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luckymacy(at)comcast.net
Guest

Posted: Sat Jul 15, 2006 6:03 pm Post subject: Help needed: continued strobe noise & weak radio

I have two "comm" issues that I haven't  been able to debug to completion yet.  I'm using an Xcom 760 radio with their pre-made harness.



1) I still hear my strobes in my headset even when they are grounded with the radio ground and even when I put power noise filters on.  However, the Radio Shack noise filters reference on Bob's web site were reported to me to be no longer carried by them.  So I used the only ones I could find locally which were sold by Pep Boys and the capacitor was 4700 uF instead of 2200 uF like Radio Shack apparently was.



More specifically, the strobe noise is relatively faint until I select the Push to Talk button.  Then it gets pretty loud.  Some feedback going on there.  Looking for ideas from this list.



Should the capacitor specs have made a big difference on the effectiveness overall of the noise filter?  It made no measurable difference regardless of whether I installed it just before the radio or out at the strobe's power supply just before the AC +14v entered the power supply.  I even reversed direction of the filter and it didn't matter one iota.  Really bummed out about this turn of events since I thought they'd at least have made some observable difference based upon stuff in the archives.



2)  The second overall problem is that the radio still is reported to me by other pilots as weak when I get much beyond a couple of miles and breaks up in the pattern a lot.  I'm guessing it's because I can't put out enough consistent power to break their squelch consistently.  When on the actual ground taxiing around, if there's a crown or "hill" between me and another airplane on the ground forget it.  They can't hear me or vice  a versa.



When I check my radio with a handheld on the ground I seem to be just fine for the relatively close distances I've tried even when the plane is inside an open hangar and come in just as loud on the hand held as anyone else is.  It also doesn't matter whether or not the strobes are powered on or not as far as whether or not the range/strength improves.  ie, even with them off the lack of range doesn't improve.



I swapped the cable between the radio and the antenna and it made no difference.  I bought my antenna from Van's  but didn't do any kind of post install test besides checking it out with my comm radio and a hand held and it seemed fine at the time...



Instead of using RG-58 I bought two pre-made RG-400 cables.  What should the center conductor's resistance read end to end?  ~58 Ohms, right? My actual reading bounces all over the place no matter how stable I am in trying to read it. Strange.   Also, there doesn't seem to be a short between the center conductor and the plug itself when I check it with a multimeter so I'm guessing the plugs were installed correctly.



Things I have left to try is just buy a pre-made 12' RG-58 cable from radio shack and try it instead of the RG-400 cables.  Also, I don't have a spare comm antenna but I think RS carries a replacement 800 Mhz scanner antenna with the right BNC connector that I can just temporarily use just to see if makes any difference at all.  



Any ideas from the list?

Hopperdhh(at)aol.com
Guest

Posted: Sat Jul 15, 2006 7:38 pm Post subject: Help needed: continued strobe noise & weak radio

In a message dated 7/15/2006 10:05:43 P.M. Eastern Daylight Time,  luckymacy(at)comcast.net writes:

  	  Quote: 	
		  Instead    of using RG-58 I bought two pre-made RG-400 cables.  What should the    center conductor's resistance read end to end?  ~58 Ohms, right? My    actual reading bounces all over the place no matter how stable I am in trying    to read it. Strange.   Also, there doesn't seem to be a short    between the center conductor and the plug itself when I check it with a    multimeter so I'm guessing the plugs were installed  correctly.

	
 No, with a DC meter the cable should read very low resistance from end to  end on the center conductor.  You should measure an open from center  conductor to shield.  And you should measure a short from end to end on the  outer shield of the fittings.  It sounds like you may have a bad (loose)  connection.  The 50 ohms refers to the high frequency characteristic  impedance of the cable.  That is the ratio of voltage to current in the  cable is (or should be) 50 ohms while it is conducting RF.

  

  	  Quote: 	
		  

Things I have left to try is just buy a pre-made 12' RG-58 cable    from radio shack and try it instead of the RG-400 cables.  Also, I don't    have a spare comm antenna but I think RS carries a replacement 800 Mhz scanner    antenna with the right BNC connector that I can just temporarily use just to    see if makes any difference at all.  

	
 Forget trying to use the 800 MHz antenna on the VHF Aircraft Band -- not a  good idea at all.

  	  Quote: 	
		  

Any    ideas from the list?

	
 

  

  

 I recommend finding a ham operator with an MFJ-259B or similar type  instrument that will measure the SWR of your antenna system.  That is,  check out your feedline and antenna.  Try to determine if the antenna is OK  then check antenna and feedline together, etc.

  

 Make sure the antenna is grounded to the aircraft skin by measuring from  the coax fitting with the coax disconnected to the skin with a DC  ohmmeter.  You should measure a short.

  

 Hope this helps,

  

 Dan Hopper

 K9WEK

 RV-7A

Hopperdhh(at)aol.com
Guest

Posted: Sat Jul 15, 2006 7:41 pm Post subject: Help needed: continued strobe noise & weak radio

In a message dated 7/15/2006 10:05:43 P.M. Eastern Daylight Time,  luckymacy(at)comcast.net writes:

  	  Quote: 	
		  swapped    the cable between the radio and the antenna and it made no difference.  I    bought my antenna from Van's  but didn't do any kind of post install test    besides checking it out with my comm radio and a hand held and it seemed fine    at the time...

	


 

 It seems to me like I had to put some star washers between the antenna and  skin to make connection there.  The antenna must be grounded to the  aircraft skin.

