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AT150 Interrogation Light

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Fox5flyer
Guest

Posted: Tue Jul 29, 2008 4:04 am Post subject: AT150 Interrogation Light

I have a Narco AT150 transponder in a Kitfox 5 with  the antenna on the belly with a 5.5" ground plate.  It seems to be working  fine according to ATC.  Good data and the mode C is accurate.   However, the interrogation light is on steady, rather than blinking as the radar  sweeps past it.  It used to be just fine, but at some point it began to act  differently where it would flicker, especially on the ground.  Now, if the  engine is off and I activate it, the interrogation light comes on for a few  seconds, then turns off.  I believe that's how it's supposed to act.   However, when flying, it seems to come on steady and stay that way with an  occasional flicker during flight.  As I said, ATC says it's working  fine.  

 Has anyone seen this?  Any idea what my  problem is?  Several times I've removed it, cleaned and lubed the contacts,  and replaced it with the same results.  Since it's working fine, I'm not to  worried about it, but I'd like to get this light working like it's supposed  to.

 Thanks for any help offered.

 Deke

  

   [quote][b]

mprather(at)spro.net
Guest

Posted: Tue Jul 29, 2008 7:27 am Post subject: AT150 Interrogation Light

Maybe you have something in the airplane generating noise which causes the

transponder to reply - even though it wasn't interrogated by an actual

radar signal.  How's the audio in your comm radio?  Any new noise?  Off

the top of my head, maybe you have a bad spark plug wire, or alternator

diode or something like that.  Does your engine have dual ignition

systems?  If yes, does the transponder behave the same way on each of them

separately?  Can you turn the alternator off and still run the txp from

battery (as a test)?  I doubt you have a DME in a Kitfox, but they operate

in the same band as the transponder so might be a source of interference.



As a long shot, possibly your cell phone is setting it off.  Did you get a

new phone?  Does it misbehave with the phone turned off?



I can't recall if the AT150 has a remote ident button, but maybe the wire

that connects that circuit isn't isolated properly.  I think those work by

grounding the wire.  Vibration might cause that wire to rub against

ground.  In reality, the pin in the shell connector for that function

probably doesn't even have a wire in it, so that's probably not the issue.



Maybe the reply discrimination circuit is messed up in your txp.  Possibly

a radio shop has a loaner unit you could swap into the tray.  Or maybe

they can test the unit for that functionality.

Regards,



Matt-



 	  Quote: 	
		   I have a Narco AT150 transponder in a Kitfox 5 with the antenna on the

 belly with a 5.5" ground plate.  It seems to be working fine according to

 ATC.  Good data and the mode C is accurate.  However, the interrogation

 light is on steady, rather than blinking as the radar sweeps past it.  It

 used to be just fine, but at some point it began to act differently where

 it would flicker, especially on the ground.  Now, if the engine is off and

 I activate it, the interrogation light comes on for a few seconds, then

 turns off.  I believe that's how it's supposed to act.  However, when

 flying, it seems to come on steady and stay that way with an occasional

 flicker during flight.  As I said, ATC says it's working fine.

 Has anyone seen this?  Any idea what my problem is?  Several times I've

 removed it, cleaned and lubed the contacts, and replaced it with the same

 results.  Since it's working fine, I'm not to worried about it, but I'd

 like to get this light working like it's supposed to.

 Thanks for any help offered.

 Deke

rjquillin

Joined: 13 May 2007
Posts: 123
Location: KSEE

Posted: Tue Jul 29, 2008 8:20 am Post subject: AT150 Interrogation Light

Matt, Deke,

I was thinking many of the same things, but given ATC was reporting 

his unit was 'normal', I discounted them, as I would have thought 

they would have complained of excessive replies or ident's making a 

mess of their sereens.  IIRC, the 150, unlike the 50, does have a 

remote ident pin.  I'll look in my SM tonight as see if there may be 

a some failure to the light circuit only, doesn't seem likely, but...

