I finally got myself a basic ANR headset (hmec 250). These are great as yesterday after a 2 hours flight I didn’t have a headache :)
However, since the engine noise is quieter I start hearing all the background electronic noise louder and it’s really annoying.
I switch on the beacon… a low wailing noise is heard
I switch on the transponder… a periodic cracking starts
I switch on the strobes… a charge/discharge noise is audible
These are not really loud noises… but when heard together they make quite an annoying racket…
I’ve noticed this in virtually every aircraft at our club (some less than others).
Is this something really common? Does it happen with newer aircraft/avionics?
Very common in old aircraft. In my experience, especially so in Pipers. Is it a Piper?
Badly done wiring… unshielded cables, shielded cables with the shield not grounded, etc.
I can hear cellphone/satphone activity loudly in my Bose headsets (can usually tell if somebody sends me an SMS 
) but that’s about it for noises during flight. On the ground, there is probably more.
Radar can also be heard loudly, with a loud ping as the antenna rotates.
Yesterday it was a 172… but it also happens on the PA28.
Yes they’re all quite old.
So I guess if I want quiet, it’s not enough to spend £400 on a headset… I need to buy myself a new aircraft
Badly done wiring… unshielded cables, shielded cables with the shield not grounded, etc.
… shielded cables with shield grounded both sides, grounds all over the place instead of (as close as possible to) a single star …
It must be aircraft cabling specific as I have the Sennheiser noice cancelling headsets, and while I dont think they are particuarly great, in my 1979 PA28 I pick up no interference from any device at all. The only exception is my flying partners Blackberry which I insist he switches off.
You don’t need a lot of wiring to be done incorrectly to be hearing this stuff in the headsets. It takes RF pickup on just 1 or 2 wires entering the intercom.
I would start by un-selecting all switched sources and see if any of it goes away. If not, it is probably coming in via one of the unswitched inputs.
That’s all assuming there is a proper intercom (“audio panel”). If there isn’t, all bets are off because planes that don’t have an intercom tend to be a big wiring mess.
The problem is the wiring. Microphone wiring is most sensitive to this (very low level signal). What kind of equipment do you have? Some stand-alone intercoms for example are really poor quality with respect to interference. Such as the Sigtronics ones with the completely plastic housing and unshielded wires all over the place.
The same is true for older audio panels etc.
Even most manufacturers get it wrong with their grounding procedures. Grounding shield should be as short as possible. A 10 cm pigtail from shield to ground ruines the complete effect of the shielding. These wires should be kept really short. The RF signal gets demodulated inside the electronics, so it is important to filter this.
Newer aircraft have better wiring on both audio and RF. An RG-58 with a poor quality shield (open) can leak quite some RF. This can be a problem where the distance between wiring is small.
It is always good practice to keep coax cables, and high current loads seperate from data and audio wiring.
We had similar problems. Once the new Bose headsets went in I started to hear all kind of interference. Those are the lessons I learned.
What you hear depends a lot on the pilot. I hear all kind of interference while my copilot will not hear much at all. Keep that in mind if somebody tells some aircraft is better than another free…
If you can not change the whole aircraft wiring here are some options:
- You can fit some resistor in the audio line to the headset and then turn up the volume on the audiopanel. This will reduce the volume of the interference as its level will decrease compared to the signal level.
- If you want to go any further you can buy some audio equipment and build a gate/threshold circuit you plug between the headset and the aircraft. The effect is if the audio signal drops below a certain level the line will be shut off completely eliminating all background noise.
Certain types of “interference” can be defeated with audio line transformers, these are on sale for car audio systems. Better to avoid the need, though, by wiring correctly. And if one decides to try the transformer way, some luck and some insight and a fair deal of trial and error will be required.
