MGL Avionics User Forum

I am experiencing feedback when a second Flycom helmet is connected to my Trike. The only way to reduce it is to set my pilot mic gain to -3 db or more (-5 db). Works great without the second helmet.Intercom volume must be less than 3 as well.
Any ideas?
Antenna looks good and grounds look connected.

Thanks in advance.

RF is getting into your second audio lines at a level sufficient to start the oscillation.
In this case the easiest method to fix would be to attenuate the RF on on your audio (microphone) lead using a ferrite.

Could it be wind noise picked up by the second mic when it's connected? I had this problem in an open ultralight Drifter which was solved with a larger muff on the mic.
Cheers
Mike

I'm using a V16 radio in my trike also with FlyCom helmets. I'm also getting feedback (a somewhat high pitch sound that sounds like it's in a tunnel). This sound is happening while I speak and is heard by the other side. I have the mic gain set to -12 db. I believe I'm getting this both with one or two helmets. The way the Flycom system works, there's only one mic connection. So far I haven't been able to make it go away and I've installed sever ferrite chokes (can do more). Is there something else that can be done? Thanks!
David

Unusual to have a V16 on a trike...

It's quite a powerful radio so it gets more tricky to radiate the RF power - anything not radiated goes straight back to the radio and with that any attached wiring where it can cause havoc including RF feedback.

It's important to figure out where the RF is getting into the system - either via reflected RF or via the audio leads (other leads can also do this but tend to have lesser effect). If it is reflected RF you need to figure out a way to improve the ability of your antenna installation to get rid of the energy to where you want it (in the air) - while at the same time ensuring that none of your other wiring is close enough or of suitably tuned length to act as receiving antenna for that power.
If it is getting into your audio leads a small audio transformer can do wonders - see the example wiring that allows DC for the mic amp to pass in the A16 manual. Ferrites are also effective but must be installed at strategic locations - they can be used to worsen the problem if you use them to accidentally create tuned lengths of wires.

The V16 has a TXDelay setting that sometimes helps (depending on circumstances). This delays the outgoing audio for a short time interval (I think it is around 50 millisecond or so). This helps to break the feedback loop or at least helps to prevent getting it started (once it starts the delay makes no difference as it still gets a feedback signal that is perfectly in phase - just delayed).

The V6 wasn't available at the time, so I ended up with the V16. SVWR is 1.0 as measured on the radio, so the ground plane appears to be good and the reflected power should be minimal. Used RG-400 for the coax to the radio. I'm running the radio at 5W as well which should reduce the amount of feedback. I can try the TX delay. Receive has no issues with noise, only transmit. I tried to keep the wiring separated as much as possible but space is limited. Before I sent off the radio for a repair (capacitor failed), I did not appear to get this issue, so I thought the wiring was good. In fact, after the repair was made I stopped hearing my strobes in the intercom. I can try the delay. Any suggestions on how to find the strategic points to put ferrite chokes? Also, after the repair, the firmware was updated and a new menu item showed up that is not documented (mic filter I believe, shows narrow, normal, and medium). What does this do? Thank you for the help.

The mic filter is a band filter that cuts high and low frequencies. In previous firmware releases it was fixed - now you can choose the width of it. It helps to cut out unwanted noise in some cases.

I had this exact same problem with feedback and very garbled noisy transmit. Worked from passenger side. Was ready to replace the radio. Checked factory 2 place harness and the PTT ground was on the headphone ground pin(21). Moved it to the correct pin (11) and problem solved