If the unit is in an area with many ADSB units and/or heavy radar 

coverage, it could actually be interrogated at some high rate and the 

reply light is working normally.  One would expect it to be a bit 

quieter on the ground, out of sight of multiple radar sites but 

perhaps still seeing ADSB inquires.  However, Deke reports a 

change.  Has anything else changed within the AC that may give a clue?

I agree, a bench check at a radio shop or exchange unit should be 

near the top of things to try.

Ron Q.

At 08:22 7/29/2008, you wrote:

 	  Quote: 	

Maybe you have something in the airplane generating noise which causes the

transponder to reply - even though it wasn't interrogated by an actual

radar signal.  How's the audio in your comm radio?  Any new noise?  Off

the top of my head, maybe you have a bad spark plug wire, or alternator

diode or something like that.  Does your engine have dual ignition

systems?  If yes, does the transponder behave the same way on each of them

separately?  Can you turn the alternator off and still run the txp from

battery (as a test)?  I doubt you have a DME in a Kitfox, but they operate

in the same band as the transponder so might be a source of interference.

As a long shot, possibly your cell phone is setting it off.  Did you get a

new phone?  Does it misbehave with the phone turned off?

I can't recall if the AT150 has a remote ident button, but maybe the wire

that connects that circuit isn't isolated properly.  I think those work by

grounding the wire.  Vibration might cause that wire to rub against

ground.  In reality, the pin in the shell connector for that function

probably doesn't even have a wire in it, so that's probably not the issue.

Maybe the reply discrimination circuit is messed up in your txp.  Possibly

a radio shop has a loaner unit you could swap into the tray.  Or maybe

they can test the unit for that functionality.

Regards,

Matt-

 > I have a Narco AT150 transponder in a Kitfox 5 with the antenna on the

 > belly with a 5.5" ground plate.  It seems to be working fine according to

 > ATC.  Good data and the mode C is accurate.  However, the interrogation

 > light is on steady, rather than blinking as the radar sweeps past it.  It

 > used to be just fine, but at some point it began to act differently where

 > it would flicker, especially on the ground.  Now, if the engine is off and

 > I activate it, the interrogation light comes on for a few seconds, then

 > turns off.  I believe that's how it's supposed to act.  However, when

 > flying, it seems to come on steady and stay that way with an occasional

 > flicker during flight.  As I said, ATC says it's working fine.

 > Has anyone seen this?  Any idea what my problem is?  Several times I've

 > removed it, cleaned and lubed the contacts, and replaced it with the same

 > results.  Since it's working fine, I'm not to worried about it, but I'd

 > like to get this light working like it's supposed to.

 > Thanks for any help offered.

 > Deke

 >

sportav8r(at)gmail.com
Guest

Posted: Tue Jul 29, 2008 1:04 pm Post subject: AT150 Interrogation Light

My Garmin xponder does that whenever both Pmags are powered up.  If I kill one side, it behaves normally again.  If I kill the other side, the problem remains.  ATC seems to see me okay most of the time while this is going on.  Strange, indeed.  Makes it hard to see true interrogation hits.

-Bill B

On Tue, Jul 29, 2008 at 12:13 PM, Ron Quillin <rjquillin(at)gmail.com (rjquillin(at)gmail.com)> wrote:

[quote] --> AeroElectric-List message posted by: Ron Quillin <rjquillin(at)gmail.com (rjquillin(at)gmail.com)>

 Matt, Deke,

 I was thinking many of the same things, but given ATC was reporting his unit was 'normal', I discounted them, as I would have thought they would have complained of excessive replies or ident's making a mess of their sereens.  IIRC, the 150, unlike the 50, does have a remote ident pin.  I'll look in my SM tonight as see if there may be a some failure to the light circuit only, doesn't seem likely, but...

 If the unit is in an area with many ADSB units and/or heavy radar coverage, it could actually be interrogated at some high rate and the reply light is working normally.  One would expect it to be a bit quieter on the ground, out of sight of multiple radar sites but perhaps still seeing ADSB inquires.  However, Deke reports a change.  Has anything else changed within the AC that may give a clue?

