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Internal Antennas

Posted By:
Andrew King
Vintage Aircraft Association Member
#1 Posted: 2/22/2011 21:03:43

Are there any comm antennas that will work inside a fabric covered tube-and-rag fuselage?

Will this work?:






Ron Wanttaja
#2 Posted: 2/22/2011 23:03:05

Any time you put metal between the antenna and the receiver, it reduces efficiency.  Putting the antenna inside a steel cage (e.g., tube fuselage) will hurt the performance.

There are people who have probably gotten it to work, but the odds are against you.  I've got an antenna inside *my* fuselage, but mine is wood....

Ron Wanttaja
Nick Myers
#3 Posted: 2/23/2011 08:20:31

Just about any antenna (designed for radio comms that is) internal to a fabric aircraft should not be a huge issue, afterall, I have used a handheld inside my metal aircraft, with borderline dead batteries with moderate success.

That said, any time you are doing RF kind of stuff in a non-metal aircraft be prepared to deal with ground plane issues.  some sort of ground plane is required for most installations to work effectively.  In at least some experimental aircraft I have seen, this is done by providing a larger metal plate inside the fabrick to mount the base of the antenna to.  This provieds both the structural support to hold the antenna and provides the required ground plane.

Brian Anderson
Homebuilder or Craftsman
#4 Posted: 2/24/2011 19:05:09

Beware of the claims of "high gain". A dipole is a dipole and provided it is properly matched to the coax feed line it will perform exactly the same as any other dipole. The advantage of a dipole is that it eliminates the need for a  ground plane [and in general is a little easier to match to the feed line].

In theory the dipole should be mounted vertically, which may not be possible in many fuselages. However, it is also possible to curve or even bent the elements to fit the space available. In a metal tube aircraft this is likely to be a limiting factor because somewhere or other the elements are going to end up close to some tubing, and the performance is going to be degraded.

The technique works well in glass or wooden aeroplanes. It may be satisfactory in a tube and fabric fuselage but the only way to tell is to do some tests of performance. It is impractical to use a dipole on the outside of a fuselage.

Richard Warner
Homebuilder or CraftsmanAirVenture Volunteer
#5 Posted: 2/24/2011 19:34:50

I mounted a VHF antenna in an Aeronca Champ fuselage.  It is mounted  on a piece of aluminum that mounted to some of the lower tubing.  It is used with a portaqble tranceiver, and the performance is better than with just the portable radio's antenna.  Its mounted back in the fuselage below and behind the baggage bin.  It worked and I'm not messing with it.

Anthony Creasy
Homebuilder or Craftsman
#6 Posted: 2/24/2011 20:33:05

I have the exact antenna inside the rear fuselage of a J3, and it works great connected to my hand-held.  The challenge is finding enough room to mount as much vertical as possible for the Comm channels.  You also need to not mount directly to the tubular frame.  I isolated mine from the metal tube by a very thin plywood.