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hgmckay
Joined: 23 May 2006
Posts: 397
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 Posted: Tue Jun 14, 2016 1:40 pm Post subject: Excessive noise on VHF radio when Transmitting |
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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
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| Posted: Tue Jun 14, 2016 3:08 pm Post subject: Excessive noise on VHF radio when Transmitting |
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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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N456TS
Joined: 15 Aug 2015
Posts: 70
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| Posted: Wed Jun 15, 2016 8:26 pm Post subject: Re: Excessive noise on VHF radio when Transmitting |
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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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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Thu Jun 16, 2016 6:12 am Post subject: Excessive noise on VHF radio when Transmitting |
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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
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| Posted: Tue Jun 21, 2016 6:00 pm Post subject: Re: Excessive noise on VHF radio when Transmitting |
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| 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 |
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N456TS
Joined: 15 Aug 2015
Posts: 70
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| Posted: Mon Jul 04, 2016 8:26 am Post subject: Re: Excessive noise on VHF radio when Transmitting |
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Did you find your static source?
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N456TS |
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hgmckay
Joined: 23 May 2006
Posts: 397
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| Posted: Tue Jul 05, 2016 4:38 am Post subject: Excessive noise on VHF radio when Transmitting |
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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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