Intercom squelch.

[Bill RV4]

I have an RV4 with all Dynon avionics. All works well..... except with a passenger in the back, in flight or high engine power (run ups/ Take off) I can not "squelch out" the intercom. It is constant noise. With just me in, everything is fine. Is there some extra form of adjustment somewhere? Other than:-
"To adjust squelch with the engine running: 1. While no one is talking, turn the squelch knob until you hear background noise in your headset. 2. Adjust the squelch until you no longer hear background noise. 3. With the microphone close to your mouth, talk to confirm that normal speech levels activate the microphone. The VOX feature will automatically close the microphone after you finish speaking. "

Thanks,
Bill.

 

[Rhino]

Need more info. You say when there's a passenger in the back. Does this mean whenever a headset is plugged in back there, only when they speak, etc? Is it only when a mic is keyed or activated by VOX? If it's whenever a headset is plugged in, have you tried a different headset? Is this a new problem that just showed up, or has it always been there? If it's new, was anything changed in the aircraft about the time the noise started popping up?

Without further information, this sounds like an induced noise issue in the rear cockpit wiring. If that's the case, this might help:

Ground Loops and Noise in Aircraft Systems

Quite a few forum threads and articles have at various times addressed ground loops, and their potential to cause noise or other interference in your avionics system. Simply put, a ground loop occurs when different paths to ground are used. The difference in resistance, or impedance, on those...

forum.flydynon.com

 

[maddog]

Bill, I'm sure you've thought of this, but I had similar experience. One of my passenger audio jacks had rotated in its mounting bracket and caused one of the terminals to contact a ground. Only made noise when the jack was in use.
Carl

 

[Bill RV4]

Thanks all. New aircraft. First time taking a PAX. When PAX is wearing a headset (David Clark H-10-13.4) Not talking or transmitting. Ambient sound breaks through activates the microphone. Cant adjust the squelch to cut it out. From the Dynon manual:-

2. Adjust the squelch until you no longer hear background noise.

I do not have enough adjustment in the squelch.
I do not fly with the headset in the back with no PAX.
Cheers
Bill.

 

[Rhino]

The SV-INTERCOM-2S only has one squelch control. If it's working for the front cockpit, it's working. As I said, you likely have an induced noise issue in the rear cockpit wiring, or in the headset itself. Another, considerably less likely cause is a fault with the VOX circuitry for the rear cockpit. I can't make a determination there, because I have no idea how the internal circuitry of the SV-INTERCOM-2S is designed, but I know there are different channels for pilot and copilot. But that isn't likely to be addressed until you eliminate the other, more likely causes. If you want to absolutely know if it's one or the other, disconnect the rear cockpit wires at the intercom and temporarily connect a headset cord. Just use a different headset when you do that, so you don't end up creating the same problem with an incompatible headset. That's the difficult route to go though. I'd start by first just using a different type of headset in the rear cockpit. If that ends up being the problem, you probably won't have to do anything with the plane.

In reference to the headset, I use the word incompatible deliberately, because the headset doesn't necessarily have to be bad to cause this. Some pilots have reported their Bose A20 microphones are too sensitive for their SV-INTERCOM-2S, and they keep activating VOX. I know of one that solved that problem simply by adding an extra foam cover over the microphone. I doubt that would work for everyone though.

 

[airguy]

Couple things - try a different headset, and see if there is an air vent somewhere that is blowing onto the microphone in the back. Also try adding a mic sock on the rear microphone if you don't already have one. They do make a difference.

 

[RVDan]

When mixing headsets sometimes the mic gains aren't the same. It could be that the mic gain is too high and that makes the mic break the VOX squelch. Try adjusting the mic gain down a bit and see if you can get both mics within an acceptable range.

 

[Bill RV4]

"Try adjusting the mic gain down a bit and see if you can get both mics within an acceptable range."

Ok, thanks for that. How and where do I adjust the mic gain?

 

[Rhino]

I don't think the H-10-13.4 has a mic gain adjustment.

 

[Bill RV4]

Yes, so , even wearing that particular headset in the front with nothing in the back, I have the same problem. I will find another headset to try.
Thank you to all who have helped me.

 

[airguy]

Yes, so , even wearing that particular headset in the front with nothing in the back, I have the same problem. I will find another headset to try.
Thank you to all who have helped me.

Ahhh! Progress!

 

[Rhino]

Ahhh! Progress!

And the easiest fix too.