Matronics Email Lists :: View topic - COM radio/intercom wiring problem...

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

COM radio/intercom wiring problem...

Matronics Email Lists Forum Index -> AeroElectric-List

View previous topic :: View next topic

Author Message

mburbidg(at)gmail.com
Guest

Posted: Sat Jul 27, 2013 4:00 pm Post subject: COM radio/intercom wiring problem...

I'm trying to chase down a problem with my Radio (Garmin SL-40) Intercom (Flightcom 403) wiring. One of the strange behaviors that I don't understand is when I push the PTT to transmit on a common unicom frequency such as 122.7, the ammeter pegs at -40 amps. When I transmit on one of the maintenance frequencies such as 135.85, it only deflects negative 1-2 amps. But the radio is transmitting, I can hear on my handheld.



My ammeter is a shunt type ammeter and seems to work correctly in indicating positive (discharge)  loads for other equipment. What would make it indicate in the negative directions. This is using just the battery. i.e. engine not running.



The situation is that I'm trying to debug my initial wiring, so the setup has never worked.



Thanks for any hints.



Michael-

mburbidg(at)gmail.com
Guest

Posted: Sat Jul 27, 2013 4:29 pm Post subject: COM radio/intercom wiring problem...

I should note that the ammeter shunt is measuring alternator current. It is installed as in the Z-11 electrical system, between the starter contractor and the "b" lead on the alternator.



This could very well be expected behavior when on battery only.



Michael-



On Jul 27, 2013, at 4:59 PM, Michael Burbidge <mburbidg(at)gmail.com> wrote:



 	  Quote: 	
		   

 

 I'm trying to chase down a problem with my Radio (Garmin SL-40) Intercom (Flightcom 403) wiring. One of the strange behaviors that I don't understand is when I push the PTT to transmit on a common unicom frequency such as 122.7, the ammeter pegs at -40 amps. When I transmit on one of the maintenance frequencies such as 135.85, it only deflects negative 1-2 amps. But the radio is transmitting, I can hear on my handheld.

 

 My ammeter is a shunt type ammeter and seems to work correctly in indicating positive (discharge)  loads for other equipment. What would make it indicate in the negative directions. This is using just the battery. i.e. engine not running.

 

 The situation is that I'm trying to debug my initial wiring, so the setup has never worked.

 

 Thanks for any hints.

 

 Michael-

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jul 27, 2013 7:32 pm Post subject: COM radio/intercom wiring problem...

At 06:59 PM 7/27/2013, you wrote:

 	  Quote: 	
		  



I'm trying to chase down a problem with my Radio (Garmin SL-40) 

Intercom (Flightcom 403) wiring. One of the strange behaviors that I 

don't understand is when I push the PTT to transmit on a common 

unicom frequency such as 122.7, the ammeter pegs at -40 amps. When I 

transmit on one of the maintenance frequencies such as 135.85, it 

only deflects negative 1-2 amps. But the radio is transmitting, I 

can hear on my handheld.



My ammeter is a shunt type ammeter and seems to work correctly in 

indicating positive (discharge)  loads for other equipment. What 

would make it indicate in the negative directions. This is using 

just the battery. i.e. engine not running.



The situation is that I'm trying to debug my initial wiring, so the 

setup has never worked.


	




   You didn't say but I'm betting your ammeter is

   the one Van's sells . . . minus 40 - zero - plus

   40?



   I have one of those things laying around here somewhere.

   I think I reported to the List after I bought it that

   the instrument was very vulnerable to strong RF

   in the cockpit.



   What kind of airplane and where is your antenna

   located? Have you checked VSWR on the antenna

   over the vhf comm range?

   Bob . . .

billp(at)wwpc.com
Guest

Posted: Sat Jul 27, 2013 8:15 pm Post subject: COM radio/intercom wiring problem...

40 Amps is 480 watts at 14V. That's a lot for an aircraft radio to pull. It's an 8 watt transmitter and just keying the mic with no modulation it would be a fraction of that (it's an AM transmitter). The radio has an internal 7A fuse and the installation manual says to use a 5A external fuse or breaker.

I'm thinkin' there's something wonkie with the ammeter or the grounding for the avionics or the meter electronics.

Bill

Sent from my iPad

On Jul 27, 2013, at 8:32 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

 	  Quote: 	

 At 06:59 PM 7/27/2013, you wrote:

> 

> 

> I'm trying to chase down a problem with my Radio (Garmin SL-40) Intercom (Flightcom 403) wiring. One of the strange behaviors that I don't understand is when I push the PTT to transmit on a common unicom frequency such as 122.7, the ammeter pegs at -40 amps. When I transmit on one of the maintenance frequencies such as 135.85, it only deflects negative 1-2 amps. But the radio is transmitting, I can hear on my handheld.

