding the 

 wires from the mag switch to the tach should be easy (it's

 all behind 

 the panel with a total run of less than 2 feet). Now the

 question which 

 end to ground, and to what? Do you know if the housing of

 the mag switch 

 will tolerate being grounded (perhaps it already IS

 grounded?) or does 

 it need to "float"?

 

 Thanks,

 

 Scott

 

 

 

 On 12-18-2010 17:31, Yak Pilot wrote:

 > -->Â  Yak-List message posted by: Yak

 Pilot<yakplt(at)yahoo.com>

 >

 > Scott, without going into a long discussion on how

 radios work, the simple fact is that you can not determine

 how much interference you are getting simply by plugging in

 the headset and listening for noise.Â  Without using

 test equipment it is sometimes hard to quantify.

 >

 > However, there are some simple tests that allow the

 human ear to determine if you are being impacted by it or

 not.

 >

 > The most simple test is to tune the radio to a really

 weak signal that is just barely readable, and then start the

 engine and see how the noise impacts the reception of that

 signal.Â  That can be hard to do at the airport where

 most RF sources are right there on the field.Â  This

 test will only work if you can tune into a signal that is

 already right on the threshold of detection.Â  If you

 can do that now, great.Â  If not, you need a sig-gen and

 somebody who knows how to use it.

 >

 > Failing that, go fly and tune your radio into some

 ASOS or ATIS transmission a long way aways and listen to

 them.Â  Then turn off the mags and see how much the

 signal improves.Â  If it does, then you need to attack

 your shielding more vigorously.Â  If turning the engine

 off with the mag switch does not impact your weak received

 signal at all, then you have done as much as you can to

 shield P leads.Â  Crude but it will work..

 >

 > Mark Bitterlich

 >

 >

 > --- On Sat, 12/18/10, Scott Poehlmann<scott-p(at)texas.net>Â 

 wrote:

 >

 >> From: Scott Poehlmann<scott-p(at)texas.net>

 >> Subject: Re: RF interference

 >> To: yak-list(at)matronics.com

 >> Date: Saturday, December 18, 2010, 5:37 PM

 >> -->Â  Yak-List message posted by:

 >> Scott Poehlmann<scott-p(at)texas.net>

 >>

 >> Ahh.

 >>

 >> Perhaps I should shield the wires to the tach,

 too. 

 >> The interference

 >> really does go away to essentially nothing (ok, I

 get an

 >> occasional

 >> "pop" or two, but NOTHING like before) when

 running on just

 >> Mag 1 now,

 >> so if I can accomplish the same thing with Mag 2,

 then I am

 >> happy.

 >>

 >> Will look into the shielding on those wires after

 fixing

 >> P-lead on Mag

 >> 2, and report back.

 >>

 >> Scott

 >>

 >> On 12-18-2010 13:46, Yak Pilot wrote:

 >>> -->Â Â Â Yak-List message

 posted by: Yak

 >> Pilot<yakplt(at)yahoo.com>

 >>>

 >>> Hmmm!

 >>>

 >>> I need to add one step to my troubleshooting

 >> procedures Scott:

 >>> Step Three:Â  Have you added a digital

 tach that

 >> takes it's input off the P Leads.Â  If so,

 that is very

 >> high potential for noise addition to your

 aircraft.

 >>> I actually thought of mentioning that, but

 since you

 >> did not bring it up in your initial email, I

 guessed

 >> (incorrectly) that you had not modified anything

 since you

 >> put in the new spark plugs and wire kit.

 >>> To answer your question:Â  When pulling

 the Tach

 >> Drive, most of the folks I know have had a plate

 made that

 >> bolts on with the four corner bolts to the plate

 and there

 >> you go.Â  You make it yourself.Â  You need

 to be

 >> very very careful here, because if you remove the

 wrong

 >> "plate" you also will expose the gearing for the

 tach drive

 >> that also is part of the air distributor

 drive.Â  What I

 >> am saying here is that if you pull the wrong

 plates and

 >> stuff in an attempt to put a new cover plate over

 the tach

 >> drive, you can easily disturb the gearing inside,

 which will

 >> in turn through your air start distributor out of

 adjustment

 >> and then you are DEEP KIMSHEE!Â  Re-timing the

 airstart

 >> distributor is NOT EASY regardless of what anyone

 might tell

 >> you otherwise.Â  So Scott, be very very

 careful of what

 >> you take apart in that area.Â  Without photo's

 it is

 >> hard for me to describe what to take off and what

 not to

 >> take off.Â  Talk to Dennis about that for

 details.

 >>> Somehow I just managed to send this message

 when my

 >> fingers slipped on the keyboardâ€¦ oopsâ€¦ so here

 is the

 >> end of the message, sorry.

