Another Problem Radio

[IBob]

Starting a new thread to avoid confusing the existing thread with too many owners and issues:

 

I have an XCom radio and Zulu headsets in my Savannah.

Engine is Rotax 912 and fitted with the large electrolytic smoothing capacitor. I also ran a negative cable from battery to a central point behind the instruments at time of build.

 

The radio/headset arrangement works fine, I am told I am very clear, also receive clearly, except on takeoff or climb at full throttle, when I get a lot of hash over any incoming calls and have to reduce power and ask for a repeat: reducing to 5000 - 5100RPM and the hash vanishes.

 

So, this looks like being engine noise(?) I would welcome suggestions as to where to start and in what order to come at this. Thanks.

(PS I note on the other radio thread references to turning the mic down in the Zulu headsets. At this point I have made no adjustments at all to the headsets or the radio.)

[FlyBoy1960]

Start by identifying where the noise is coming from. It is pretty simple; use the intercom on/off/isolate switch to turn the Intercom to the off position.

 

If the noise instantly stops then it tells you that you need to raise the squelch level on the intercom which needs to be adjusted higher until the noise goes away.

 

If the noise stays there exactly the same then you need to turn up the radio squelch until the noise cuts out.

 

If you can't cut out the noise using the radio squelch whilst the intercom is turned off then you have to look for other problems.

 

When I had the XCOM installed in my aircraft I had a similar problem and contacted the technical people. They told me to do exactly this but the only extra thing which they mentioned is that when the radio gets really warm the squelch will adjust by itself marginally because the tolerances inside change between cold and hot. Once I had the squelch worked out and realised there were two completely different sources of squelch and I adjusted it when it was hot it never needed adjusting again for the time that I had the aircraft. It was a great little unit and had a fantastic receiver sensitivity, I could hear things when I was flying on trips with other people that they couldn't hear. For example I could pick up the ATIS more than 100 miles away and they were struggling to get it with their Garmin and Microair at 30 miles.  I was very happy with this XCOM radio

Edited April 2, 2021 by FlyBoy1960

[IBob]

Thanks for that, FlyBoy. I believe this happens with the intercom off (too) but I do need to check that.

I will certainly check both squelch settings.

 

To be clear, I don't get this hash on takeoff or full climb until there is incoming radio from someone else.

(I haven't yet checked if it is there when I transmit too.)

 

 

[FlyBoy1960]

thanks for the clarification, if it only happens when you receive does it happen at idle, that cruise and at full throttle or is it a different level of sound or is it the same in all three engine settings

[IBob]

It only happens at full throttle. At cruise settings it's all good. See my first message.

And while I'm most aware of it on receive, it may be that it also affects my transmit, I haven't taken steps to check that.
I should add that these are receives of local transmits (may even be in circuit with me) so it's not a matter of distant weak signals.

[Blueadventures]

I had same on Trig. exactly noise on take off full throttle.   Adjusted internal factory setting squelch level and all good.

[IBob]

Blueadventures, I'm getting hash over incoming calls when at full throttle. Without incoming calls all is quiet. Is this what you had?

 

The Xcom offers radio squelch and intercom squelch. I adjust the first as required, have not adjusted the intercom squelch.
If my understanding of squelch is correct (and it may not be) adjusting squelch would stop the noise, but would do so by stopping the incoming calls?
What I'm wanting is to hear those incoming calls, but without the hash I get at full throttle.

[Blueadventures]

No, only on takeoff and no incoming calls. Slight misread of your situation. Cheers and have a good Easter.

Edited April 2, 2021 by Blueadventures

[spacesailor]

There Was a small piece of electronics, back in the CB days.

a small device taking the chirp or dot out of the receiver. it removed most of the Hash, & gave a clean sound.  a bit like a noise cancelling head phone .

spacesailor

[Kyle Communications]

Bob before you start looking too far. using Lightspeeds with Xcom radio you MUST turn the mic gain down on the mic itself. There is a small plastic plug in the body of the mic itself. Turn it pretty much all the way back to nothing just off the bottom. Then go into the radio adjustments and adjust your audio out on transmit...or by also listening at your sidetone but that also is a different adjustment. Best is go to "the numbers"..have someone listen on another radio and adjust the audio on the mic input on the xcom. The mic gain inside the lightspeeds is huge..you need to cut it back....you could be getting a resonance noise from the prop being picked up though the mic. Adjust the headset first...then look for a problem if there is one

 

[IBob]

Thanks Flyboy, Blueadventures, Spacesailor and Mark.

I'll do as Mark suggests and start with the headset mic adjustment, since this does seem to be a required adjustment with the Lightspeed/Xcom combination.

It will be good if it turns out to be that simple!

I'll post here again when I have a result.

[Kyle Communications]

I have done it on quite a few lightspeed xcom combinations where guys were having issues...do that first then see... 🙂

Also the squelch setting does drift...from memory mine when cold was 17 to just mute the radio but after 10 mins or so the squelch would trigger I ended up leaving it at 19 and the temperature drift was compensated

 

[FlyBoy1960]

Yes, i was always cold plus 2 as the final setting, you just leave it at that. You wont loose hearing people because its so sensitive.

[IBob]

Hi Mark et al.

I had a first stab at adjusting the mic trim today:

 

On the ground, engine off, 1 headset only, I first listened to myself with the intercom on.
I then turned the mic pot down as suggested:  minimum is 8oclock, max 5oclock/it was set at 12oclock, and I set it back to 9 oclock.

Once I did this, performance was very intermittent, with my voice dropping out or not picking up at all, and no amount of fiddling with the radio mic amp setting or squelch seemed to fix it.

 

In the end I factory reset the radio to be sure I was back to basics, set the mic pot to 11oclock, where it did seem stable but quieter, and since it was a perfect day, went flying.

This is a low traffic area, so I was not aware of any transmits on takeoff or hard climb: which is to say I have no idea if my slight reduction in mic trim has made any difference.

 

I wonder if Lightspeed have altered something in their design so that the mic output is better matched, and doesn't require so much turn down?

It would also be nice to know when the Xcom picks up any alterations to it's parameters: immediately/on exiting that part of the menu/on cycling of power? It doesn't say. It does say not to mess with the radio mic setting, as this will change the whole behaviour of the radio....