> 

> My ammeter is a shunt type ammeter and seems to work correctly in indicating positive (discharge)  loads for other equipment. What would make it indicate in the negative directions. This is using just the battery. i.e. engine not running.

> 

> The situation is that I'm trying to debug my initial wiring, so the setup has never worked.

  You didn't say but I'm betting your ammeter is

  the one Van's sells . . . minus 40 - zero - plus

  40?

  I have one of those things laying around here somewhere.

  I think I reported to the List after I bought it that

  the instrument was very vulnerable to strong RF

  in the cockpit.

  What kind of airplane and where is your antenna

  located? Have you checked VSWR on the antenna

  over the vhf comm range?

  Bob . . .

mburbidg(at)gmail.com
Guest

Posted: Sat Jul 27, 2013 8:18 pm Post subject: COM radio/intercom wiring problem...

Yes, my ammeter is the Vans ammeter.

My airplane is an RV-9A. My COM antenna is mounted on the bottom of the airplane, approximately under where the left leg of the pilot is when sitting in the airplane. The antenna is from Delta Pop Aviation. The coax cable is RG400 from B&C.

I have not checked the VSWR on the antenna. I see your book gives some instructions on how to do that.

The airplane is currently in my garage. Would that "focus" the RF energy more than being out in the open?

Thanks,

Michael-

On Jul 27, 2013, at 8:32 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

 	  Quote: 	

 At 06:59 PM 7/27/2013, you wrote:

> 

> 

> I'm trying to chase down a problem with my Radio (Garmin SL-40) Intercom (Flightcom 403) wiring. One of the strange behaviors that I don't understand is when I push the PTT to transmit on a common unicom frequency such as 122.7, the ammeter pegs at -40 amps. When I transmit on one of the maintenance frequencies such as 135.85, it only deflects negative 1-2 amps. But the radio is transmitting, I can hear on my handheld.

> 

> My ammeter is a shunt type ammeter and seems to work correctly in indicating positive (discharge)  loads for other equipment. What would make it indicate in the negative directions. This is using just the battery. i.e. engine not running.

> 

> The situation is that I'm trying to debug my initial wiring, so the setup has never worked.

  You didn't say but I'm betting your ammeter is

  the one Van's sells . . . minus 40 - zero - plus

  40?

  I have one of those things laying around here somewhere.

  I think I reported to the List after I bought it that

  the instrument was very vulnerable to strong RF

  in the cockpit.

  What kind of airplane and where is your antenna

  located? Have you checked VSWR on the antenna

  over the vhf comm range?

  Bob . . .

peter(at)sportingaero.com
Guest

Posted: Sun Jul 28, 2013 10:57 am Post subject: COM radio/intercom wiring problem...

Several of the gauges sold by Van's are susceptible to interference from 

radio transmissions, particularly manifold pressure and amps. Probably 

not worth the effort to determine how/why it happens...



Peter



On 28/07/2013 05:17, Michael Burbidge wrote:

 	  Quote: 	
		   



 Yes, my ammeter is the Vans ammeter.



 My airplane is an RV-9A. My COM antenna is mounted on the bottom of the airplane, approximately under where the left leg of the pilot is when sitting in the airplane. The antenna is from Delta Pop Aviation. The coax cable is RG400 from B&C.



 I have not checked the VSWR on the antenna. I see your book gives some instructions on how to do that.



 The airplane is currently in my garage. Would that "focus" the RF energy more than being out in the open?



 Thanks,

 Michael-

 On Jul 27, 2013, at 8:32 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:



> 

>

> At 06:59 PM 7/27/2013, you wrote:

>> 

>>

>> I'm trying to chase down a problem with my Radio (Garmin SL-40) Intercom (Flightcom 403) wiring. One of the strange behaviors that I don't understand is when I push the PTT to transmit on a common unicom frequency such as 122.7, the ammeter pegs at -40 amps. When I transmit on one of the maintenance frequencies such as 135.85, it only deflects negative 1-2 amps. But the radio is transmitting, I can hear on my handheld.

>>

>> My ammeter is a shunt type ammeter and seems to work correctly in indicating positive (discharge)  loads for other equipment. What would make it indicate in the negative directions. This is using just the battery. i.e. engine not running.

>>

>> The situation is that I'm trying to debug my initial wiring, so the setup has never worked.

>

>   You didn't say but I'm betting your ammeter is

>   the one Van's sells . . . minus 40 - zero - plus

>   40?

>

>   I have one of those things laying around here somewhere.

