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Transponder constantly replies

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pete.howell(at)gecko-grou
Guest

Posted: Tue Sep 04, 2007 4:25 am Post subject: Transponder constantly replies

Hello,



I have an older transponder that seems to constantly generate replies

while airborne(solid light almost all the time).   ATC reports it is

working great, but I think it is causing issues with a traffic scope

I have installled.   Others report their transponder reacts the same

way, but more tell me they only get a reply on a sweep.   I am

wondering if a bad antenna cable or connector could cause this? 

Other thoughts welcome.

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sportav8r(at)gmail.com
Guest

Posted: Tue Sep 04, 2007 5:02 am Post subject: Transponder constantly replies

Mine (Garmin 320A) does that whenever the left Pmag is on ship's battery power but not when it's in self-powered mode.  Took me forever to figure out what the deal was.  I usually get normal function reports from ATC.  I'll be interested to see the consensus as to the likely cause of this behavior. 



-Bill B



On 9/4/07, Pete Howell <pete.howell(at)gecko-group.com (pete.howell(at)gecko-group.com)> wrote:[quote] --> AeroElectric-List message posted by: "Pete Howell" <pete.howell(at)gecko-group.com (pete.howell(at)gecko-group.com)>

Hello,



I have an older transponder that seems to constantly generate replies 

while airborne(solid light almost all the time).   ATC reports it is

working great, but I think it is causing issues with a traffic scope

I have installled.   Others report their transponder reacts the same

way, but more tell me they only get a reply on a sweep.   I am 

[b]

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nuckollsr(at)cox.net
Guest

Posted: Fri Sep 07, 2007 10:09 am Post subject: Transponder constantly replies

At 07:23 AM 9/4/2007 -0500, you wrote:



 	  Quote: 	
		  

<pete.howell(at)gecko-group.com>

Hello,



I have an older transponder that seems to constantly generate replies

while airborne(solid light almost all the time).   ATC reports it is

working great, but I think it is causing issues with a traffic scope

I have installled.   Others report their transponder reacts the same

way, but more tell me they only get a reply on a sweep.   I am

wondering if a bad antenna cable or connector could cause this?

Other thoughts welcome.


	


     I used to test transponders for reply codes by laying

     a noisy drill motor under the aircraft with a rubber

     band holding the trigger-switch ON. This would cause

     the transponder to dump a continuous stream of replies

     when there was no radar interrogation present.



     It MIGHT be that your transponder is seeing some

     kind of noise source that produces a similar response.



    Bob . . .

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

        ( "Physics is like sex: sure, it may   )

        ( give some practical results, but     )

        ( that's not why we do it."            )

        (                                      )

        (                 Richard P. Feynman   )

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

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Thermos

Joined: 08 Sep 2007
Posts: 3

Posted: Sat Sep 08, 2007 4:22 am Post subject: Re: Transponder constantly replies

Transponders reply to a pair of interrogation pulses with a specific spacing - the spacing determines reply type (Mode 3, Mode C, etc).  Anything that can generate that RF pulses with that spacing, like Bob's drill or a piece of computer equipment, could theoretically trigger a reply.  It seems unlikely that a loose connection could do that consistently enough to keep your reply light on, but stranger things have happened. 



It may be that your transponder is just receiving a lot of interrogations - ATC radars, military radars, TCAS - especially if you're flying in/around a busy terminal area.  If you can check with someone else flying close by at the same time and altitude, their transponder should be doing the same thing as yours if both boxes are working correctly.



Hope this helps...



Dave

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pete.howell(at)gecko-grou
Guest

Posted: Sun Sep 09, 2007 11:09 am Post subject: Transponder constantly replies

I found the cause for the runaway transponder.  This summer, I switched the

top plugs in my O-320 RV-9A with electronic ignition from std BR8ES auto

plugs to the iridium style auto plug.  I received an off list message

telling to look at the ignition system - sure enough the plug change matched

up with the tpx issue time frame.



Put in new plugs all around last night and things appear to be back to

normal.



Cheers,



Pete

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