Mode S Tranponder noise in headsets

[Mooney_Allegro]

For those of you using ANR headsets,  such as the Bose X or Lightspeed Zulu, AND that either have or are upgrading to the Mode S tranponder, you will probably hear sparking noise or crackling in your headset.  The noise is not heard from the less powerful Mode C transponder which I had before. Since the Mode S transmits more info and is more powerful, the ANR headsets pickup this noise and it's very disturbing to hear on long flights, even above the XM radio.  My avionics shop has been working on the problem on and off for months, and after upgrading shielding, moving wires around, pulling out the avionics rack, checking grounds, pulling the interior out, checking the antenna, calling the Garmin techs about a dozen times, the only thing that solved this problem was moving the Mode S antenna from under the cockpit belly to the rear belly of the plane.  Garmin suggested doing this as a last resort.  At the avionics shop, we even climbed into another Mooney that was equipped with the Mode S and we heard the same sparking noises using the Bose and Lightspeed headset.  You can hear the sparking noise with the Bose or Lightspeed plugged into the panel, or not, even if you are outside of the aircraft by the wingtip, you will still hear the sparking noises when the Mode S was either in Ground mode, On, Alt.  You don't hear it when in Standby or Off. 

So my point here is to move your transponder antenna to as far aft on the belly as possible if you have a Mode S and use an ANR headset and hear the annoying noises in your headset.  I spent over $1200 just on this issue, mostly on labor, only $150 for the new antenna.  They just left the old mode S antenna in place to save in labor costs of removing it and patching the hole. 

[Magnum]

I have a Trig TT31 Mode S transponder and no problems with my Bose headsets. The Trig has 240 Watts output and the antenna is located a few inches behind the exhaust.

[MikeinFL]

Allegro,

 

I upgraded my 327 to a 330 a few months ago and now hear the same "sparking" noise on my Zulu's!!!   My transponder antenna is located behind the exhaust pipe.   Once it starts getting on my nerves I now know what to do.

 

I owe you a beer!

 

Mike

[The-sky-captain]

I do not have the transponder problem but I do always hear my strobes pulsing in my headphones when I  taxi or am sitting still. Is this pretty common?

[aschardt]

I get the strobe pulse in my Bose X's too.  I have a PS Engineering 1000II intercom.  I think it's a grounding issue but it's not all that loud for me so I haven't pursued it.

 -Aaron

[N6843N]

*not correct poster*

[piperpainter]

My strobes don't cause that but my beacon does. At least I don't notice the strobes cause the beacon is so noticable. I have gotten used to it though and now only notice it when its not there or when friends ask what the heck that noise is!

 

sorry N6843N it posted under your name first!

 

[The-sky-captain]

Bryan- The shiny spinner looks good in the new pics you posted.

[N6843N]

Not a problem. Wow a C-17 loadmaster ehh. Somewhere around here I have a souvenir back scratcher from the day they rolled the first one out in Long Beach. I grew up around the USAF, my Dad's last A/C was the C-133 before that was 124's 47K flight hours those old birds were a slow ride across the Pacific. He had quite a soft spot for Douglas built aircraft.

[Piloto]

It is not uncommon for ANR headsets to be RFI (Radio Frequency Interference) sensitive. The problem is common on HF equipped small planes and helicopters. (100 to 400 watts). It is also annoying for helicopter power line inspection crew when they get close to HV lines. Looking at some ANR designs I can see that there is no provision to reduce RFI susceptibility. On some ANRs the cords are not even shielded and none have shielded electronics. I think RFI susceptibility should be part of the TSO requirements.

José