---------------------------------------------------------- Avionics-List Digest Archive --- Total Messages Posted Tue 01/15/08: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 12:41 AM - VHF Transmitting Noise (Garlick, Bill (W.D.)) 2. 08:08 AM - Re: VHF Transmitting Noise (Noel Loveys) ________________________________ Message 1 _____________________________________ Time: 12:41:52 AM PST US Subject: Avionics-List: VHF Transmitting Noise From: "Garlick, Bill (W.D.)" Hi I'd appreciate some comments or advice from avionics installers who half-understand what they're doing? (My limits are that I need to follow manufacturers' installation instructions and wiring diagrams to the letter; and if something doesn't quite work I'm at a complete loss!...Although if any advice was something like connecting a xxx ohm resistor in parallel in a particular circuit, I could manage to cope with that). I have just installed an ICOM IC-A200 transceiver coupled with a PS Engineering PM501 Intercom in a newly built Vans RV7, and when I press the PTT switch I get a lot of noise feeding-back into the earphones as I'm talking... The Air Traffic Controllers say they're reading me "fives", and the noise doesn't occur when Receiving or when using the voice-activated intercom. The noise isn't in time with the engine, but is constant whilst transmitting and sounds like wind blowing across the microphone. Any ideas about what could be wrong? Thanks BillG ________________________________ Message 2 _____________________________________ Time: 08:08:31 AM PST US From: "Noel Loveys" Subject: RE: Avionics-List: VHF Transmitting Noise What you have described sounds a lot like alternator whine coming into your audio panel. If it is, you should be able to remove it by installing a choke in the power line to your PN501. A choke is simply a coil and a capacitor, in parallel, tuned to remove alternator frequency sound. It is wired in series in the B+ line of your audio panel and it stops the noise which is coming in on that wire. Where to get the choke depends on the registration of your plane GA will have to get it from an avionics shop, others, from an electronics or amateur radio outlet. A lot of AB owners can get a lot of free help from local amateur radio ops. They really know what they are doing form a practical point. Also check the wires between your transceiver and audio panel have the shield grounded only at one end. The last piece of advice is the one that is a pain... When you get your system working draw up a little block interconnect diagram of exactly what you have there so if you have future problems you will have an idea where to look. You can start on that interconnect diagram ASAP even before installing a choke. Better avionics shops won't put a finger on an installation until they have finished their interconnect diagram. Doing that makes for less mistakes in installation and much less problems. Things to include in the interconnect diagram are wire connecters and fuse locations. Hope this helps Noel From: owner-avionics-list-server@matronics.com [mailto:owner-avionics-list-server@matronics.com] On Behalf Of Garlick, Bill (W.D.) Sent: Tuesday, January 15, 2008 5:10 AM Subject: Avionics-List: VHF Transmitting Noise Hi I'd appreciate some comments or advice from avionics installers who half-understand what they're doing? (My limits are that I need to follow manufacturers' installation instructions and wiring diagrams to the letter; and if something doesn't quite work I'm at a complete loss!...Although if any advice was something like connecting a xxx ohm resistor in parallel in a particular circuit, I could manage to cope with that). I have just installed an ICOM IC-A200 transceiver coupled with a PS Engineering PM501 Intercom in a newly built Vans RV7, and when I press the PTT switch I get a lot of noise feeding-back into the earphones as I'm talking. The Air Traffic Controllers say they're reading me "fives", and the noise doesn't occur when Receiving or when using the voice-activated intercom. The noise isn't in time with the engine, but is constant whilst transmitting and sounds like wind blowing across the microphone. Any ideas about what could be wrong? Thanks BillG ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message avionics-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Avionics-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/avionics-list Browse Digests http://www.matronics.com/digest/avionics-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.