---------------------------------------------------------- Allegro-List Digest Archive --- Total Messages Posted Tue 06/14/16: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 02:40 PM - Excessive noise on VHF radio when Transmitting (Hugh McKay) 2. 04:08 PM - Re: Excessive noise on VHF radio when Transmitting (Allegro) 3. 07:40 PM - Re: RotaxEngines-List: Excessive noise on VHF radio when Transmitting (Guy Buchanan) ________________________________ Message 1 _____________________________________ Time: 02:40:14 PM PST US From: "Hugh McKay" Subject: Allegro-List: 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 =9Cdirty=9D 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@bellsouth.net ________________________________ Message 2 _____________________________________ Time: 04:08:13 PM PST US From: Allegro Subject: Re: Allegro-List: 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 i f that ground connection has broke somehow. Possibly the final output transi stors on the radio itself may be bad and you're putting out very low power s o the noise covers the amount of audio going out. Possibly check the outgoin g 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 wrote: > > Gentlemen, > > I have a noise problem on the VHF radio system in my plane when I attempt t o transmit. In fact The other day while flying through Class C airspace the a pproach 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 no ise in my headphones when I transmit, not when receiving. > > I have visually checked all the ground connections on the plane and they a re 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 o ccurs 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 a udible frequency can be heard to vary with the engine rpm. It is =9Cdi rty=9D noise. My radio is a panel mounted ICOM IC-A200. I also have t wo 10,000 mF capacitors connected in parallel between the voltage regulator a nd ground as noise filters. I have visually checked the two capacitors, and t hey seem to be in good order (i.e. no swelling or distortion). The antenna i s a Comant VHF CI 121 using a quarter wave ground plane. I have had no probl ems 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 h ow to correct it would be appreciated. > > Hugh G. McKay III, P.E. > N661WW > email hgmckay@bellsouth.net > ________________________________ Message 3 _____________________________________ Time: 07:40:07 PM PST US Subject: Allegro-List: Re: RotaxEngines-List: Excessive noise on VHF radio when Transmitting From: Guy Buchanan 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 680 760.809.6145 gebuchanan@cox.net www.troop680.org On 6/14/2016 2:39 PM, Hugh McKay wrote: > 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@bellsouth.net ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message allegro-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Allegro-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/allegro-list Browse Digests http://www.matronics.com/digest/allegro-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.