 I agree, a bench check at a radio shop or exchange unit should be near the top of things to try.

 Ron Q.

 At 08:22 7/29/2008, you wrote:

  	  Quote: 	
		   --> AeroElectric-List message posted by: "Matt Prather" <mprather(at)spro.net (mprather(at)spro.net)>

 Maybe you have something in the airplane generating noise which causes the

 transponder to reply - even though it wasn't interrogated by an actual

 radar signal.  How's the audio in your comm radio?  Any new noise?  Off

 the top of my head, maybe you have a bad spark plug wire, or alternator

 diode or something like that.  Does your engine have dual ignition

 systems?  If yes, does the transponder behave the same way on each of them

 separately?  Can you turn the alternator off and still run the txp from

 battery (as a test)?  I doubt you have a DME in a Kitfox, but they operate

 in the same band as the transponder so might be a source of interference.

 As a long shot, possibly your cell phone is setting it off.  Did you get a

 new phone?  Does it misbehave with the phone turned off?

 I can't recall if the AT150 has a remote ident button, but maybe the wire

 that connects that circuit isn't isolated properly.  I think those work by

 grounding the wire.  Vibration might cause that wire to rub against

 ground.  In reality, the pin in the shell connector for that function

 probably doesn't even have a wire in it, so that's probably not the issue.

 Maybe the reply discrimination circuit is messed up in your txp.  Possibly

 a radio shop has a loaner unit you could swap into the tray.  Or maybe

 they can test the unit for that functionality.

 Regards,

 Matt-

 > I have a Narco AT150 transponder in a Kitfox 5 with the antenna on the

 > belly with a 5.5" ground plate.  It seems to be working fine according to

 > ATC.  Good data and the mode C is accurate.  However, the interrogation

 > light is on steady, rather than blinking as the radar sweeps past it.  It

 > used to be just fine, but at some point it began to act differently where

 > it would flicker, especially on the ground.  Now, if the engine is off and

 > I activate it, the interrogation light comes on for a few seconds, then

 > turns off.  I believe that's how it's supposed to act.  However, when

 > flying, it seems to come on steady and stay that way with an occasional

 > flicker during flight.  As I said, ATC says it's working fine.

 > Has anyone seen this?  Any idea what my problem is?  Several times I've

 > removed it, cleaned and lubed the contacts, and replaced it with the same

 > results.  Since it's working fine, I'm not to worried about it, but I'd

 > like to get this light working like it's supposed to.

 > Thanks for any help offered.

 > Deke

 >

 [b]

Fox5flyer
Guest

Posted: Wed Jul 30, 2008 5:08 pm Post subject: Re: AT150 Interrogation Light

Thanks, Matt.  You've given me several things to try.  Yes, I do have a new cell phone and the first thing I'll try is to turn it off and see what happens.  I also have dual electronic ignition and I'll do some experimenting there too.  One thing I've noticed is that one of the ignitions has begun to make a noise in my headset.  Basically I can hear the trigger wheel going past the crank sensors, so I may have some wiring that is leaking through to the headset wiring and possibly to the transponder too.  Something to look at.  Other than that the ignitions seem to be operating fine, as is the alternator, however I have no way of turning it off.  The transponder acts normally when the engine isn't running.  I my area its very rural with no interrogation pulses until I get at least 2000agl, and even those are a long way off, so I'm not getting bombarded with pulses.

However, I do have some things to try.  Thanks.

Also, thanks to the others who offered help.

Deke





 	  mprather(at)spro.net wrote: 	
		  Maybe you have something in the airplane generating noise which causes the

transponder to reply - even though it wasn't interrogated by an actual

radar signal.  How's the audio in your comm radio?  Any new noise?  Off

the top of my head, maybe you have a bad spark plug wire, or alternator

diode or something like that.  Does your engine have dual ignition

systems?  If yes, does the transponder behave the same way on each of them

separately?  Can you turn the alternator off and still run the txp from

battery (as a test)?  I doubt you have a DME in a Kitfox, but they operate

in the same band as the transponder so might be a source of interference.