  

 Dan Hopper

 RV-7A

fvalarm(at)rapidnet.net
Guest

Posted: Sat Jul 15, 2006 7:42 pm Post subject: Help needed: continued strobe noise & weak radio

Lucky,



I'm don't know the definitive answer to your problems but here are a couple

thoughts.  This problem will most certainly take some time and investigation

to solve.



Sounds like the radio is not transmitting at enough power.  If this is

caused by a bad cable, it can be tested for continuity with a handheld

ohmmeter but will not be 58 ohms. The center conductor should read almost 0

ohms end to end.  Also test it to see that there is NO conductivity

(infinite ohms) between the center conductor and the outer shield.  Do these

tests with both ends disconnected from the radio and antenna.  Repeat the

test for no continuity between the center and ground with the antenna

installed



If you need 2200uF and all you have is 4700uF, put two in series to yield

2350uF.  This will get you closer.



If when you key the mic you get more strobe noise, most likely you are

getting noise introduced via the activated mic line or through the radio

itself. The mic wiring should be checked for proper isolation. Check to see

that the mic jacks are NOT grounded at the jack.  Check to see that the mic

line is not run close and parallel to any wiring going to/from the strobe

power supply.



You might try to transmit with the same antenna and cable using a handheld

radio.  If the range improves, then the Xcom radio is suspect.  If the range

is the same, try the handheld with it's own antenna.  If the handheld and

it's own antenna is better, there is likely a problem with the aircraft

antenna.  Is the aircraft antenna on the belly or top?



I would think that these two problems are separate issues, but you never

know.



Bevan

RV7A finish kit.



 



--

FLYaDIVE(at)aol.com
Guest

Posted: Sun Jul 16, 2006 12:21 am Post subject: Help needed: continued strobe noise & weak radio

In a message dated 7/15/06 10:05:43 PM Eastern Daylight Time, 

luckymacy(at)comcast.net writes:

==========================================

Dear UN-Lucky:



Reading your post you seem to have answered your own questions.  I have 

inserted my comments within the body of your post.  Please read on ...

 	  Quote: 	
		   I have two "comm" issues that I haven't  been able to debug to completion 

yet.
	


 	  Quote: 	
		     I'm using an Xcom 760 radio with their pre-made harness.

  

  1) I still hear my strobes in my headset even when they are grounded with 

 the radio ground and even when I put power noise filters on.  However, the 

 Radio Shack noise filters reference on Bob's web site were reported to me 

to 
	


 	  Quote: 	
		   be no longer carried by them.  So I used the only ones I could find locally 

 which were sold by Pep Boys and the capacitor was 4700 uF instead of 2200 

uF 
	


 	  Quote: 	
		   like Radio Shack apparently was.

- - - - - - - - - -
	


[Barry] - Strobe ground and Radio ground?  I'm not sure what you are 

referring to here.  Can you elaborate a bit more?

BUT, if you are talking about using a SHIELDED wire as your ground ... The 

shield should be grounded ONLY at the STROBE and you should use two conductor 

and a shield wire.  

As for the value of the capacitor, in 99.9% of the noise cases concerning a 

DC circuit [our planes] the bigger the value the better. I really doubt if the 

filter was designed ONLY for a specific frequency

------------------------------------------------------------------------------

------------- 

 	  Quote: 	
		    

  More specifically, the strobe noise is relatively faint until I select the 

 Push to Talk button.  Then it gets pretty loud.  Some feedback going on 

there.
	


 	  Quote: 	
		     Looking for ideas from this list.

- - - - - - - - - - -
	


[Barry] Yup, sure sounds like the Ground for the PTT is the same Ground for 

the Strobe.  Here is where a problem may exist.  Reading from either side of 

the PTT to ground should NOT show continuity.  This is a general statement, each 

radio may be different but you would want to check this out and make sure the 

PTT runs all the way back to the radio and NOT to A/C ground.

-----------------------------------------------------------------------------

 	  Quote: 	
		    

  Should the capacitor specs have made a big difference on the effectiveness 

 overall of the noise filter?  It made no measurable difference regardless 

of 
	


 	  Quote: 	
		   whether I installed it just before the radio or out at the strobe's power 

 supply just before the AC +14v entered the power supply.  I even reversed 

 direction of the filter and it didn't matter one iota.  Really bummed out 

 about this turn of events since I thought they'd at least have made some 

 observable difference based upon stuff in the archives.

- - - - - - - - - -
	


[Barry] - QUESTIONS:  

How many leads does the filter have?

What are they labeled?

Most filters will have three of four leads.  They may be: (4 lead) Pos & Neg 

INPUT with Pos & Neg OUTPUT. Or, (3 lead) Pos & Neg INPUT with a Pos OUTPUT 

{common Ground/Neg}.

The filter should go ON the device that is making the noise ... STROBE.

But, you have to go back and check how you hooked up the GROUNDS.

I'm betting that:

1 - The filter is not right next to the strobe.

2 - The power leads are not shielded.

3 - The ground goes all the way back to the area of the radios.

------------------------------------------------------------------------------

-  

 	  Quote: 	
		    2)  The second overall problem is that the radio still is reported to me 

by 
	


 	  Quote: 	
		   other pilots as weak when I get much beyond a couple of miles and breaks up 

 in the pattern a lot.  I'm guessing it's because I can't put out enough 

 consistent power to break their squelch consistently.  When on the actual 

 ground taxiing around, if there's a crown or "hill" between me and another 

 airplane on the ground forget it.  They can't hear me or vice  a versa.

  

  When I check my radio with a handheld on the ground I seem to be just fine 

 for the relatively close distances I've tried even when the plane is inside 

 an open hangar and come in just as loud on the hand held as anyone else is. 

