Radio problem.

[spitfire]

Hi all,

just wondering if anyone can help with this problem? I fly a Skyranger with an Xcom radio, when transmitting I am getting a lot of noise coming back through my headset.

it is worse at higher rpm, especially at climb out, noticeable but not too annoying at taxi and not there before engine start. The engine is a Rotax 912 uls.

I use a light speed headset. Thanks.

 

 

[Downunder]

I was getting this when it was getting too hot.

Is it in a ventilated position?

 

[spitfire]

Hi Downunder, yes it’s in a cool spot, seems the same in winter...

[horsefeathers]

Are you using a USB style charger for your electronics (eg an iPad)?

Depending on the design of the charger, they can cause a problem with feedback thru the headphones

[RFguy]

what is sounds like to me is that :

The radio and or intercom generates sidetone, and the voltage at the radio or intercom, when the radio transmits is falling below the regulator dropout threshold, and it is unable to take noise off the avionics / power bus , and the noise on the power gets passed to the sidetone. 

Either the voltage to the system is LOW (has a high resistance) , OR the alternator is under heavy load (sick battery?, OR the alternator has lost a diode or soemthing and is generatijng a very coarse waveform.  OR you have a common earth with the alternator and should have a separate earth, IE an earth is missing, or the radio pass transistor for the power supply is sick maybe zapped by a voltage spike, OR.....

 

more information questions : answer all questions yes or no. 

 

when you say noise...
is this a whine proportional in pitch to RPM ?

is this a staic noise sound proportional in rate to RPM ?

Is your transmitted audio clean ?

Is the battery  known good ?

What is the battery /avionics voltage at idle and high RPM ?

Do you have this same noise between two headsets on the intercom ?

Does this occur with a NON NC headset- IE a headset without any electronics in it ?

Is there noise on the received audio?

 

 

 

[Blueadventures]

Hi If you one of the large 22,000 capacitors check that is still serviceable eg there may brown coloured fluid coming out of it or swollen / burst.  If so replace it.

[FlyBoy1960]

if the intercom is operating normally and the only time you are getting excessive noise is when you press the transmit button and all you need to do is turn down the sidetone. You want the side tone to match the same volume as the intercom that way you are getting level audio.

[spitfire]

4 hours ago, horsefeathers said:

Are you using a USB style charger for your electronics (eg an iPad)?

Depending on the design of the charger, they can cause a problem with feedback thru the headphones

Thanks, yes I do use a USB charger for the iPad, pcas and gps signal unit for the iPad.

i can easily check if these are an issue.....

 

[spitfire]

4 hours ago, RFguy said:

what is sounds like to me is that :

The radio and or intercom generates sidetone, and the voltage at the radio or intercom, when the radio transmits is falling below the regulator dropout threshold, and it is unable to take noise off the avionics / power bus , and the noise on the power gets passed to the sidetone. 

Either the voltage to the system is LOW (has a high resistance) , OR the alternator is under heavy load (sick battery?, OR the alternator has lost a diode or soemthing and is generatijng a very coarse waveform.  OR you have a common earth with the alternator and should have a separate earth, IE an earth is missing, or the radio pass transistor for the power supply is sick maybe zapped by a voltage spike, OR.....

 

more information questions : answer all questions yes or no. 

 

when you say noise...
is this a whine proportional in pitch to RPM ?

is this a staic noise sound proportional in rate to RPM ?

Is your transmitted audio clean ?

Is the battery  known good ?

What is the battery /avionics voltage at idle and high RPM ?

Do you have this same noise between two headsets on the intercom ?

Does this occur with a NON NC headset- IE a headset without any electronics in it ?

Is there noise on the received audio?

 

 

 

Thanks RFguy ,

ok the answers as best as I can think of;

1) no ,it’s not a whine noise at all.

2)Yes, it increases with rpm.

3) transmitted audio: I am told by other pilots when requesting a radio check that it’s a 4.

4) Battery is new.

5) I think the voltage at idle is about 14 volts, not sure at full song, will have to check.

6) No, noise is only on transmissions (When ptt activated)

7) Yes it occurs with a DC 13.4

8)No, recd audio is good.

[spitfire]

2 hours ago, FlyBoy1960 said:

if the intercom is operating normally and the only time you are getting excessive noise is when you press the transmit button and all you need to do is turn down the sidetone. You want the side tone to match the same volume as the intercom that way you are getting level audio.

Thanks Flyboy,

I’ll check that out

[spitfire]

4 hours ago, Blueadventures said:

Hi If you one of the large 22,000 capacitors check that is still serviceable eg there may brown coloured fluid coming out of it or swollen / burst.  If so replace it.

Thanks Blueadventures,

I’ll have a look

[rgmwa]

9 minutes ago, spitfire said:

Thanks RFguy ,

ok the answers as best as I can think of;

1) no ,it’s not a whine noise at all.

2)Yes, it increases with rpm.

3) transmitted audio: I am told by other pilots when requesting a radio check that it’s a 4.

4) Battery is new.

5) I think the voltage at idle is about 14 volts, not sure at full song, will have to check.

6) No, noise is only on transmissions (When ptt activated)

7) Yes it occurs with a DC 13.4

8)No, recd audio is good.

Sounds exactly like the static I get on transmit. I’m not sure that it increases with rpm although it probably does. I’ll check next time. All other checks match yours. Also readability 4. No noise with engine off. My radio is a Garmin SL40 and I’ve been trying to find the noise source too. Engine is also a 912ULS. Side tone is matched to volume. All suggestions welcome.