As a long shot, possibly your cell phone is setting it off.  Did you get a

new phone?  Does it misbehave with the phone turned off?



I can't recall if the AT150 has a remote ident button, but maybe the wire

that connects that circuit isn't isolated properly.  I think those work by

grounding the wire.  Vibration might cause that wire to rub against

ground.  In reality, the pin in the shell connector for that function

probably doesn't even have a wire in it, so that's probably not the issue.



Maybe the reply discrimination circuit is messed up in your txp.  Possibly

a radio shop has a loaner unit you could s

wap into the tray.  Or maybe

they can test the unit for that functionality.

Regards,



Matt-



 	  Quote: 	
		   I have a Narco AT150 transponder in a Kitfox 5 with the antenna on the

 belly with a 5.5" ground plate.  It seems to be working fine according to

 ATC.  Good data and the mode C is accurate.  However, the interrogation

 light is on steady, rather than blinking as the radar sweeps past it.  It

 used to be just fine, but at some point it began to act differently where

 it would flicker, especially on the ground.  Now, if the engine is off and

 I activate it, the interrogation light comes on for a few seconds, then

 turns off.  I believe that's how it's supposed to act.  However, when

 flying, it seems to come on steady and stay that way with an occasional

 flicker during flight.  As I said, ATC says it's working fine.

 Has anyone seen this?  Any idea what my problem is?  Several times I've

 removed it, cleaned and lubed the contacts, and replaced it with the same

 results.  Since it's working fine, I'm not to worried about it, but I'd

 like to get this light working like it's supposed to.

 Thanks for any help offered.

 Deke

nuckolls.bob(at)cox.net
Guest

Posted: Wed Jul 30, 2008 6:17 pm Post subject: AT150 Interrogation Light

At 06:08 PM 7/30/2008 -0700, you wrote:

 	  Quote: 	
		  



Thanks, Matt.  You've given me several things to try.  Yes, I do have a 

new cell phone and the first thing I'll try is to turn it off and see what 

happens.  I also have dual electronic ignition and I'll do some 

experimenting there too.  One thing I've noticed is that one of the 

ignitions has begun to make a noise in my headset.  Basically I can hear 

the trigger wheel going past the crank sensors, so I may have some wiring 

that is leaking through to the headset wiring and possibly to the 

transponder too.  Something to look at.  Other than that the ignitions 

seem to be operating fine, as is the alternator, however I have no way of 

turning it off.  The transponder acts normally when the engine isn't 

running.  I my area its very rural with no interrogation pulses until I 

get at least 2000agl, and even those are a long way off, so I'm not 

getting bombarded with pulses.

However, I do have some things to try.  Thanks.

Also, thanks to the others who offered help.


	


   Got in on this thread late but as others have noted,

   the transponder receiver is rather 'twitchy' with

   respect mistaking incoming noises as a bona fide

   "paint" from a ground based radar.



   A technician I used to work with had some rubber

   bands permanently installed over the hand grip

   on his line operated electric drill. I asked what

   they were for and he was happy to demonstrate. Use

   the rubber bands to hold the trigger made and then

   lay the drill on the floor right under the transponder

   antenna. From outside the cockpit you could see the

   reply light going nutso. He had one of those altitude

   and squawk code receiver/readouts that could then

   be used to see if the altimeter encoder was reading

   the same as the pitot-static test set altitude.



   The drill motor and the el-cheeso readout accessory

   took the place of some rather expensive test equipment

   for doing pitot static tests.



   Try pulling all the breakers/fuses except transponder.

   See if effects go away. Reinstall feeder protection

   one device at a time to see if you can identify the

   one that's upsetting the transponder. But all who

   have responded to this thread have identified possibilities

   for pesky little noises that might be causing the

   problem. It doesn't take much.