 
	


 	  Quote: 	
		   It also doesn't matter whether or not the strobes are powered on or not as 

 far as whether or not the range/strength improves.  ie, even with them off 

 the lack of range doesn't improve.

  

  I swapped the cable between the radio and the antenna and it made no 

 difference.  I bought my antenna from Van's  but didn't do any kind of post 

 install test besides checking it out with my comm radio and a hand held and 

 it seemed fine at the time...

- - - - - - - - - - - - 
	


[Barry] - What kind of antenna are you using and where is it mounted?

------------------------------------------------------------------------------

-------  

 	  Quote: 	
		    Instead of using RG-58 I bought two pre-made RG-400 cables.  What should 

the 
	


 	  Quote: 	
		   center conductor's resistance read end to end?  ~58 Ohms, right? My actual 

 reading bounces all over the place no matter how stable I am in trying to 

 read it. Strange.   Also, there doesn't seem to be a short between the 

center 
	


 	  Quote: 	
		   conductor and the plug itself when I check it with a multimeter so I'm 

 guessing the plugs were installed correctly.

  

  Things I have left to try is just buy a pre-made 12' RG-58 cable from 

radio 
	


 	  Quote: 	
		   shack and try it instead of the RG-400 cables.  Also, I don't have a spare 

 comm antenna but I think RS carries a replacement 800 Mhz scanner antenna 

 with the right BNC connector that I can just temporarily use just to see if 

 makes any difference at all.  

- - - - - - - - - - - - - - - -
	


[Barry] - YOU just answered your own question.  The RESISTANCE of a COAX when 

disconnected from both ends should read OPEN _ INFINITY between center 

conductor and shield.  It should read SHORT_ ZERO between one end shield and the 

other end shield.  It should also read SHORT_ ZERO between one end center 

conductor to other end center conductor.

As for the COAX, RG-400 is 75 ohm impeadance cable it is also a quad shield 

cable a VERY good cable but not suited for our needs.  We should be using RG-58 

or RG-58A/U. It works for us very well.  Oh, notice I used the term 

IMPEDANCE. This is an AC resistance and is NOT measured with an OHM Meter.

Concerning the RG-800 .... I am not familiar with it.  RG-58 is what you need 

to use.

As for the Radio Shack (Real $hit) pre-made COAX stay away from it.  I have 

seen so many problems in their assembly, wrong coax, poor connections and 

CRIMPS!  You do not want a crimped coax.



NO self-respecting RF Man will accept a CRIMPED coax.



Barry

"Chop'd Liver"

luckymacy(at)comcast.net
Guest

Posted: Sun Jul 16, 2006 4:09 am Post subject: Help needed: continued strobe noise & weak radio

My answers and corrections to your wrong guesses/assumptions below:

 [quote] 

-------------- Original message -------------- 

From: FLYaDIVE(at)aol.com 

 	  Quote: 	
		   --> AeroElectric-List message posted by: FLYaDIVE(at)aol.com 

 In a message dated 7/15/06 10:05:43 PM Eastern Daylight Time, 

 luckymacy(at)comcast.net writes: 

 ========================================== 

 Dear UN-Lucky: 

 Reading your post you seem to have answered your own questions. I have 

 inserted my comments within the body of your post. Please read on ... 

 > I have two "comm" issues that I haven't been able to debug to completion 

 yet. 

 > I'm using an Xcom 760 radio with their pre-made harness. 

 > 

 > 1) I still hear my strobes in my headset even when they are grounded with 

 > the radio ground and even when I put power noise filters on. However, the 

 > Radio Shack noise filters reference on Bob's web site were reported to me 

   to [b]> > be no longer carried by them. So I used the only ones I could find locally 

 > which were sold by Pep Boys and the capacitor was 4700 uF instead of 2200 

 uF 

 > like Radio Shack apparently was. 

 - - - - - - - - - - 

 [Barry] - Strobe ground and Radio ground? I'm not sure what you are 

 referring to here. Can you elaborate a bit more?  

Lucky:  My 2 strobe power supplies are installed at the wing tip and grounded to the wing spar locally.  Moving the grounds to back in the area where the rest of my electronics were grounded including the XCOM radio didn't have any affect. 

Also, disconnecting one strobe's power supply at a time didn't show that just one was the culprit.  They were both equal contributors.  Installing the audio noise filters out at the wing tips on the 14vdc input line just prior to the strobe power supply had no affect.  Installing one of those audio noise filters (a plastic box with an inductor and a capacitor) on the 14vdc input line to the xcom radio itself also had no affect.   

BTW, after I originally bought and installed the Xcom radio, they revised their drawing and FAQ section to REQUIRE owners install a 22,000 uF cap betwee the xcom and it's power source near the radio.  I didn't do that.  Couldn't locally find such cap.  

 	  Quote: 	
		   BUT, if you are talking about using a SHIELDED wire as your ground ... The 

 shield should be grounded ONLY at the STROBE and you should use two conductor 

 and a shield wire. 

 As for the value of the capacitor, in 99.9% of the noise cases concerning a 

 DC circuit [our planes] the bigger the value the better. I really doubt if the 

 filter was designed ONLY for a specific frequency 

 ------------------------------------------------------------------------------  

Lucky:  I used Van's pre-made wiring kit but I don't recall if the wiring to the strobes was shielded or not.  I'll check on that today to see if I or Van's made a mistake because there is NO evidence shielded wiring was used for the strobe power supply. It's been a long time since I hooked that up originally and haven't looked at that angle yet so details are very fuzzy.  The noise filter was marketed to address noise introduced into radios when the car's engine RPM is increased.  But pulling its case open revealed it's just the same 3 wire setup that Radio Shack was selling for while but with a different cap rating. 

