nuckolls.bob(at)aeroelect Guest
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Posted: Tue May 24, 2016 3:33 am Post subject: Transponder and ADS Antenna Mounting Location Questions |
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At 09:57 AM 5/23/2016, you wrote:
Quote: | Wow�this inherent anal retentive desire I have to �do it right the first time� is a real pain in the butt!!!
>A wet string hung under the fuselage would probably do must fine in terms of performance for receiving ADSB squitter. KISS . . . disk of aluminum with a legacy monopole is cheap, easy, works good, lasts a long time.>
The Dynon manual sure made a big deal about the EXACT size and shape of the antenna in a composite�I was thinking that an aluminum airplane would certainly not be the exact size and shape� |
Exactly. The only time the size and shape has greatest
effect is for the 'resonant' or '1/4-wave radial' style
of ground plane which is, in fact, an array of 4 to many
1/4-wave resonators paralleled at the base of the antenna.
If that is not practical, then simply get as much aluminum
under the antenna as practical/possible . . . if that happens
to be the belly of a whole airplane, great! If it's limited
to 11.3 square inches of oddly shaped aluminum, you would
probably have to go to the antenna lab to measure the
real differences . . . in practice it's probably nothing
you will be able to observe.
Quote: |
Anyhoo�Bob to confirm your communication before I start cutting and gluing�
With respect to the ADS-B antenna�I would like to mount it under the canard essentially in the nose compartment wheel well area�do you suppose this would work? What size should the aluminum ground plane be? Disk or square or egg shaped?!?! |
Give it a try. Obviously, getting it outside with
all metals "below" the ground plane is ideal. But
a lot of builders have experienced satisfactory
operations of transponders from a variety of installations
inside the confines of a composite structure. Archer
Xpnder antennas glued to the inside of the tail
is a noteworthy example. In fact, if you can fit
an Archer antenna onto a mostly vertical section
of real estate, intuitively I think I'd give that
the highest probability for success. But if push
comes to shove, you can always fabricate the idealize
resonant ground plane disk and add the 'chin whisker'
to the airplane . . . yeah . . . butt ugly . . .
but what's a mother to do? There are folk's
with big sticks who insist on 'keeping us safe' . . .
Quote: |
With respect to the transponder antenna pointed down below the airplane (location under the back seat)�should I get rid of the current egg shaped ground plane or leave it as is? |
If it has been working well I see no need to
fiddle with it . . .
Quote: |
This is just like being married�I tell my wife�just tell me what to do and I will do it�I don�t have to think that way!!! |
Except this is just physics. The simple-ideas in
behaviors of energy and materials. It's that
energy stuff we can't see, touch or smell so
we're victim to and limited by a whole lot of
anecdotal and/or poorly reasoned supposition.
But go spend a few years chasing electrons
on airplanes with test equipment that can see,
touch and smell that energy and life gets
much more confident . . . maybe not easier but
at least less risky.
Bob . . .
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