   Bob . . .

Fox5flyer
Guest

Posted: Thu Jul 31, 2008 8:32 am Post subject: Re: AT150 Interrogation Light

Thanks for your reply, Bob.  I appreciate all input.  Well, I flew this morning for about an hour and the first thing I checked was that my cell phone was turned off.  No change.  At cruise the light was on steady.  Next, I switched off my left ignition which did two things.  It stopped the noise in my headset and the interrogation light on the transponder went out and started blinking normally!  I'm getting close.  So, now I can tear into the wiring and see where my left ignition wiring is in a common bundle with my headset receive and also the transponder.  What would you suggest here?  Obviously I need to either separate some wiring or do some shielding, but I'm not sure which way I should go.  If you were to home in on a specific wire, which would it be?  My engine is the NSI EA81 with stock Electromotive ignition modules.  I personally don't think anything is wrong with the ignitions.  I believe I just have an ignition wire somewhere causing interference.  I'll dig my schematics out to see if I can experience an epiphany. 

Thanks again,

Deke

NE Michigan



 	  nuckolls.bob(at)cox.net wrote: 	
		  At 06:08 PM 7/30/2008 -0700, you wrote:

 	  Quote: 	
		  



Thanks, Matt.  You've given me several things to try.  Yes, I do have a 

new cell phone and the first thing I'll try is to turn it off and see what 

happens.  I also have dual electronic ignition and I'll do some 

experimenting there too.  One thing I've noticed is that one of the 

ignitions has begun to make a noise in my headset.  Basically I can hear 

the trigger wheel going past the crank sensors, so I may have some wiring 

that is leaking through to the headset wiring and possibly to the 

transponder too.  Something to look at.  Other than that the ignitions 

seem to be operating fine, as is the alternator, however I have no way of 

turning it off.  The transponder acts normally when the engine isn't 

running.  I my area its very rural with no interrogation pulses until I 

get at least 2000agl, and even those are a long way off, so I'm not 

getting bombarded with pulses.

However, I do have some things to try.  Thanks.

Also, thanks to the others who offered help.



	


   Got in on this thread late but as others have noted,

   the transponder receiver is rather 'twitchy' with

   respect mistaking incoming noises as a bona fide

   "paint" from a ground based radar.



   A technician I used to work with had some rubber

   bands permanently installed over the hand grip

   on his line operated electric drill. I asked what

   they were for and he was happy to demonstrate. Use

   the rubber bands to hold the trigger made and then

   lay the drill on the floor right under the transponder

   antenna. From outside the cockpit you could see the

   reply light going nutso. He had one of those altitude

   and squawk code receiver/readouts that could then

   be used to see if the altimeter encoder was reading

   the same as the pitot-static test set altitude.



   The drill motor and the el-cheeso readout accessory

   took the place of some rather expensive test equipment

   for doing pitot static tests.



   Try pulling all the breakers/fuses except transponder.

   See if effects go away. Reinstall feeder protection

   one device at a time to see if you can identify the

   one that's upsetting the transponder. But all who

   have responded to this thread have identified possibilities

   for pesky little noises that might be causing the

   problem. It doesn't take much.



   Bob . . .

etienne.phillips(at)gmail
Guest

Posted: Thu Jul 31, 2008 9:00 am Post subject: AT150 Interrogation Light

Could it be a spark-plug lead connected to the left ignition circuit that has a problem with it's shielding?