 	  Quote: 	
		   ------------- 

 > 

 > More specifically, the strobe noise is relatively faint until I select the 

 > Push to Talk button. Then it gets pretty loud. Some feedback going on 

 there. 

 > Looking for ideas from this list. 

 - - - - - - - - - - - 

 [Barry] Yup, sure sounds like the Ground for the PTT is the same Ground for 

 the Strobe. Here is where a problem may exist. Reading from either side of 

 the PTT to ground should NOT show continuity. This is a general statement, each 

 radio may be different but you would want to check this out and make sure the 

 PTT runs all the way back to the radio and NOT to A/C ground. 

 -----------------------------------------------------------------------------  

Lucky:  I'll check it out today.  The original PTT switch came pre-wired with the radio harness but I cut it off to use a different switch already installed in my grip but just mirrored the pre-made setup. 

 	  Quote: 	
		   > 

 > Should the capacitor specs have made a big difference on the effectiveness 

 > overall of the noise filter? It made no measurable difference regardless 

 of 

 > whether I installed it just before the radio or out at the strobe's power 

 > supply just before the AC +14v entered the power supply. I even reversed 

 > direction of the filter and it didn't matter one iota. Really bummed out 

 > about this turn of events since I thought they'd at least have made some 

 > observable difference based upon stuff in the archives. 

 - - - - - - - - - - 

 [Barry] - QUESTIONS: 

 How many leads does the filter have? 

 What are they labeled? 

 Most filters will have three of four leads. They may be: (4 lead) Pos & Neg 

 INPUT with Pos & Neg OUTPUT. Or, (3 lead) Pos & Neg INPUT with a Pos OUTPUT 

 {common Ground/Neg}. 

 The filt  er sho uld go ON the device that is making the noise ... STROBE. 

 But, you have to go back and check how you hooked up the GROUNDS. 

 I'm betting that: 

 1 - The filter is not right next to the strobe. 

 2 - The power leads are not shielded. 

 3 - The ground goes all the way back to the area of the radios. 

 ------------------------------------------------------------------------------  

Lucky:  Filter has 3 leads.  A postive IN, a Positive OUT and a ground lead coming from the same physical side off the box as the Positive OUT lead.  It was installed literally adjacent to the strobes power supply's input voltage matching the filter's instructions with no affect and I reversed the filters Positive In/Out leads just for grins but again it made zero difference.  I put in on just before the radio too and it also made no difference.  The directions that came with it were assuming you were going to install it between a car radio and it's input voltage to clean up the input voltage.  Not somewhere else near the actual source of "noise". 

 	  Quote: 	
		   - 

 > 2) The second overall problem is that the radio still is reported to me 

 by 

 > other pilots as weak when I get much beyond a couple of miles and breaks up 

 > in the pattern a lot. I'm guessing it's because I can't put out enough 

 > consistent power to break their squelch consistently. When on the actual 

 > ground taxiing around, if there's a crown or "hill" between me and another 

 > airplane on the ground forget it. They can't hear me or vice a versa. 

 > 

 > When I check my radio with a handheld on the ground I seem to be just fine 

 > for the relatively close distances I've tried even when the plane is inside 

 > an open hangar and come in just as loud on the hand held as anyone else is. 

 > It also doesn't matter whether or not the strobes are powered on or not as 

 > far as whether or not the range/strength improve  s. ie,  even with them off 

 > the lack of range doesn't improve. 

 > 

 > I swapped the cable between the radio and the antenna and it made no 

 > difference. I bought my antenna from Van's but didn't do any kind of post 

 > install test besides checking it out with my comm radio and a hand held and 

 > it seemed fine at the time... 

 - - - - - - - - - - - - 

 [Barry] - What kind of antenna are you using and where is it mounted? 

 ------------------------------------------------------------------------------  

It's one of the bent which antennas that Van's sells.  Don't remember the brand.  Will look it over again today. 

 	  Quote: 	
		   ------- 

 > Instead of using RG-58 I bought two pre-made RG-400 cables. What should 

 the 

 > center conductor's resistance read end to end? ~58 Ohms, right? My actual 

 > reading bounces all over the place no matter how stable I am in trying to 

 > read it. Strange. Also, there doesn't seem to be a short between the 

 center 

 > conductor and the plug itself when I check it with a multimeter so I'm 

 > guessing the plugs were installed correctly. 

 > 

 > Things I have left to try is just buy a pre-made 12' RG-58 cable from 

 radio 

 > shack and try it instead of the RG-400 cables. Also, I don't have a spare 

 > comm antenna but I think RS carries a replacement 800 Mhz scanner antenna 

 > with the right BNC connector that I can just temporarily use just to see if 

 > makes any difference at all. 

 - - - - - - - - - - -   - - -  - - 

 [Barry] - YOU just answered your own question. The RESISTANCE of a COAX when 

 disconnected from both ends should read OPEN _ INFINITY between center 

 conductor and shield. It should read SHORT_ ZERO between one end shield and the 

 other end shield. It should also read SHORT_ ZERO between one end center 

 conductor to other end center conductor. 

 As for the COAX, RG-400 is 75 ohm impeadance cable it is also a quad shield 

 cable a VERY good cable but not suited for our needs. We should be using RG-58 

 or RG-58A/U. It works for us very well. Oh, notice I used the term 

 IMPEDANCE. This is an AC resistance and is NOT measured with an OHM Meter. 

