REFLECTOR: Trig TT-31 ADS-B transponder

[sbjknox at earthlink.net]

Well, as I suggested before, it appears to be that the transmitted rf from 
the transponder is getting (radiating) into circuits where it should not be. 
This can be caused by having the coax from your transponder too close to 
some other wiring.  There are various "qualities" of coax.  All coax will 
leak some rf but lesser quality coax can be unsuitable for rf transmission. 
Double-shielded (and more expensive) coax is probably best for transponder 
application.
With our plastic airplanes we will experience a higher lever of radiated rf 
inside the plane from comm and transponder transmitters than will those 
flying in spam-cans.
Or there may be a problem with the coax and/or the transponder antenna 
installatoin.  If the antenna (and the coax feeding it) has a problem then 
some of the rf that should be radiated will be reflected back to the 
transponder (excessive VSWR).  Also, the antenna needs to have a "ground 
plane" to operate correctly... ie., needs to be mounted on a metallic 
surface  (plate or screen) which is electrically bonded to the coax shield 
at the base of the antenna.  Mr Google can tell you all about it.
Even with your plane sitting on the ground your transponder will be 
interrogated by nearby ATC radar or by other aircraft.

Sid

----- Original Message ----- 
From: "John Dibble" <aminetech at bluefrog.com>

> Also, the noise goes away if I turn off the transponder.  In case I wasn't 
> clear this series of pops continues all the time the transponder is on.


> Looks like the noise is not random. It's 3 pops, each a second apart and 
> then a group of 3 which is what made it seem random.  I tried it inside 
> the hangar with the gps, encoder, intercom, radio, and noise cancelling 
> headset off.
>
> John
>
> On 12/30/2013 10:35 AM, sbjknox at earthlink.net wrote:
>> If the "...slight popping noise in my headset." is somewhat random in 
>> occurrence, it is probably the transponder's high-power rf response being 
>> picked-up by some portion of your audio system (com radio, intercom, 
>> headset...).  Watch the activity light on your transponder... if the 
>> radiated rf is causing the noise, it will be coincident with the light.
>> If the noise is not random but rather regular like once-per-second, then 
>> it is probably related to the serial data stream out of the GPS or some 
>> other serial data device that sends a data stream periodically.  If this, 
>> perhaps improper grounding of a shielded cable is the cause.
>>
>> $0.02
>> Sid Knox
>> Oklahoma
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