Etienne



2008/7/31 Fox5flyer <fox5flyer(at)idealwifi.net (fox5flyer(at)idealwifi.net)>

 [quote]--> AeroElectric-List message posted by: "Fox5flyer" <fox5flyer(at)idealwifi.net (fox5flyer(at)idealwifi.net)>

  

 Thanks for your reply, Bob.  I appreciate all input.  Well, I flew this morning for about an hour and the first thing I checked was that my cell phone was turned off.  No change.  At cruise the light was on steady.  Next, I switched off my left ignition which did two things.  It stopped the noise in my headset and the interrogation light on the transponder went out and started blinking normally!  I'm getting close.  So, now I can tear into the wiring and see where my left ignition wiring is in a common bundle with my headset receive and also the transponder.  What would you suggest here?  Obviously I need to either separate some wiring or do some shielding, but I'm not sure which way I should go.  If you were to home in on a specific wire, which would it be?  My engine is the NSI EA81 with stock Electromotive ignition modules.  I personally don't think anything is wrong with the ignitions.  I believe I just have an ignition wire somewhere causing interference.  I'll dig my schematics out to see if I can experience an epiphany.

  Thanks again,

 Deke

 NE Michigan

 

 

[b]

mprather(at)spro.net
Guest

Posted: Thu Jul 31, 2008 9:39 am Post subject: AT150 Interrogation Light

Deke,



Sounds like you're making progress..  Does the engine have two plugs per

cylinder?  If so, the problem could be as simple a faulty high tension

lead - or even a bad plug.



Along these lines, my guess would be that the source of noise is in the

high-energy portion of the system - as that seems most likely to radiate

offensive noise.  That's why I'd guess the noise is from a high tension

lead.



If not dual plugs, does your system use a coil switcher?  If so, maybe the

noise is in that portion of the circuit.



Good luck!

Matt-



 	  Quote: 	
		   

 <fox5flyer(at)idealwifi.net>



 Thanks for your reply, Bob.  I appreciate all input.  Well, I flew this

 morning for about an hour and the first thing I checked was that my cell

 phone was turned off.  No change.  At cruise the light was on steady.

 Next, I switched off my left ignition which did two things.  It stopped

 the noise in my headset and the interrogation light on the transponder

 went out and started blinking normally!  I'm getting close.  So, now I can

 tear into the wiring and see where my left ignition wiring is in a common

 bundle with my headset receive and also the transponder.  What would you

 suggest here?  Obviously I need to either separate some wiring or do some

 shielding, but I'm not sure which way I should go.  If you were to home in

 on a specific wire, which would it be?  My engine is the NSI EA81 with

 stock Electromotive ignition modules.  I personally don't think anything

 is wrong with the ignitions.  I believe I just have an ignition wire

 somewhere causing interference.  I'll dig my s!

  chematics out to see if I can experience an epiphany.

 Thanks again,

 Deke

 NE Michigan

Fox5flyer
Guest

Posted: Fri Aug 01, 2008 4:35 am Post subject: Re: AT150 Interrogation Light

Thanks, Matt.  First, the engine uses one plug per cylinder.  The two ignitions come together in coil joiners (isolation modules).  I'd considered the possibility of a bad high tension lead, but sort of discounted that because the engine runs great from either ignition with no drop at all with mag checks.  Then again, that's just my logic talking and it doesn't mean that it's not a high tension lead.  I've changed plugs with the same result.  If I could figure out what "might" be causing it, I could probably do a little wire sorting and find the culprit, but I'm just not knowledgeable enough to get a clear picture in my mind what is happening.  Obviously, it's emanating from the left ignition circuit because when I turn off power to it, the noise in my headset stops and the interrogation light on the transponder goes out.  I've already checked all of the high tension leads with an ohm meter and none are significantly different which leads me to believe the problem lies in the "placement" of my wiring bundles somewhere.  Am I making sense?

Thanks again,

Deke

 	  mprather(at)spro.net wrote: 	
		  Deke,



Sounds like you're making progress..  Does the engine have two plugs per

cylinder?  If so, the problem could be as simple a faulty high tension

lead - or even a bad plug.



Along these lines, my guess would be that the source of noise is in the

high-energy portion of the system - as that seems most likely to radiate

offensive noise.  That's why I'd guess the noise is from a high tension

lead.



If not dual plugs, does your system use a coil switcher?  If so, maybe the

noise is in that portion of the circuit.



Good luck!