[RFguy]

All good information. Something we are missing here.

hmmmmmm,

 

and the intercom between the two pilots is good ?

Do two different types of headsets behave the same ?

 

"static" . as in just white noise ? like the same noise when the squelch is open on a radio  (with no signal) ?????

OR a pulsed static - noise ?

 

 

 

Edited November 25, 2020 by RFguy

[rgmwa]

Static as in squelch noise, no pulses. Headsets are not the problem. Intercom is good. Mic jack is isolated from the airframe. Headset jack isn’t - all as per plans for the RV-12. I suspect it may be an earthing problem, but where to start looking?

[RFguy]

ahhh . right . white noise.

 

Noise has to be produced somewhere to get into something else.

 

That sounds like the radio transmitter is opening an intercom headset mic squelch.  Just like when you adjust the intercom squelch so that microphones dont open the gate on the system when no one is talking.  That could be the transmit  signal getting into that system.  Now, metal plane. tick.

 

Two things to check :

 

1) *Check integrity of coax connector on rear of radio. . Check that the radio antenna has a good connection to the body of the plane at the antenna . The outer or braid or earth of the coax, must have a good connection to the body to avoid the coax becoming part of the radiating antenna.

 

The same applies at the radio end. check the outer of the coax plug has a good connection. With a multimeter then you can with the coax plug removed (if it does) that you have continuity to earth (because the coax shield will connect to the airplane body back at the antenna).

 

2) Could be an earth issue on the headset microphone circuits, or intercom system.  IE the shield that is not connected to the ground.  In audio, shields are often connected at only one end  , and if one end becomes disconnected, now shield. 

 

You could try and bridge the mic socket shield to the airplane body (ground) at the mic socket.  That might tell you something.

 

Glen 

 

[rgmwa]

Thanks for the suggestions. I’ll have a go. I did have an intermittent loud feedback squeal on transmit that has plagued me ever since the plane was built that I finally traced a few weeks ago to a loose nut on the antenna cable BNC connector that plugs into the back of the radio. Just needed tightening half a turn. I went from readability 2 to readability 4 so that was a good result. The cable was supplied with the kit so it wasn’t one of my dodgy wiring efforts. Now I sound no worse than many other aircraft I hear out there, but I’d really like to get rid of all the noise and have clear transmissions.

[Downunder]

I replaced the cheap black coax with RG400 and connectors from https://www.steinair.com/

RG400 doesn't bend the best, so took a bit of routing but I think my tx and rx is better.

[RFguy]

Some advice for the masses : 

 

RG400  (teflon ) is nice, but it wont make any difference to your radio signal. Zilch. nada.

 

Cheap  black coax RG58 from a reputable supplier  is just fine... as long as the maximum operating temperature is < 80 deg C.  That's the limitation . 

 

Advantages of the Teflon cable-  survives very high temperatures, 200C deg all day and night , and 400C deg for a short period. 

 

Also, dont bother with double shielded cable. It's a con unless you are working in a very high tech laboratory. And needs different connectors.

 

And stay away from single inner conductor cables , always use stranded inner conductor cables unless it doesnt move (or is restrained so it doesnt move) 

Dont squash the Teflon cable too much , it will cold flow, given time.

 

Glen

(yes I do this for a living) .

 

 

 

 

 

 

[M61A1]

Have you looked at adjusting the mic gain on the lightspeed headset? 

[rgmwa]

Like Spitfire, I'm also using a Lightspeed headset (Sierra). Haven't tried adjusting the mic gain yet. I've got an old passive headset so I'll see if that makes a difference.

[spitfire]

8 hours ago, RFguy said:

All good information. Something we are missing here.

hmmmmmm,

 

and the intercom between the two pilots is good ?

Do two different types of headsets behave the same ?

 

"static" . as in just white noise ? like the same noise when the squelch is open on a radio  (with no signal) ?????

OR a pulsed static - noise ?

 

 

 

Yes static / white noise , just like open squelch ......

[kgwilson]

Presumably all the suggested things like sidetone volume, USB interference, coax connections and earth loops etc have been checked. I had similar problems several years ago and found it was a combination of several things. The first was more than 1 earth (earth loop). There should be a single point of earth in the entire system and that is back at the radio & from there to the main earth bus back to the battery. Are all the cables shielded and by that I mean if you have 2 core cable is each core shielded? I changed all my cables to all single core shielded. Do you have a power filter on the power supply to the radio? That will get rid of any power induced noise. Do you have ferrite chokes on the audio cables by each connection like at the headsets, radio and PTT. And lastly are all the connectors good with no dry joint issues causing high resistance.

 

Once I'd done all these things noise disappeared and my radio is a Microair which does not have a great reputation.

[RFguy]

BTW if anyone has any dead Microair radios I am happy to buy them.

[FlyBoy1960]

52 minutes ago, RFguy said:

BTW if anyone has any dead Microair radios I am happy to buy them.

How many do you want ?    there are just about as many dead Microair radios at our airfield than there are rebuilt Jabiru engines !       

 

I know of about three or four and will ask the owner on Saturday when I am at the airport

[spitfire]

6 hours ago, M61A1 said:

Have you looked at adjusting the mic gain on the lightspeed headset? 

Yes , gain fully wound down