 Concerning the RG-800 .... I am not familiar with it. RG-58 is what you need 

 to use.  

Lucky:  RG-800?  Why did you bring that up?  Also, I think RG-400 is RF the same as RG-58 but better shielded as you point out and it should be superior to RG-58 if cable flexibility isn't an issue.  It should NOT be the problem BUT I threw out using RS pre-made RG-58 just to rule out some manufactering/fabrication of the pre-made RG-400 cables. 

Thanks for the ideas and feedback, 

Lucky  atroni

luckymacy(at)comcast.net
Guest

Posted: Sun Jul 16, 2006 4:12 am Post subject: Help needed: continued strobe noise & weak radio

 

  

  	  Quote: 	
		  -------------- Original message -------------- 

From: Hopperdhh(at)aol.com 

  In a message dated 7/15/2006 10:05:43 P.M. Eastern Daylight Time, luckymacy(at)comcast.net writes:

  	  Quote: 	
		  Instead of using RG-58 I bought two pre-made RG-400 cables.  What should the center conductor's resistance read end to end?  ~58 Ohms, right? My actual reading bounces all over the place no matter how stable I am in trying to read it. Strange.   Also, there doesn't seem to be a short between the center conductor and the plug itself when I check it with a multimeter so I'm guessing the plugs were installed correctly.

	
 No, with a DC meter the cable should read very low resistance from end to end on the center conductor.  You should measure an open from center conductor to shield.  And you should measure a short from end to end on the outer shield of the fittings.  It sounds like you may have a bad (loose) connection.  The 50 ohms refers to the high frequency characteristic impedance of the cable.  That is the ratio of voltage to current in the cable is (or should be) 50 ohms while it is conducting RF.

 

 

 Lucky:  Yep, what was I thinking when I wrote that.  The resistance from tip to tip is basically zero and both sides off the cable show open between the center conductor's tip and the shield.

  

 Also, I mention using this cable not because it should work well but to use ANY antenna temporarily that's isolated from the airframe to help in figuring out of the current one is part of the problem.

  

  	  Quote: 	
		  

Things I have left to try is just buy a pre-made 12' RG-58 cable from radio shack and try it instead of the RG-400 cables.  Also, I don't have a spare comm antenna but I think RS carries a replacement 800 Mhz scanner antenna with the right BNC connector that I can just temporarily use just to see if makes any difference at all.  

	
 Forget trying to use the 800 MHz antenna on the VHF Aircraft Band -- not a good idea at all.

  	  Quote: 	
		  

Any ideas from the list?

	
  

  

  

 I recommend finding a ham operator with an MFJ-259B or similar type instrument that will measure the SWR of your antenna system.  That is, check out your feedline and antenna.  Try to determine if the antenna is OK then check antenna and feedline together, etc.

  

 Make sure the antenna is grounded to the aircraft skin by measuring from the coax fitting with the coax disconnected to the skin with a DC ohmmeter.  You should measure a short.

  

 Hope this helps,

  

 Dan Hopper

 K9WEK

 RV-7A

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Sun Jul 16, 2006 8:00 am Post subject: Help needed: continued strobe noise & weak radio

On Jul 15, 2006, at 9:54 PM, lucky wrote:



 	  Quote: 	
		   



 I have two "comm" issues that I haven't  been able to debug to  

 completion yet.  I'm using an Xcom 760 radio with their pre-made  

 harness.



 1) I still hear my strobes in my headset even when they are  

 grounded with the radio ground and even when I put power noise  

 filters on.  However, the Radio Shack noise filters reference on  

 Bob's web site were reported to me to be no longer carried by  

 them.  So I used the only ones I could find locally which were sold  

 by Pep Boys and the capacitor was 4700 uF instead of 2200 uF like  

 Radio Shack apparently was.


	


Make sure your mic and headphone jacks are insulated from the  

airframe. Use fiber insulating washers between the jack and the panel.



The 4700 uF cap is fine as it will have about twice the filtering of  

a 2200 uF cap. OTOH, if all your filter is is a capacitor, it will  

have almost no effect. You also need a choke in series with the power  

lead like this:



fuseblock ---------[choke]----+-------->[radio]

                               |

                           [capacitor]

                               |

                               v

                            ground



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

luckymacy(at)comcast.net
Guest

Posted: Sun Jul 16, 2006 5:30 pm Post subject: Help needed: continued strobe noise & weak radio

I'll take a look at them next time I get out there and I think the mike and headphone jacks are fitted correctly.  If they weren't, wouldn't I have a problem all the time? In fact, would they work at all?  For example, even when using the radio's internal VOX intercom system wouldn't I get a bad signal and wouldn't there be a lot of noise from other components whey they are turned on?  The VOX works very well (except that when the strobes are on, yes, you hear them loud and clear as well).  I haven't noticed any other electrical component causing a problem that's audible and the radio itself hasn't seemed to bother any other electrical system.

 Today I temporarily installed my ELTs antenna on my radio and it didn't help or seem to hurt from what I could tell on the ground experimenting.

 [quote]-------------- Original message -------------- 

From: Brian Lloyd <brian-yak(at)lloyd.com> 

[quote] --> AeroElectric-List message posted by: Brian Lloyd 

 On Jul 15, 2006, at 9:54 PM, lucky wrote: 

 > --> AeroElectric-List message posted by: luckymacy(at)comcast.net (lucky) 

 > 

 > I have two "comm" issues that I haven't been able to debug to 

 > completion yet. I'm using an Xcom 760 radio with their pre-made 

 > harness. 

