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Excessive noise on VHF radio when Transmitting

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hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Tue Jun 14, 2016 1:40 pm Post subject: Excessive noise on VHF radio when Transmitting

Gentlemen,

  

 I have a noise problem on the VHF radio system in my plane when I attempt  to transmit. In fact The other day while flying through Class C airspace the  approach controller was telling me that my transmission was broken and had so  much noise he could hardly understand what I was saying. I also hear the noise  in my headphones when I transmit, not when receiving.

  

 I have visually checked all the ground connections on the plane and they  are clear of corrosion and are tight. While on the ground with the engine not  running the radio transmission is fine with no problems. The problem only occurs  when the engine is running. The noise sounds like the frequency of the rotating  generator on the back of the engine which is a Rotax 912 UL. The audible  frequency can be heard to vary with the engine rpm. It is “dirty” noise. My  radio is a panel mounted  ICOM IC-A200. I also have two 10,000 mF  capacitors connected in parallel between the voltage regulator and ground as  noise filters. I have visually checked the two capacitors, and they seem to be  in good order (i.e. no swelling or distortion). The antenna is a Comant VHF CI  121 using a quarter wave ground plane. I have had no problems with  this system for ten years.

  

 Here are the specifics:

 Aircraft    Allegro 2000 LSA

 Engine    Rotax 912 UL

 TSN        741 hrs

 Radio     ICOM IC-A200

 Antenna    Comant VHF CI 121

  

 Any and all advice as to how to identify what is causing the problem and  how to correct it would be appreciated.

  

 Hugh G.  McKay III, P.E.

N661WW

email  hgmckay(at)bellsouth.net

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Brian Carpenter

Joined: 06 Mar 2008
Posts: 26
Location: TAYLOR, AZ

Posted: Tue Jun 14, 2016 3:08 pm Post subject: Excessive noise on VHF radio when Transmitting

Check the ground connection on the antenna. Mine has some silver tape on the inside of the fiberglass to make your ground, possibly use ohmmeter to see if that ground connection has broke somehow. Possibly the final output transistors on the radio itself may be bad and you're putting out very low power so the noise covers the amount of audio going out. Possibly check the outgoing power of the radio. May have to be done at an avionic shop. 



Sent from my Brian's iPhone

On Jun 14, 2016, at 14:39, Hugh McKay <hgmckay(at)bellsouth.net (hgmckay(at)bellsouth.net)> wrote:

 	  Quote: 	
		      Gentlemen,

  

 I have a noise problem on the VHF radio system in my plane when I attempt  to transmit. In fact The other day while flying through Class C airspace the  approach controller was telling me that my transmission was broken and had so  much noise he could hardly understand what I was saying. I also hear the noise  in my headphones when I transmit, not when receiving.

  

 I have visually checked all the ground connections on the plane and they  are clear of corrosion and are tight. While on the ground with the engine not  running the radio transmission is fine with no problems. The problem only occurs  when the engine is running. The noise sounds like the frequency of the rotating  generator on the back of the engine which is a Rotax 912 UL. The audible  frequency can be heard to vary with the engine rpm. It is “dirty” noise. My  radio is a panel mounted  ICOM IC-A200. I also have two 10,000 mF  capacitors connected in parallel between the voltage regulator and ground as  noise filters. I have visually checked the two capacitors, and they seem to be  in good order (i.e. no swelling or distortion). The antenna is a Comant VHF CI  121 using a quarter wave ground plane. I have had no problems with  this system for ten years.

  

 Here are the specifics:

 Aircraft    Allegro 2000 LSA

 Engine    Rotax 912 UL

 TSN        741 hrs

 Radio     ICOM IC-A200

 Antenna    Comant VHF CI 121

  

 Any and all advice as to how to identify what is causing the problem and  how to correct it would be appreciated.

  

 Hugh G.  McKay III, P.E.

N661WW

email  hgmckay(at)bellsouth.net (hgmckay(at)bellsouth.net)



 

<Hugh.vcf>

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_________________
BRIAN N3081X

N456TS

Joined: 15 Aug 2015
Posts: 70

Posted: Wed Jun 15, 2016 8:26 pm Post subject: Re: Excessive noise on VHF radio when Transmitting

There are two main noise sources when the engine is running.  Generator and spark plugs.  I would check all grounds again.  Do you have a good meter which can measure capacitance?  Sometimes electrolyte caps can dry out without puffing.  You could confirm your noise source by disabling the generator and running the engine.  Does the static become better/change when running on only one ignition?

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N456TS

hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Thu Jun 16, 2016 6:12 am Post subject: Excessive noise on VHF radio when Transmitting

N456TS,



How do I disable the generator on a Rotax 912?



Hugh G. McKay III, P.E. Fellow, L.M. ASCE

Senior Consultant

Worldwide Engineering Inc.

4090 North NC Hwy. 16

Denver, NC 28037



Ph. 704-661-8271

Fax 704-483-5466

email hgmckay(at)bellsouth.net

http://www.wwegeo.com

--

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N456TS

Joined: 15 Aug 2015
Posts: 70

Posted: Tue Jun 21, 2016 6:00 pm Post subject: Re: Excessive noise on VHF radio when Transmitting

 	  hgmckay wrote: 	
		  How do I disable the generator on a Rotax 912? 	




Sorry for the delay in reply.  You can disconnect the two "G" wires at the regulator.  Tape and isolate them from touching anything including each other.

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N456TS

N456TS

Joined: 15 Aug 2015
Posts: 70

Posted: Mon Jul 04, 2016 8:26 am Post subject: Re: Excessive noise on VHF radio when Transmitting

Did you find your static source?

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N456TS

hgmckay

Joined: 23 May 2006
Posts: 397

Posted: Tue Jul 05, 2016 4:38 am Post subject: Excessive noise on VHF radio when Transmitting

N456TS,



I have been busy with family, the holiday and other matters since my last 

communication. I will resume the search hopefully this week.



Hugh G. McKay III, P.E. Fellow, L.M. ASCE

Senior Consultant

Worldwide Engineering Inc.

4090 North NC Hwy. 16

Denver, NC 28037



Ph. 704-661-8271

Fax 704-483-5466

email hgmckay(at)bellsouth.net

http://www.wwegeo.com

--

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