 >>> Going back to your noise on your radios.Â 

 I hate

 >> to tell you this Scott, but those new digital

 tachs that

 >> attach to your P leads are a real source of radio

 >> noise.Â  This is the forth time I have had a

 person who

 >> installed that tach start talking about radio

 noise.Â  I

 >> also have personal experience with that thing

 myself.

 >>> Given that your Tach Generator is now removed

 from the

 >> aircraft, and you have installed the Digital Tach

 that used

 >> your P leads for a input, I am 99.999% sure that

 your new

 >> radio noise is from the P leads.Â  Yes, you

 should

 >> repair the shields down at the MAGâ€™s and that

 will

 >> help.Â  But you also are going to have to go

 back to the

 >> wires that have been attached behind the mag

 switch and make

 >> darn sure that shielded wires were used there as

 well. 

 >> Just leaving a tiny bit of exposed wire (I.E.

 Where there is

 >> no shielding on the P leads) will allow that to

 act as an

 >> antenna and RADIATE NOISE all over the aircraft.

 >>> In one aircraft I worked on (a Sukhoi 26) I

 had to

 >> replace all of that wiring to the digital tach,

 and then...

 >> get ready for thisâ€¦.. I had to make an actual

 BOX out of

 >> aluminum and enclose the whole tach inside that

 box (a

 >> Faraday Shield per se) and ground all that.

 >>> So that is the downside of using that kind of

 Tach, I

 >> am sorry to have to say.Â  Itâ€™s a GREAT

 TACH, and I

 >> love the way it works, but since it uses the P

 leads, you

 >> have to really pay attention to your

 shielding.Â  There

 >> is usually no filter that can eliminate this kind

 of

 >> noise.Â  Spark noise is very broad spectrum

 and if you

 >> are anywhere in the near field from this noise,

 youâ€™re

 >> pretty much screwed.

 >>> One trick that SOMETIMES helps:Â  Take a

 handheld

 >> VHF radio, remove the antenna and stick a

 paperclip into the

 >> center conductor of the antenna jack.Â  Hook

 headphones

 >> to the handheld radio.Â  Now start the

 aircraft and use

 >> the radio as a â€œtest wandâ€ and run it around

 the wiring

 >> to try and find the source.Â  This is not easy

 and takes

 >> some effort.

 >>> Bottom line:Â  Your noise is coming from

 your P

 >> leads and new tach.Â  Good luck.Â  Merry

 Christmas.

 >>> Mark Bitterlich

 >>>

 >>>

 >>> --- On Fri, 12/17/10, Scott Poehlmann<scott-p(at)texas.net>

 >> wrote:

 >>>> From: Scott Poehlmann<scott-p(at)texas.net>

 >>>> Subject: Re: RF interference

 >>>> To: yak-list(at)matronics.com

 >>>> Date: Friday, December 17, 2010, 9:03 PM

 >>>> -->Â Â Â Yak-List message

 posted by:

 >>>> Scott Poehlmann<scott-p(at)texas.net>

 >>>>

 >>>> Thanks Mark,

 >>>>

 >>>> I knew that you would have a great, step

 by step

 >> method.

 >>>> Went out to the hangar today: looks like

 the

 >> P-leads are

 >>>> the

 >>>> culprit--BOTH have the shielding detached

 from

 >> the

 >>>> connector and about 1

 >>>> cm of unshielded lead "hanging in the

 breeze".

 >> I'll spend

 >>>> some time

 >>>> tomorrow AM soldering the shielding to

 the

 >> connector (it

 >>>> appears that

 >>>> this has been done before and that the

 solder

 >> joints have

 >>>> failed...),

 >>>> and will advise if this doesn't fix the

 problem.

 >>>>

 >>>> Now for the next question: any ideas where

 to find

 >> a cover

 >>>> for the tach

 >>>> generator drive? I am running a Horizon

 digital

 >> tach (which

 >>>> takes its

 >>>> data from the mag--in fact it is wired

 into the

 >> back of the

 >>>> mag

 >>>> switch...), and I have no tach generator,

 just a

 >> big open

 >>>> fitting with a

 >>>> drive (and seal) at the bottom... Threaded

 on the

 >> outside,

 >>>> of course.

 >>>>

 >>>> Thanks again, and to everyone else who

 provided

 >>>> information. This list

 >>>> is a tremendous asset to the continued

 operation

 >> of these

 >>>> airplanes.

