---------------------------------------------------------- Avionics-List Digest Archive --- Total Messages Posted Mon 04/06/09: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 01:54 PM - Airframe used as antenna? (user9253) 2. 04:29 PM - Re: Airframe used as antenna? (Doug McNutt) 3. 04:54 PM - Re: Airframe used as antenna? (Noel Loveys) ________________________________ Message 1 _____________________________________ Time: 01:54:32 PM PST US Subject: Avionics-List: Airframe used as antenna? From: "user9253" On an aluminum airplane such as a Van's RV or Zenith 601XL, is it feasible to use part of the airframe as a VHF com antenna? I am thinking of parts like the landing gear or roll bar or vertical stabilizer. Has anyone done any experiments along these lines? Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=238035#238035 ________________________________ Message 2 _____________________________________ Time: 04:29:37 PM PST US From: Doug McNutt Subject: Re: Avionics-List: Airframe used as antenna? At 13:53 -0700 4/6/09, user9253 wrote: >On an aluminum airplane such as a Van's RV or Zenith 601XL, is it >feasible to use part of the airframe as a VHF com antenna? I am >thinking of parts like the landing gear or roll bar or vertical >stabilizer. Has anyone done any experiments along these lines? It surely is possible. But safe and legal? Probably not. The problem is that a metal part you choose to use as the radiator won't work if it's grounded to the rest of the airplane. Designers and FAA rules like "bonding" between all metal parts to reduce radio interference and to prevent sparks that might ignite something. Required bonding would make an antenna fail. You could think about using tuned or just inductive bonding straps that would act as insulators in the frequency band of interest. You might also think about a negative antenna. It's possible to cut a long skinny hole in, say, a vertical stabilizer in a way that the absence of metal, in the ground plane that is the rest of the surface, can be excited as an antenna. I have personally done that, at 244 MHz, in tail fins of sounding rockets but I suspect it would be a PITA in an airplane that needs not to develop cracks in its skin. If a major part of the aircraft is fiberglass anyway you might get away with using an aluminum framing part that is inside. -- --> A fair tax is one that you pay but I don't <-- ________________________________ Message 3 _____________________________________ Time: 04:54:33 PM PST US From: "Noel Loveys" Subject: RE: Avionics-List: Airframe used as antenna? Problem there is the airframe is grounded to the battery and from there the case of the transmitter etc. The radiator for the antenna needs to be insulated from contact with the ground or it will short circuit. Of course you can put a big resistor across the feed line and the frame of the plane and turn the whole thing into a dirt big dummy load. That won't hurt your transmitter but you won't be heard either. The ground is still needed as a ground plane which directs the outbound signal. Sorry to tell you the best thing is still the vertical 1/4 wave antenna... for a metal plane. Noel -----Original Message----- From: owner-avionics-list-server@matronics.com [mailto:owner-avionics-list-server@matronics.com] On Behalf Of user9253 Sent: Monday, April 06, 2009 6:23 PM Subject: Avionics-List: Airframe used as antenna? On an aluminum airplane such as a Van's RV or Zenith 601XL, is it feasible to use part of the airframe as a VHF com antenna? I am thinking of parts like the landing gear or roll bar or vertical stabilizer. Has anyone done any experiments along these lines? Joe -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=238035#238035 ------------------------------------------------------------------------------------- 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.