Problem with headset when transmitting

[Owi]

Hi all,

 

I'm having a strange problem that involves my David Clark X11 headset and I'm hoping that someone here may be able to help.

 

Lately, using my headset, when I press the transmit button everybody on the frequency hears this high-pitched squealing noise. This is obviously untenable and my instructor has to do the radio work for me.

 

We've tried all the different switch settings, the same happens with or without the batteries. It was intermittent the week before but yesterday I could not get it to work at all.

 

I'm not sure if I can just send it in since I bought it second hand from someone and I don't have the original receipt. It is out of warranty - assuming its a standard 1 year.

 

Thanks in anticipation.

 

 

[djpacro]

Interim advice pending the avionics experts' responses - clean the plugs and clamp a ferrite core to the lead.

 

 

[Owi]

Thanks, gents.

 

Don, I did track down Peter's email and now, based on your response, I feel very much encouraged to contact him and see how we go.

 

Cheers,

 

 

[kaz3g]

Hi all,I'm having a strange problem that involves my David Clark X11 headset and I'm hoping that someone here may be able to help....

Hi Owi

 

What type of VHF are you using? I've been having a similar problem with my Pilot headset transmitting using the button on my stick and the intercom turned on. But if I plug my headset into the jacks for the pax and press that transmit button all is fine.

 

It's also fine on my side if I turn the intercom off.

 

I fitted ferrite plugs (thanks Dick Gower) but it still does it.... curious -O:"

 

kaz

 

 

[.Evan.]

Hi all,I'm having a strange problem that involves my David Clark X11 headset and I'm hoping that someone here may be able to help.

Lately, using my headset, when I press the transmit button everybody on the frequency hears this high-pitched squealing noise. This is obviously untenable and my instructor has to do the radio work for me.

 

We've tried all the different switch settings, the same happens with or without the batteries. It was intermittent the week before but yesterday I could not get it to work at all.

 

I'm not sure if I can just send it in since I bought it second hand from someone and I don't have the original receipt. It is out of warranty - assuming its a standard 1 year.

 

Thanks in anticipation.

Thanks for reminding me, Owi! I have the same problem with my Altronics headset (purchased second hand - but in excellent condition) and the Microair M760.

 

It's fine for intercom stuff, but the minute I press the transmit button it screams! Tried every combination of volume settings, etc.

 

Haven't had a chance to try it in another aircraft yet.

 

 

[Guest Andys@coffs]

So the usual reason for squealing on Tx is RF Feedback. Ultimately too much RF is being fed back into the mic circuit. Ferrites are a possible solution, but they need to be placed as close to the mic input connectino on the transceiver as possible. just puting it on the headset lead leaves the rest of the wiring from the jack back to the transceiver to collect the RF and feed it into the mic input section on the radio. Ferrites cost very little, so try a few in a few locations, close to the transceiver and close to the headset itself, if an active headset (ie active noise reduction) then that circuitry may be the source of the squealing necessitating a ferrite close to the headset.

 

Another option is to look at sheilding thos cables better than they might already be, (they may be audio standard sheilding only, of dubious value at VHF) or not sheilded at all. The usual convention is to ground the shield at one end, and leave it floating (unconnected) at the other end.

 

If it was fine before, and suddenly has just started have a look at the Antenna circuit to make sure that a connection or earth hasnt broken resulting in a high SWR which will induce higher levels of feedback than would normally be the case.

 

Ultimately the location of the antenna may be the issue, further away from you and the transmitter can be an issue in transmission losses, but ultimately RF power decreases by a squared function for each doubling in distance so a relatively modest increase in seperation can be significant.

 

Chasing down RF EMI can involve lots of guess work and good luck. Once I solved a similar issue in a trike, where the antenna was only 3ft away from the pilot and 2ft away from the M760 by wrapping a wiring loom in kitchen alfoil and then twisting on an earth connnection.... what ever it takes. (PS alfoil was a think branded one, not the cheap crap coles/woolies brand.

 

Andy