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Radio noise when transmitting

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markdonahue

Joined: 16 Dec 2012
Posts: 16
Location: bainbridge island washington

Posted: Mon Mar 16, 2020 10:42 am Post subject: Radio noise when transmitting

I have an RV 9A aircraft with a 60 amp Plane Power alternator and an Icom IC-200 radio.  I recently installed ADSB (echo UAT/FYX-EXT) with associated antennae at recommended spacing on the plane’s belly.  My recent symptoms are a high whine in the headset when transmitting on the radio.  I hear incoming radio transmissions clearly.  I checked disconnecting the alternator by opening the field circuit breaker and the sound during transmitting goes away.

This issue may be more noticeable while on the ground.  When announcing “ready for take-off” I get a response from fellow pilots in the pattern that they hear a high whine in the transmission.  However when at 3000 ft altitude and 5 miles from the field during a radio check, the sound in my head set is diminished and the response from fellow pilots is “loud and clear”.  The fact that this occurred after the ADSB installation may be unrelated.  I don’t remember this problem immediately after that installation, so this may be a canard. Any advice on how to trouble shoot this and recommended fixes that I could attempt.

Thanks to this group.  I enjoy and appreciate the knowledge and experience of the members.

Mark Donahue

206 755 1093

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Mark Donahue

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Mar 16, 2020 3:24 pm Post subject: Re: Radio noise when transmitting

Make sure that the microphone jacks are electrically insulated from the airframe

with dielectric washers.  The mic ground wire should be grounded at the radio end only.

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Joe Gores

markdonahue

Joined: 16 Dec 2012
Posts: 16
Location: bainbridge island washington

Posted: Mon Mar 16, 2020 6:06 pm Post subject: Re: Radio noise when transmitting

I spoke to Allen (at) Hartsell (owner of Plane Power now) and he thought it could well be a bad diode on the alternator.  Suggested testing between the alternator output to ground with a volt meter set to AC voltage.  If I get something closer to 1 volt, as opposed to say .08 volt, then that would show a bad diode.  Also suggested checking the grounds.  I plan to do that.  Thanks for the suggestion on the headphone jacks isolation washers.  I will check that also.

Mark

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Mark Donahue

echristley(at)att.net
Guest

Posted: Tue Mar 17, 2020 5:09 am Post subject: Radio noise when transmitting

Also, try adjusting the volume on your headset, if it has a volume control. I had an issue of a squeal on transmit. I think the headset was picking up the transmitted signal and amplifying it back out. Problem went away when I turned the headset volume down

Sent from Yahoo Mail on Android

 

  	  Quote: 	
		    On Mon, Mar 16, 2020 at 7:27 PM, user9253

<fransew(at)gmail.com> wrote:

 

  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>



Make sure that the microphone jacks are electrically insulated from the airframe



with dielectric washers.  The mic ground wire should be grounded at the radio end only.



--------



Joe Gores

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nuckolls.bob(at)aeroelect
Guest

Posted: Tue Mar 17, 2020 9:13 am Post subject: Radio noise when transmitting

At 01:39 PM 3/16/2020, you wrote:

  	  Quote: 	
		  I have an RV 9A aircraft with a 60 amp Plane Power alternator and an Icom IC-200 radio.  I recently installed ADSB (echo UAT/FYX-EXT) with associated antennae at recommended spacing on the plane’s belly.  My recent symptoms are a high whine in the headset when transmitting on the radio.  I hear incoming radio transmissions clearly.  I checked disconnecting the alternator by opening the field circuit breaker and the sound during transmitting goes away.

 This issue may be more noticeable while on the ground.  When announcing “ready for take-off” I get a response from fellow pilots in the pattern that they hear a high whine in the transmission.  However when at 3000 ft altitude and 5 miles from the field during a radio check, the sound in my head set is diminished and the response from fellow pilots is “loud and clear”.  The fact that this occurred after the ADSB installation may be unrelated.  I don’t remember this problem immediately after that installation, so this may be a canard. Any advice on how to trouble shoot this and recommended fixes that I could attempt.

 Thanks to this group.  I enjoy and appreciate the knowledge and experience of the members.

 Mark Donahue

 206 755 1093 	


 --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 Make sure that the microphone jacks are electrically insulated from the airframe

 with dielectric washers.  The mic ground wire should be grounded at the radio end only.



 --------

 Joe Gores



    Joe's suggestion is a good one. Alternator whine

    is almost always conducted into transmitted audio

    by a ground loop caused by mounting the microphone

    jack to airframe without and insulating washer.



  https://tinyurl.com/t4kveee



    A possible reason for the noise going away while

    airborne: Alternator currents flowing on the

    airframe are greatest when alternator loads are

    heavy. Just after start, the battery is being

    recharged which adds to noise source. After

    a few minutes recharge, airframe currents

    are reduced.



    If you already have these washers, then the

    hypothesis is moot. Diode failures are rare.

    Let us know what you discover.



 

 

   Bob . . .

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