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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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 Posted: Mon Apr 06, 2009 12:53 pm Post subject: Airframe used as antenna? |
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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
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Joe Gores |
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douglist(at)macnauchtan.c
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| Posted: Mon Apr 06, 2009 3:29 pm Post subject: Airframe used as antenna? |
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At 13:53 -0700 4/6/09, user9253 wrote:
| Quote: | 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?
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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 <--
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Mon Apr 06, 2009 3:54 pm Post subject: Airframe used as antenna? |
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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
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user9253
Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan
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| Posted: Tue Apr 07, 2009 4:56 am Post subject: Re: Airframe used as antenna? |
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Thanks to Doug and Noel for your replies. The consensus seems to be that the simplest, easiest and safest is to use the 1/4 wave ground plane antenna.
Joe
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Tue Apr 07, 2009 6:23 am Post subject: Airframe used as antenna? |
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With a good clean connection to the ground plane.
Noel
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