Matt-



 	  Quote: 	
		   

 <fox5flyer>



 Thanks for your reply, Bob.  I appreciate all input.  Well, I flew this

 morning for about an hour and the first thing I checked was that my cell

 phone was turned off.  No change.  At cruise the light was on steady.

 Next, I switched off my left ignition which did two things.  It stopped

 the noise in my headset and the interrogation light on the transponder

 went out and started blinking normally!  I'm getting close.  So, now I can

 tear into the wiring and see where my left ignition wiring is in a common

 bundle with my headset receive and also the transponder.  What would you

 suggest here?  Obviously I need to either separate some wiring or do some

 shielding, but I'm not sure which way I should go.  If you were to home in

 on a specific wire, which would it be?  My engine is the NSI EA81 with

 stock Electromotive ignition modules.  I personally don't think anything

 is wrong with the ignitions.  I believe I just have an ignition wire

 somewhere causing interference.  I'll dig my s!

  chematics out to see if I can experience an epiphany.

 Thanks again,

 Deke

 NE Michigan

nuckolls.bob(at)cox.net
Guest

Posted: Fri Aug 01, 2008 5:05 am Post subject: AT150 Interrogation Light

At 05:36 AM 8/1/2008 -0700, you wrote:

 	  Quote: 	
		  



Thanks, Matt.  First, the engine uses one plug per cylinder.  The two 

ignitions come together in coil joiners (isolation modules).  I'd 

considered the possibility of a bad high tension lead, but sort of 

discounted that because the engine runs great from either ignition with no 

drop at all with mag checks.  Then again, that's just my logic talking and 

it doesn't mean that it's not a high tension lead.  I've changed plugs 

with the same result.  If I could figure out what "might" be causing it, I 

could probably do a little wire sorting and find the culprit, but I'm just 

not knowledgeable enough to get a clear picture in my mind what is 

happening.  Obviously, it's emanating from the left ignition circuit 

because when I turn off power to it, the noise in my headset stops and the 

interrogation light on the transponder goes out.  I've already checked all 

of the high tension leads with an ohm meter and none are significantly 

different which leads me to believe the problem lies in th!

  e "placement" of my wiring bundles somewhere.  Am I making sense?


	


    On the TC side of aviation's house, all appliances considered

    for use on airplanes is evaluated for its stand-alone

    characteristics with respect to noise emissions, noise

    vulnerabilities, temperature limits, etc. The goal is

    to offer smooth integration of that device into an

    airplane where the installer does not need to accommodate

    a shortfall in performance.



    I presume that you have two identical ignition systems

    of which only one causes noise. I'm presuming further

    that few (if any) other builders have experienced the

    noise issues with these systems. This leads me to

    suggest that there is something "different" about the

    two systems installed on your airplane. It might be

    fixed by a wire installation revision . . . but if so,

    then perhaps theses systems have not been sufficiently

    refined sufficiently for smooth integration into aircraft.



    I mention all this because it offers a mode of investigation

    that looks for differences between the two systems. One

    generates an unacceptable level of noise while the other

    does not. How are wires routed differently between the two?

    You might try swapping components between the two systems

    to see if the problem follows the swap. You can use the

    12 lantern battery experiment to power each system up

    independently from ship's power . . . although this is

    a very long shot for a noise that the transponder sees.



    The transponder has already been qualified to tolerate

    a lot of conducted noise into ship's wiring . . . the

    energy that upsets it now is probably coming through

    the antenna. So, try disconnecting the transponder

    antenna for a short test to see if it stops triggering

    on the noise.



    This is a game of clue. You've identified the source

    of noise and victim to that noise. Now you need to

    ferret out the propagation mode. Once that's identified,

    the fix will be easy.



    Bob . . .

Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Fri Aug 01, 2008 5:59 am Post subject: AT150 Interrogation Light

One cheap "tester" to find the source of the noise, is an old Walkman or 

equivalent radio(yeah, those things about 2 generations older than the 

Ipod), tuned away from any station, on the AM band, preferably near the 

top...1650 or thereabouts.  Then just move it about taking all necessary 

precautions with regard to the prop slice/dicer up front. Wherever the 

noise peaks, is the location of the offender. I've found bad voltage 

regulators that way, among other things. Just a resistance reading 

doesn't prove a high tension lead isn't leaking noise, only proves 

continuity.