 > 

 > 1) I still hear my strobes in my headset even when they are 

 > grounded with the radio ground and even when I put power noise 

 > filters on. However, the Radio Shack noise filters reference on 

 > Bob's web site were reported to me to be no longer carried by 

 > them. So I used the only   ones I  could find locally which were sold 

 > by Pep Boys and the capacitor was 4700 uF instead of 2200 uF like 

 > Radio Shack apparently was. 

 Make sure your mic and headphone jacks are insulated from the 

 airframe. Use fiber insulating washers between the jack and the panel. 

 The 4700 uF cap is fine as it will have about twice the filtering of 

 a 2200 uF cap. OTOH, if all your filter is is a capacitor, it will 

 have almost no effect. You also need a choke in series with the power 

 lead like this: 

 fuseblock ---------[choke]----+-------->[radio] 

 | 

 [capacitor] 

 | 

 v 

 ground 

 Brian Lloyd 361 Catterline Way 

 brian-yak AT lloyd DOT com Folsom, CA 95630 

 +1.916.367.2131 (voice) +1.270.912.0788 (fax) 

 I fly because it releases my mind from the tyranny of petty things . . . 

 — Antoine   de Sa   http:

Hopperdhh(at)aol.com
Guest

Posted: Sun Jul 16, 2006 6:14 pm Post subject: Help needed: continued strobe noise & weak radio

Lucky,

  

 Did you check to see if the antenna ground is grounded to the skin?

  

 Dan

europa flugzeug fabrik

Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA

Posted: Sun Jul 16, 2006 7:45 pm Post subject: Re: Help needed: continued strobe noise & weak radio

This sounds like two separate problems. I wouldnâ€™t discount the fact that the strobe noise heard in audio is coming from the 14V power supply to the comm.



The hint is in more noise heard when you xmit, but youâ€™re listening to sidetone, not regular receive audio.  That circuit (potentially part of what modulates the RF signal when you talk) may be fed by a power-supply circuit within the XCOM which is inadequately filtered.  Nor is the power supply for receive all that great either, as described.

 

So, add what XCOM forgot. A external filter needs an inductor (choke), in addition to a capacitor, as explained by Brian.  If the Pep Boys item has a choke, it may not be adequate.  A big capacitor alone cannot filter high-frequency or sharp-spike noise too well, nor will value matter that much.  I fixed a noisy (via alternator) audio panel with a choke from a bunch of wound toroid cores from a surplus electronic junk store.  I used the one which worked best, probably one with a lot of turns.  Added a cap of arbitrary value (the one in the audio panel wasnâ€™t very big), and all was well.  Itâ€™s possible a toroid donut is superior to a big transformer-like choke, which I think Radio Shackâ€™s version was like.



Antennas are reciprocal, and you donâ€™t say how well you receive.  If you can receive within spec, you can xmit.  At around 3500 AGL, with reasonably flat terrain in between, you should hear airliners gettinâ€™ vectored down low at a big airport about 100 miles away.  Even 75 is passable, so then the problem is not in coax or antenna.  Leaving the XCOM as culprit on weak xmit.



RG-400 is 50-ohm, and will work fine.  Though not superior enough (except longevity in service) for fixing VHF problems.



Fred F.

europa flugzeug fabrik

Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA

Posted: Sun Jul 16, 2006 7:55 pm Post subject: Re: Help needed: continued strobe noise & weak radio

 	  FLYaDIVE(at)aol.com wrote: 	
		  CRIMPS!  You do not want a crimped coax.



NO self-respecting RF Man will accept a CRIMPED coax.

	


Why do you say that?   You mean a soldered,  and hex-nut BNC connector fashioned by a homebuilder wil be better?  On avg, don't think so.



Fred F.

europa flugzeug fabrik

Joined: 13 Feb 2006
Posts: 65
Location: North Coast, USA

Posted: Sun Jul 16, 2006 8:00 pm Post subject: Re: Help needed: continued strobe noise & weak radio

 	  luckymacy(at)comcast.net wrote: 	
		  BTW, after I originally bought and installed the Xcom radio, they revised their drawing and FAQ section to REQUIRE owners install a 22,000 uF cap betwee the xcom and it's power source near the radio. 	


If Microair said that's a fix, they're admitting to bad design of the XCOM box.  At high freq, diminishing returns, that big, I propose.  Simpler ways to fix.



Fred F.

fvalarm(at)rapidnet.net
Guest

Posted: Sun Jul 16, 2006 9:51 pm Post subject: Help needed: continued strobe noise & weak radio

Lucky,



It would be interesting to power the strobes from a separate battery with no

shared ground to isolate the path of noise source.



Bevan 



--

FLYaDIVE(at)aol.com
Guest

Posted: Mon Jul 17, 2006 2:48 am Post subject: Help needed: continued strobe noise & weak radio

In a message dated 7/16/06 8:11:43 AM Eastern Daylight Time, 

luckymacy(at)comcast.net writes:



 	  Quote: 	
		   Lucky:  I used Van's pre-made wiring kit but I don't recall if the wiring 

to 
	


 	  Quote: 	
		   the strobes was shielded or not. 

======================================
	


Lucky:



I think you found the problem.  I say that because of the above statement 

about the pre-made harness.  If they are running the strobe's wires right along 

side the wires for your other lights AND if they are not shielded then it would 

be very easy for the other wires to pick up the noise from the strobes.  

Try running a separate SHIELDED pair of wires and ground the shield ONLY at 

the strobe.  The shielded pair should have three wires ... B+. Neg and SHIELD.  

