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RotaxEngines-List: Excessive noise on VHF radio when Transmi

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Guy Buchanan
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Joined: 16 Jul 2006
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PostPosted: Tue Jun 14, 2016 6:40 pm    Post subject: RotaxEngines-List: Excessive noise on VHF radio when Transmi Reply with quote

Visually checking the antenna grounds isn't going to cut it. I'd refresh them manually. I have to do this once a year at least. (Stainless bolt on aluminum antenna base. Not great.)

2nd guess is pre-existing ground loop is now picking up charging noise due to a weakness in the system elsewhere. (Grounds?) You gotta be religious about ground loops.

Guy Buchanan
Assistant Scoutmaster – Troop 680
[url=mailto:gebuchanan(at)]gebuchanan(at) (gebuchanan(at)[/url]
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On 6/14/2016 2:39 PM, Hugh McKay wrote:

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.
email hgmckay(at) (hgmckay(at)

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Guy Buchanan
K-IV 1200 / 912Uls / Warp / 500 hours and flying again.
Now a glider pilot too.
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