Fox5flyer wrote:

 	  Quote: 	
		   



 Thanks, Matt.  First, the engine uses one plug per cylinder.  The two ignitions come together in coil joiners (isolation modules).  I'd considered the possibility of a bad high tension lead, but sort of discounted that because the engine runs great from either ignition with no drop at all with mag checks.  Then again, that's just my logic talking and it doesn't mean that it's not a high tension lead.  I've changed plugs with the same result.  If I could figure out what "might" be causing it, I could probably do a little wire sorting and find the culprit, but I'm just not knowledgeable enough to get a clear picture in my mind what is happening.  Obviously, it's emanating from the left ignition circuit because when I turn off power to it, the noise in my headset stops and the interrogation light on the transponder goes out.  I've already checked all of the high tension leads with an ohm meter and none are significantly different which leads me to believe the problem lies in th!

  e "placement" of my wiring bundles somewhere.  Am I making sense?

 Thanks again,

 Deke

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

nuckolls.bob(at)cox.net
Guest

Posted: Fri Aug 01, 2008 6:46 am Post subject: AT150 Interrogation Light

At 06:55 AM 8/1/2008 -0700, you wrote:

 	  Quote: 	
		  



One cheap "tester" to find the source of the noise, is an old Walkman or 

equivalent radio(yeah, those things about 2 generations older than the 

Ipod), tuned away from any station, on the AM band, preferably near the 

top...1650 or thereabouts.  Then just move it about taking all necessary 

precautions with regard to the prop slice/dicer up front. Wherever the 

noise peaks, is the location of the offender. I've found bad voltage 

regulators that way, among other things. Just a resistance reading doesn't 

prove a high tension lead isn't leaking noise, only proves continuity.


	


   Good point! I've still got some pocket transistor

   radios around that have been used for that purpose

   years ago. In my case, I was tracking down arcing

   insulators on power poles. The directional qualities

   of their "loopstick" antennas can be exploited to

   deduce direction of a received signal (as described

   in the 'Connection's chapter on antennas).



   I've not had occasion to use one of these radios

   in many years. I heard of a more modern utilization

   in a class on RFI/EMC issues about 15 years ago. The

   speaker told how he boxed a pocket radio up in an

   RF tight, aluminum enclosure. He brought a coax

   connector through the box and tied it to a "primary

   of a transformer" wound around the radio. I think

   it was 5 turns of 22awg wire. He also brought out

   the headphone circuit through RFI filters.



   The radio was turned ON, tuned to the high end

   of the band, volume up to max and the box closed.

   A short piece of coax could be fitted at the end

   with either magnetic or electric field probes



http://aeroelectric.com/Pictures/Tools/RF_Antenna_Test_Tools/Sniffer_Probes.jpg



   I built these probes for use on a very broadband

   spectrum analyzer. Another name for a fancy

   receiver.



   This poor man's electronic "stethoscope" was useful

   for "sniffing" about the airplane for the purpose

   of pinpointing the exit location for a radiated

   noise source. This also assumes that the noise

   source is also broad band with components in the

   audible range. In other words, a relatively clean,

   RF energy or energy at very high frequencies would

   not produce a signal that one would expect to hear

   with this tool.



   In the case before us, the repetition rate for

   ignition system currents are very much in the audio

   range and have a base-band component that is at

   or below the broadcast band detection range of

   the pocket radio.



   This system would not be useful for finding

   conducted noise sources where the offending signal

   stays pretty much in the wiring. Once it's absolutely

   confirmed that the transponder's antagonist is

   radiated (coming in through the antenna) then

   perhaps Kelly's suggestion offers a useful tool for

   further investigation.



   Bob . . .

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