>   I think I reported to the List after I bought it that

>   the instrument was very vulnerable to strong RF

>   in the cockpit.

>

>   What kind of airplane and where is your antenna

>   located? Have you checked VSWR on the antenna

>   over the vhf comm range?

>   Bob . . .

>

>

mburbidg(at)gmail.com
Guest

Posted: Sun Jul 28, 2013 11:42 am Post subject: COM radio/intercom wiring problem...

I hadn't noticed it, but the manifold pressure gauge, is also deflecting a good deal during radio transmission. I guess that's what I get for trying to be frugal with my instrumentation. I was alarmed by the ammeter deflection. But everything seems to be working otherwise, and there is no smoke or blown fuses, so I'm going to assume that this explains the ammeter deflection.



Michael-

On Jul 28, 2013, at 11:56 AM, Peter Pengilly <peter(at)sportingaero.com> wrote:



 	  Quote: 	
		   

 

 Several of the gauges sold by Van's are susceptible to interference from radio transmissions, particularly manifold pressure and amps. Probably not worth the effort to determine how/why it happens...

 

 Peter

 

 On 28/07/2013 05:17, Michael Burbidge wrote:

> 

> 

> Yes, my ammeter is the Vans ammeter.

> 

> My airplane is an RV-9A. My COM antenna is mounted on the bottom of the airplane, approximately under where the left leg of the pilot is when sitting in the airplane. The antenna is from Delta Pop Aviation. The coax cable is RG400 from B&C.

> 

> I have not checked the VSWR on the antenna. I see your book gives some instructions on how to do that.

> 

> The airplane is currently in my garage. Would that "focus" the RF energy more than being out in the open?

> 

> Thanks,

> Michael-

> 

> 

> On Jul 27, 2013, at 8:32 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

> 

>> 

>> 

>> At 06:59 PM 7/27/2013, you wrote:

>>> 

>>> 

>>> I'm trying to chase down a problem with my Radio (Garmin SL-40) Intercom (Flightcom 403) wiring. One of the strange behaviors that I don't understand is when I push the PTT to transmit on a common unicom frequency such as 122.7, the ammeter pegs at -40 amps. When I transmit on one of the maintenance frequencies such as 135.85, it only deflects negative 1-2 amps. But the radio is transmitting, I can hear on my handheld.

>>> 

>>> My ammeter is a shunt type ammeter and seems to work correctly in indicating positive (discharge)  loads for other equipment. What would make it indicate in the negative directions. This is using just the battery. i.e. engine not running.

>>> 

>>> The situation is that I'm trying to debug my initial wiring, so the setup has never worked.

>> 

>>  You didn't say but I'm betting your ammeter is

>>  the one Van's sells . . . minus 40 - zero - plus

>>  40?

>> 

>>  I have one of those things laying around here somewhere.

>>  I think I reported to the List after I bought it that

>>  the instrument was very vulnerable to strong RF

>>  in the cockpit.

>> 

>>  What kind of airplane and where is your antenna

>>  located? Have you checked VSWR on the antenna

>>  over the vhf comm range?

>> 

>> 

>>  Bob . . .

>> 

>> 

>> 

>> 

> 

> 

> 

> 

> 

>

enginerdy(at)gmail.com
Guest

Posted: Sun Jul 28, 2013 2:14 pm Post subject: COM radio/intercom wiring problem...

Are you using a shielded bundle to run the shunt sense wires? If so you could experiment with where you terminate the shield, whether that's at a ground near the shunt, or at a ground near the ammeter -- the idea would be to help get the RF energy shorted back to the source (the radio) without forcing it to go through the ammeter as it is now.



This particular model ammeter is passive, right? The shunt wires are the only two wires coming out of it?

On Jul 28, 2013, at 2:41 PM, Michael Burbidge wrote:



 	  Quote: 	
		   

 

 I hadn't noticed it, but the manifold pressure gauge, is also deflecting a good deal during radio transmission. I guess that's what I get for trying to be frugal with my instrumentation. I was alarmed by the ammeter deflection. But everything seems to be working otherwise, and there is no smoke or blown fuses, so I'm going to assume that this explains the ammeter deflection.

 

 Michael-

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jul 28, 2013 3:19 pm Post subject: COM radio/intercom wiring problem...

At 05:14 PM 7/28/2013, you wrote:

 	  Quote: 	
		  



Are you using a shielded bundle to run the shunt sense wires? If so 

you could experiment with where you terminate the shield, whether 

that's at a ground near the shunt, or at a ground near the ammeter 

-- the idea would be to help get the RF energy shorted back to the 

source (the radio) without forcing it to go through the ammeter as it is now.



This particular model ammeter is passive, right? The shunt wires are 

the only two wires coming out of it?


