---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 04/28/11: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 02:28 PM - Strange radio transmit problems - take 2 (Peter Pengilly) ________________________________ Message 1 _____________________________________ Time: 02:28:05 PM PST US From: Peter Pengilly Subject: AeroElectric-List: Strange radio transmit problems - take 2 In June last year I wrote about a problem I was having with the transmitter in my airplane where the radio would not transmit on some frequencies. I wonder if I could again ask for some advice? I thought I solved the problem by replacing the radio to antenna coax - but all I in fact did was shift the frequencies that were problematic. Since then I have tried several different fixes without any success. I have improved the grounding of the antenna, replaced the antenna and tried several different headsets, all with no change to the problem. I have found that on the ground without the engine running the radio will transmit on all frequencies (or at least in 1 MHz steps through the frequency band). In the air some frequencies cause a problem (such as 118.9, 125.25 and 127.05), but throttling back to idle sometimes produces an intelligible transmission, although not great. When the radio does not transmit it is obvious as no side tone is heard in the headset, sometimes carrier wave only is transmitted. The voltage regulator (PMR-1) for the SD-8 alternator is mounted very close ahead of the radio, along with the large capacitor and OV thing, I'm now wondering if there is some kind of electro magnetic interference happening? Of course the best check would be to go fly with the alternator off, and I should be able to do that over the next few days (there's some wedding going on here tomorrow that is getting in the way of everything ...). Assuming it is interference, how far away from the radio should I mount the VR, is the back side of the firewall a suitable location? Should the capacitor be close the the VR, or doesn't it matter? Its a Becker AR-4201 radio, Becker say that if it transmits on any one frequency there is nothing wrong with the radio. Transmit is good on some frequencies (for example 122.6, 129.8) and receive is always strong. Thanks for your help, in anticipation. Regards, Peter ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-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/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-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.