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nuckolls.bob(at)aeroelect
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 Posted: Sun Sep 27, 2020 3:53 pm Post subject: Can radials of home made ground plane be tapered? |
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At 03:41 PM 9/27/2020, you wrote:
Okay, my copy is rev B and doesn't speak to adding
a ground plane.
I'm a bit mystified by this requirement. The gps/waas
antennas are active devices meaning that the rf samples
from the 'ether' are non-resonant 'probes'
that cannot deliver useful energy into a 50-ohm coax
without electronic (active) augmentation . . .
nor do they have the same capture area of a tuned
and/or multi-element antenna. Ground planes cannot
participate in the delivery of energy to the active
antenna's feedline . . . only in shaping radiation
(reception) patterns.
We've got all manner of gps devices from wrist
watches and little drones to telephones and
cameras. All must depend on active antennas,
in horribly challenging environs . . . no
room for a really efficient antenna.
Now we have a gps system on the backbone of
an airplane, completely free of terrestrial
noise and shadowing with an uncluttered view
of the sky . . . yet the installation instructions
speak of 'optimizing' performance with the
addition of a ground plane under an active
antenna? Hmmm . . .
What's missing from these documents is any
calibration on bang-for-the-buck. I.e. just
how much do I gain with this optimization?
There's a whole bunch of hocky-puck, gps
antennas flying with no ground plane. It
would be interesting to install both
configurations on an airplane with an A-B
switch . . . to observe just how much
optimization is secured with addition
of the ground plane.
I'd be surprised if the optimization offers
more than a little wiggle in the already
more-than-adequate signal strength displays.
Thanks for the update on the manual . . .
Bob . . .
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donjohnston
Joined: 13 Dec 2009
Posts: 231
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| Posted: Mon Sep 28, 2020 5:15 am Post subject: Re: Can radials of home made ground plane be tapered? |
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I would have to agree. I've had the antenna for a GTN625 installed in a fiberglass airplane with no groundplane for 5 years and never had a problem with reception.
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nuckolls.bob(at)aeroelect
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nuckolls.bob(at)aeroelect
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| Posted: Sun Oct 04, 2020 9:45 am Post subject: Can radials of home made ground plane be tapered? |
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At 11:43 AM 9/28/2020, you wrote:
| Quote: | --> AeroElectric-List message posted by: "rparigoris" <rparigor(at)hotmail.com>
Hi Group FWIW I called Garmin and Stein Air and both said to use a ground plane. I also called Vans. On their RV-12 they install the GA-35 on a small bracket FWF. I called them and asked about a ground plane and they said that the lower cowl acts as a ground plane. |
Not one of those assertion suggest that
there is any DATA to support the recommendation.
| Quote: | Here's a post from a guy in the Vans Forum: "I can tell you this...originally
I installed mine under the cowl with little to no ground plane. It worked.... |
Not necessarily 'hard' data but certainly
compelling . . .
| Quote: | Later I installed a bigger ground plane and the signal levels definately increased." It was posted in reply from a 12/30/2012 question in Vans Forum, he doesn't say what model plane he had, precisely what antenna or how large of a ground plane. I have now heard of several Europa's and a Long EZ using the GA-35 without a ground plane with good success. Ron P.
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Interesting. I'm not suggesting that a ground
plane under a gps antenna is not beneficial,
only wondering if it's observably useful.
I recall discussions on the amateur built forums
in years past about adding a ram-air induction port
to the airplane's cowl. I seems some builder made
some valid measurements of available manifold pressure
with and without such a feature. He opined there was value
in fabricating one.
I think the discussion died out when
an engine guru reminded us that airspeed
goes up the cube root of h.p. and the fractional
improvement for the addition would be difficult
to measure much less observe in actual practice.
Methinks the GPS ground plane may fall into
this category as well. There are millions
and millions of GPS based appliances that
perform as advertised with exceedingly
'deficient' antennas. It seems that somewhere
between the least and the best, there is
a demonstrable configuration that would save
OBAM aircraft builders hours of no-value-added
effort on their project.
Bob . . .
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