I have recently installed a TY91 in my homebuilt project but have an annoying background noise issue. Trig have been very helpful and initially sent me a service exchange unit, which made no difference, and more recently have had my whole setup in their workshop.
I have refitted the unit, complete with new harness, but the noise is still there. As they say, once the engine is running I might not be able to hear it (although I disagree) but what if I were flying a glider? Has anyone else had this problem?
Where is the noise coming from? Is it coming from the unit itself, or something you can hear in the headset(s)? Is it constant, or does it correlate with being interrogated by a radar?
It is generated by the unit itself, and is a constant low frequency buzzing or hissing, like white noise, overlaid by a clicking sound, with the clicks about 2 per second. My project is unfinished and currently still in the workshop. I initially thought the noise might come from the fluorescent lights, but no.
Trig have intimated that it emanates from the link between the radio unit and the separate tuning head (in other words, they admit it’s there), but I can’t understand why it’s so prevalent. I listened to their demo unit at Aeroexpo and it was totally silent.
That’s completely weird. Do you mean you have the transponder just sitting there, wired up to power and an antenna and maybe some other bit of kit, and there is noise emanating from the transponder box itself which you can hear with your bare ears?
It sounds like a switch mode power supply whose ferrite (transformer) components have not been bonded together with varnish. I used to design power supplies and we used to vacuum varnish the ferrite transformers. However, metal (laminated) transformer cores can be just as noisy.
This will void the warranty but I would open it up and see what is actually making the noise. In electronics, there isn’t much that can make noise. Then get some 2-pack lacquer (polyurethane for example; used by model aircraft builders) and put a lot of it into the offending transformer 
My experience is that typical EU 8.33Khz radios are more sensitive to EMC than their 25Khz counterparts. I saw that after installing a trig and a F.U.N.K.E.
If you have a tick tick 2 times per second, this could be due to the fact that the radio antenna is too close to the transponder antenna. Or a bad ground of any antenna.
Yikes! I’m not about to go monstering the unit and filling it with goo but I agree, it’s bizarre. You can connect it up on the bench, plug in a headset, turn it on and….hiss, click click click. It’s really irritating. It’s a comm by the way, not a transponder. No external influences at all. The sound level doesn’t alter with the volume control, which is why Trig suggested turning down the headset volume and turning up the radio. But even doing that, at an acceptable level of reception volume, the background noise is still plainly and annoyingly audible.
I’ve never experienced such a thing throughout my flying (including airline) career. I find the whole thing baffling. Why would Trig allow it?
You will probably find it is just one really obvious component that’s doing it. It’s called magnetostriction.
Have done quite a lot of Trig TY-91, and never had that issue. I am quite sure they would do all that is possible to help you. They have the BEST support arround, and it should be able to work just fine. I would not open the unit yourself.
Have you been at Trig while they performed the test, or did you have the units returned? What kind of power supply do you use at your aircraft and on the bench? When on the aircraft, did you have an external power / battery charger installed?
You will probably find it is just one really obvious component that’s doing it. It’s called magnetostriction.
Correct me if I’m wrong – but he’s hearing it through the headset, not sound emanating through the box and travelling through the air?
I did ask “which you can hear with your bare ears?” but it may have been misinterpreted.
If it is in the headset then forget everything I have written; it could be anything…