 >>>>

 >>>> Scott

 >>>>

 >>>> On 12-17-2010 10:15, Yak Pilot wrote:

 >>>>> -->Â  Â  Yak-List message

 >> posted by: Yak

 >>>> Pilot<yakplt(at)yahoo.com>

 >>>>> Do the following:

 >>>>>

 >>>>> Remove the plug from the Tach Gen and

 tie it

 >> back. Run

 >>>> the aircraft.Â  Does the noise go

 away?

 >> Then it is

 >>>> indeed your Tach Gen and it is most

 likely

 >> shielding at the

 >>>> Tach Generator plug itself.Â  Be

 careful

 >> taking this

 >>>> plug apart as it is common for the

 soldering on

 >> these wires

 >>>> to break.

 >>>>> If the noise does not go away, fly

 the

 >> airplane.

 >>>> Over the airport come to complete idle and

 then

 >> shut the

 >>>> mags off.Â  Both mags, turn them off.

 >>>>> You're now a glider.

 >>>>>

 >>>>> Did the noise go away?Â  If it

 did, then

 >> you have

 >>>> a MAG noise problem.Â  The mag noise

 filters

 >> will help,

 >>>> but before you go to that effort, look at

 the P

 >> leak plugs

 >>>> that go into the side of the mags.Â 

 It is

 >> very common

 >>>> for people to twist these plugs off during

 some

 >> kind of

 >>>> maint. action and in the process twist the

 shield

 >> right off

 >>>> the plug as well.Â  If the P Lead is

 >> unshielded you will

 >>>> have one huge amount of noise.

 >>>>> If the noise is still there even when

 you

 >> have

 >>>> performed these steps (whcih is highly

 unlikely)

 >> then you've

 >>>> got some other device radiating energy in

 the

 >>>> aircraft.Â  Start turning everything

 that you

 >> can off to

 >>>> try and identify it.

 >>>>> Suggestions have been made to see if

 it is

 >> coming in

 >>>> via the antenna or the power wiring.Â 

 I have

 >> posted

 >>>> these suggestions before, but it is

 something you

 >> do at the

 >>>> end of troubleshooting and not the

 >> beginning.Â  It is

 >>>> much easier to identify the noise source

 and

 >> eliminate it

 >>>> where it is coming from.Â  If you

 can't

 >> identify the

 >>>> noise and you are lucky enough to have it

 coming

 >> in via the

 >>>> power wires (again this is rare), a choke

 on the

 >> input power

 >>>> wiring can help eliminate the noise.Â 

 This

 >> can be as

 >>>> simple as a snap on torroid, or an

 expensive

 >> (purchased)

 >>>> filter, that is usually some sort of "Pi L

 brute

 >> force"

 >>>> filter consisting of two caps and an

 inductor.

 >>>> Usually, snap on torroids are just as

 effective

 >> and much

 >>>> cheaper.Â  Again though, noise coming

 in via

 >> the power

 >>>> wiring is rare.Â  It usually is coming

 in via

 >> the

 >>>> antenna, and that means you MUST eliminate

 the

 >> noise at it's

 >>>> source.

 >>>>> The tests described above will usually

 nail

 >> the

 >>>> problem in short order.

 >>>>> Mark Bitterlich

 >>>>>

 >>>>> p.s.Â  The reason I recommend

 shutting the

 >> mags

 >>>> off at idle in flight versus doing it on

 the

 >> ground is

 >>>> because the engine keeps wind-milling even

 with

 >> the mags

 >>>> off, and you can leave them off much

 longer while

 >> you are

 >>>> listening for radio noise and seeing if it

 goes

 >> away.

 >>>> Shutting the engine off with the mags and

 the

 >> engine

 >>>> windmilling with it at idle will not hurt

 >> anything, although

 >>>> the engine will cool off really fast, so

 when you

 >> turn the

 >>>> mags back on and the engine once again is

 >> actually

 >>>> "running", don't just cob the power to

 100%.

 >> Bring it

 >>>> in slowly.Â  Common sense applies.

 >>>>> --- On Thu, 12/16/10, Roger Kemp

 M.D.<viperdoc(at)mindspring.com>

 >>>> wrote:

 >>>>>> From: Roger Kemp M.D.<viperdoc(at)mindspring.com>

 >>>>>> Subject: RE: RF

 interference

 >>>>>> To: yak-list(at)matronics.com

 >>>>>> Date: Thursday, December 16, 2010,

 1:35

 >> PM

 >>>>>> -->Â  Â  Yak-List

 message

 >> posted by:

 >>>>>> "Roger Kemp M.D."<viperdoc(at)mindspring.com>

 >>>>>>

 >>>>>> Check the shielding on your Tac

 Generator.

 >> That is

 >>>> the most

 >>>>>> likely source

 >>>>>> for RPM related noise.

 >>>>>> Doc

 >>>>>>

 >>>>>> --

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