The Neg is grounded at both ends, while the shield is only at the strobe.  I 

would still use the filter, just for S&Gs.  Run the strobe wires away from the 

other wires.



I have a similar strobe system as you with the power supplies.  The strobes 

mounted at the wing tips and tail; three power supplies.  I found that there is 

a small amount of noise from the tail strobe.  I know I can get rid of it 

with an RS type filter, but it is on a GA aircraft so I'm not allowed to use RS 

or Lowe's aviation components 



You did say you tried mounting the filter at each location, Strobe and Radio. 

 Another thing to check and I have not seen it mentioned is LEAD LENGTH.  You 

must keep the leads as short as possible between the filter and the strobe.  

Still another trick you may want to try is to install a ferrite bead 

(tolroid) on the B+ lead, close to the strobe.  

Me still being a bit redundant, make sure you have extra clean ground 

connections; aluminum is not a good material for electrical connections. 



Well, beyond all the techniques and trick I mentioned in this post and my 

other.  My other offer would be ... Where are you located, maybe we could meet 

up?  I'd bet dollars to doughnuts I can solve your problem.  I'd be glad to help.



Barry

"Chop'd Liver"

FLYaDIVE(at)aol.com
Guest

Posted: Mon Jul 17, 2006 3:03 am Post subject: Help needed: continued strobe noise & weak radio

In a message dated 7/17/06 12:00:46 AM Eastern Daylight Time, 

n3eu(at)comcast.net writes:

 	  Quote: 	
		   FLYaDIVE(at)aol.com wrote:

  > CRIMPS!  You do not want a crimped coax.

  > 

  > NO self-respecting RF Man will accept a CRIMPED coax.

  > 

  Why do you say that?   You mean a soldered,  and hex-nut BNC connector 

 fashioned by a homebuilder wil be better?  On avg, don't think so.

  Fred F.

=================================

Yup!  Fred ...  Soldered, Hex Nut BNC connector.  As far as who fashions it 

.. Why not the homebuilder?  After all the homebuilder was not born knowing 

how to rivet, why not just learn how to do a proper BNC connection.  They are 

SOOooooo much better, water proof (or at least highly resistant), vibration 

proof, dust proof and of course a damn good RF electrical connection.  AND you can 

do a field repair on them.  Can't do that on crimp crap.

The BNC was born out of the SO & PL fittings.  It is better for maintaining 

the impedance of the cable especially at low power VHF frequencies.  The higher 

power, higher frequency version is the Type N.

Barry

"Chop'd Liver"

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Mon Jul 17, 2006 3:36 am Post subject: Help needed: continued strobe noise & weak radio

On Jul 16, 2006, at 9:25 PM, lucky wrote:



 	  Quote: 	
		   I'll take a look at them next time I get out there and I think the  

 mike and headphone jacks are fitted correctly.  If they weren't,  

 wouldn't I have a problem all the time? In fact, would they work at  

 all?


	


Yes, but the problem of the grounded mic jacks is that noise from  

other audio sources gets impressed on the mic audio.



 	  Quote: 	
		   For example, even when using the radio's internal VOX intercom  

 system wouldn't I get a bad signal and wouldn't there be a lot of  

 noise from other components whey they are turned on?  The VOX works  

 very well (except that when the strobes are on, yes, you hear them  

 loud and clear as well).


	


This is why I think you have a problem with your mic jacks being  

grounded.



 	  Quote: 	
		   I haven't noticed any other electrical component causing a problem  

 that's audible and the radio itself hasn't seemed to bother any  

 other electrical system.


	


Most other devices don't generate AC at audio frequencies in the  

grounding system.



Solve the problem of the bad audio first. After you deal with that  

and set the modulation levels correctly you can go from there.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Mon Jul 17, 2006 3:55 am Post subject: Help needed: continued strobe noise & weak radio

On Jul 17, 2006, at 6:37 AM, FLYaDIVE(at)aol.com wrote:

 	  Quote: 	

 In a message dated 7/16/06 8:11:43 AM Eastern Daylight Time,

 luckymacy(at)comcast.net writes:

> Lucky:  I used Van's pre-made wiring kit but I don't recall if the  

> wiring

 to

> the strobes was shielded or not.

 ======================================

 Lucky:

 I think you found the problem.  I say that because of the above  

 statement

 about the pre-made harness.  If they are running the strobe's wires  

 right along

 side the wires for your other lights AND if they are not shielded  

 then it would

 be very easy for the other wires to pick up the noise from the  

 strobes.

 Try running a separate SHIELDED pair of wires and ground the shield  

 ONLY at

 the strobe.  The shielded pair should have three wires ... B+. Neg  

 and SHIELD.

 The Neg is grounded at both ends, while the shield is only at the  

 strobe.  I

 would still use the filter, just for S&Gs.  Run the strobe wires  

 away from the

 other wires.

Barry, you keep making statements like this but I am not sure you  

have really thought through what you are saying.

When you run two wires in parallel there are two coupling modes:  

capacitive and inductive. When impedances are very high (it is  

difficult to get current to flow) then capacitive coupling dominates.  

When impedances are very low, as in power circuits, coupling is  

inductive, with the current in one wire inducing a current in the  

other wire by magnetic (inductive) coupling.

The problem with non-magnetic braid-type shielding is that it does  

almost nothing for inductive coupling. The magnetic lines of force go  

right through the shielding and induce currents in the shielded  

conductor just as if the shield wasn't there. That is why shielding  

on the alternator 'B' lead is useless to reduce noise. So you aren't  

going to fix noise from your strobe power supply getting into your  

other power wiring with a nonmagnetic shielding braid.