	


  Unfortunately, no. See:



http://tinyurl.com/mpx8hze



  This instrument is fitted with several 'radio

  receivers' in the form of op-amps.



  This design philosophy seems to be common to

  the whole product line. It's a fundamental

  design error which shielding of wires is

  unlikely to rectify.

   Bob . . .

enginerdy(at)gmail.com
Guest

Posted: Sun Jul 28, 2013 3:36 pm Post subject: COM radio/intercom wiring problem...

Zoiks.

Nice and cheap, but what are they gaining with all that circuitry? A stiffer needle? That can't be it... A lower-ohm shunt?

"..unlikely to rectify."

haha nice



On Jul 28, 2013, at 6:18 PM, Robert L. Nuckolls, III wrote:

[quote] 	  Quote: 	
		  

This particular model ammeter is passive, right? The shunt wires are the only two wires coming out of it?

	


 Unfortunately, no. See:



http://tinyurl.com/mpx8hze



 This instrument is fitted with several 'radio

 receivers' in the form of op-amps.



 This design philosophy seems to be common to

 the whole product line. It's a fundamental

 design error which shielding of wires is

 unlikely to rectify.

  Bob . . .          - The   -->             &n========================

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jul 28, 2013 4:52 pm Post subject: COM radio/intercom wiring problem...

At 06:35 PM 7/28/2013, you wrote:

 	  Quote: 	
		  Zoiks.



Nice and cheap, but what are they gaining with all that circuitry? A 

stiffer needle? That can't be it... A lower-ohm shunt?



"..unlikely to rectify."



haha nice


	


    Actually, it was probably done to achieve a design

    goal for an electronics assembly that would

    work across a lot of products . . . by changing

    scaling resistors and perhaps some jumpers you

    could built a host of instruments with great

    commonality of bill of materials.



    I too like to operate under that banner.

    If they're guilty of having fumbled the ball,

    it was lack of understanding the environment

    that their electro-whizzy was being asked to

    function. I'll bet their major market is

    automotive . . . vehicles without VHF

    transmitters.



   Bob . . .

mburbidg(at)gmail.com
Guest

Posted: Sun Jul 28, 2013 5:06 pm Post subject: COM radio/intercom wiring problem...

Wow I see from the link containing the pictures that the problems with this instrument are well known.

Since my airplane is VFR and I also have a voltmeter, I'm probably going to stick with my current setup at least until I'm flying. Perhaps I can find a drop-in replacement that works with the same shunt.

Michael-

On Jul 28, 2013, at 5:52 PM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:

 	  Quote: 	

 At 06:35 PM 7/28/2013, you wrote:

> Zoiks.

> 

> Nice and cheap, but what are they gaining with all that circuitry? A stiffer needle? That can't be it... A lower-ohm shunt?

> 

> "..unlikely to rectify."

> 

> haha nice

   Actually, it was probably done to achieve a design

   goal for an electronics assembly that would

   work across a lot of products . . . by changing

   scaling resistors and perhaps some jumpers you

   could built a host of instruments with great

   commonality of bill of materials.

   I too like to operate under that banner.

   If they're guilty of having fumbled the ball,

   it was lack of understanding the environment

   that their electro-whizzy was being asked to

   function. I'll bet their major market is

   automotive . . . vehicles without VHF

   transmitters.

  Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Aug 04, 2013 5:01 am Post subject: COM radio/intercom wiring problem...

At 11:17 PM 7/27/2013, you wrote:

 	  Quote: 	
		  



Yes, my ammeter is the Vans ammeter.



My airplane is an RV-9A. My COM antenna is mounted on the bottom of 

the airplane, approximately under where the left leg of the pilot is 

when sitting in the airplane. The antenna is from Delta Pop 

Aviation. The coax cable is RG400 from B&C.



I have not checked the VSWR on the antenna. I see your book gives 

some instructions on how to do that.



The airplane is currently in my garage. Would that "focus" the RF 

energy more than being out in the open?



Thanks,

Michael-


	


    Okay, for a metal airplane your narrative offers

    a stronger suggestion of coax shield unhooked at

    one end or the other causing a really 'hot' cockpit.

    This can be detected with an SWR check.



    Open shields can exhibit strong variations in

    observed effects depending on operating frequency.

    Alternatively, you just might have a particularly

    twitchy ammeter. The one I hooked up on the bench

    could be made to produce any reading from pegged

    minus to pegged plus or any place in between by

    waving my hand held around it. Effects on readings

    could be observed with the hand-held 3 feet away.



   Bob . . .

Display posts from previous:

	Matronics Email Lists Forum Index -> AeroElectric-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum