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Clicking Noise Coming From Transponder (Read 884 times)
Feb 5th, 2018 at 9:11am

HomeBuilt101   Offline
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I love flying!

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I have an annoying clicking sound that is coming from the transponder.  The clicking noise is a random series of clicks almost like somebody King the mic but a little bit quieter than that.

I have pulled all the circuit breakers in the airplane except for the circuit breakers that power the dynon screens and the dynon transponder.

When I pull the transponder circuit breaker the clicking noise stops. When I push in the circuit breaker for the transponder about 3 seconds later the clicking noise starts again so I have confirmed that it is indeed the transponder. . Any suggestions what this might be?
 
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Reply #1 - Feb 5th, 2018 at 12:17pm

Vern-X   Offline
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The Mode-S ES transponders transmit position reports every second or so.  What you are hearing is a small amount of RF interference due to this.  It is especially noticable inside a metal hangar, but not in flight because the transponder signal bounces around and is stronger as a result.

Some ANR headsets will pick this up even when unplugged from the aircraft and unpowered!  There are good technical reasons for this, but it's a bit like magic.

Vern
 
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Reply #2 - Feb 5th, 2018 at 2:16pm

HomeBuilt101   Offline
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Thanks Vern I appreciate your input. Regarding my other issue, called a Dynon  tech support.


He was stumped as well for a while and then after we did some troubleshooting he remembered a possible fix and then he was able to walk me through an internal squelch setting that is in one of the setup pages. I think it has solved the problem but I will wait on that definitive answer until I go and fly again but I think we got it!
 
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Reply #3 - Feb 5th, 2018 at 2:47pm

N214ST   Offline
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This may or may not be helpful, but Dynon has also recommended that the transponder tray itself be grounded if you have not already done so (see Figure 123 and bottom of page 11.9).  Grounding issues can cause all sorts of hard to troubleshoot issues, especially around radiated energy.  Also check your coax wire.  Sometimes you can have energy reflected back along the outside shield of a bad cable, and it will cause gremlin radiation patterns that may be picked up by your radio, or even as Vern has suggested, by an ANR headset.  There is also an outside chance it could be your antenna, so if you know someone with a VSWR meter, it would be helpful to test the VSWR of the antenna.  If you don't have anyone available, the VSWR meters are pretty cheap.  I have seen them on Amazon.com for less than $30.  Always a good item to have on hand.
 
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Reply #4 - Feb 5th, 2018 at 8:31pm

HomeBuilt101   Offline
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Thanks N214ST...good advice
 
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Reply #5 - Feb 6th, 2018 at 7:16am

airguy   Offline
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High quality coax is your friend here - it doesn't pay to save money on coax.
 
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Reply #6 - Feb 6th, 2018 at 7:47pm

jakej   Offline
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Australia

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In other words ..... RG400 coax or equivalent.  Anything else in an airframe that is not totally aluminium will mostly be a waste of time & money, especially ‘our’ time Wink
 
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Reply #7 - Feb 6th, 2018 at 8:16pm

HomeBuilt101   Offline
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Yes it has R400 cable
 
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Reply #8 - Feb 6th, 2018 at 11:20pm

jakej   Offline
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My comment was basically for the benefit of others here,  RG 58 (old standard) is soooo yesterday’s technology - now that the higher standard cabling is available & avionics are more ‘sensitive’ it’s the reason that you shouldn’t ( & not allowed, I think) use it in certified aircraft anymore. Smiley
 
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Reply #9 - Feb 7th, 2018 at 7:59am

Beersrus   Offline
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I recently installed a -261 XPNDR and have also noticed the clicking sounds.  In my case they seem to occur after powering up the intercom (obviously) but last only 30-60 seconds.  Then it is fine after that.  Particulars:
-261 unit mounted in Sportsman under rear seat
Using RG-400, runs about 5' to a Bob Archer antenna in tail
Same antenna used for 4 years with GTX327 - no clicking
-261 chassis is grounded with an extra wire

Certainly not a big issue, but interesting.

Russ
 
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