BTW, a shielding braid grounded at only one end is an electrostatic  

shield and only works to reduce capacitive coupling.

If the problem is inductive coupling between wires there are only two  

solutions:

1. separation;

2. the use of a magnetic shielding material like mu-metal.

If you have a severe inductive coupling problem and you can't get  

separation you can get magnetic shielding braid and sheets to help  

fix the problem. I used that to solve a problem with the motor in my  

T&B affecting my compass in my RV-4.

Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Mon Jul 17, 2006 3:57 am Post subject: Help needed: continued strobe noise & weak radio

On Jul 16, 2006, at 11:55 PM, europa flugzeug fabrik wrote:

 	  Quote: 	

 <n3eu(at)comcast.net>

 FLYaDIVE(at)aol.com wrote:

> CRIMPS!  You do not want a crimped coax.

>

> NO self-respecting RF Man will accept a CRIMPED coax.

Crimped connectors on cables tend to be better than hand-constructed  

and soldered cables. They last longer. A crimped connector with  

adhesive heat-shrink over is just about the best, most long-lived  

cable connection you can make. You learn stuff like this very quickly  

on a boat.

Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

FLYaDIVE(at)aol.com
Guest

Posted: Wed Jul 19, 2006 2:59 am Post subject: Help needed: continued strobe noise & weak radio

In a message dated 7/17/2006 7:59:52 AM Eastern Standard Time, brian-yak(at)lloyd.com writes:

  	  Quote: 	
		  >> Lucky:  I used Van's pre-made wiring kit but I don't recall if the  

 	  Quote: 	
		  > wiring

 to

> the strobes was shielded or not.

 ======================================

 Lucky:

 I think you found the problem.  I say that because of the above  

 statement about the pre-made harness.  If they are running the strobe's wires  

 right along side the wires for your other lights AND if they are not shielded  

 then it would  be very easy for the other wires to pick up the noise from the  

 strobes.

 Try running a separate SHIELDED pair of wires and ground the shield  

 ONLY at  the strobe.  The shielded pair should have three wires ... B+. Neg  

 and SHIELD.

 The Neg is grounded at both ends, while the shield is only at the  

 strobe.  I  would still use the filter, just for S&Gs.  Run the strobe wires  

 away from the  other wires.

Barry, you keep making statements like this but I am not sure you  

have really thought through what you are saying.

When you run two wires in parallel there are two coupling modes:  

capacitive and inductive. When impedances are very high (it is  

difficult to get current to flow) then capacitive coupling dominates.  

When impedances are very low, as in power circuits, coupling is  

inductive, with the current in one wire inducing a current in the  

other wire by magnetic (inductive) coupling. 	

 Brian:

 I make these statements because I know they work.

 As for Inductive / capacitive coupling.  We are talking DC circuits with Noise in the AUDIO frequency range.  

 As the saying goes: K.I.S.S. M.E. All this stuff about capacitive and inductive coupling is not an issue in a simple noise problem as we are discussing here.  AND what the heck is "NON-MAGNETIC BRAID-TYPE SHIELDING"?  Do you really expect people to go out looking for "mu-metal"?  ALL the braid used on any electrical circuit on our planes is NONMAGNETIC .. It is made of COPPER WIRE.  Copper is non magnetic the last time I checked.  Again K.I.S.S. M.E. is the word of the day.

 Electronics is simple, it is really!  All these boog-a-boo statements only confuses the non-electrical types amongst us.  The only thing they need to know is how to remove the noise.  Again that goes back to the basics of noise, and breaking it down into DC and AC ... AC goes one step further (Audio Frequencies [AF] and Radio Frequencies [RF]).  

 Basics:

 AF Noise - Shield and Ground at the source [This is why the Mic & Phone lines use insulating washers at the jacks and ground at the audio panel or radios.]

 RF Noise - Shield and Ground at both ends.  [Here is where exceptions come into play - Some times the grounding is done through a capacitor.  BUT we are dealing with AF Noise not RF so I'm not going to try to confuse people out there.]

 Let the manufacture of the wire worry about resistance of 1000 Ft and the capacitive coupling / inductive coupling at AF & RF.  The ONLY thing that would be of interest to our noise plagued brevien is the Percentage of Braid.  You did not say anything about that!  Yet again as long as you use Mil-Spec wire the percentage of braid is acceptable and again our brevien does not have to be concerned.

 As for the Separation of wires .... I did address that with my very first statement to Lucky; read above.

 I would suggest that all the AF noise (strobe noise) we are discussing be approached as I described AND then if the noise still exists just add another ground t=at the other end of the shield.  It is MUCH easier to ADD a ground than to remove a ground.

 Barry

 "Chop'd Liver"

 ==================================================================================

  	  Quote: 	

The problem with non-magnetic braid-type shielding is that it does  

almost nothing for inductive coupling. The magnetic lines of force go  

right through the shielding and induce currents in the shielded  

conductor just as if the shield wasn't there. That is why shielding  

on the alternator 'B' lead is useless to reduce noise. So you aren't  

going to fix noise from your strobe power supply getting into your  

other power wiring with a nonmagnetic shielding braid.

BTW, a shielding braid grounded at only one end is an electrostatic  

shield and only works to reduce capacitive coupling.

If the problem is inductive coupling between wires there are only two  

solutions:

1. separation;

2. the use of a magnetic shielding material like mu-metal.

If you have a severe inductive coupling problem and you can't get  

separation you can get magnetic shielding braid and sheets to help  

fix the problem. I used that to solve a problem with the motor in my  

T&B affecting my compass in my RV-4.

Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)

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