Today's Message Index:
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1. 08:12 AM - Re: Grounding radio antenna and transponder antenna (Argonaut36)
2. 10:46 AM - Re: Re: Grounding radio antenna and transponder antenna (Robert L. Nuckolls, III)
3. 07:27 PM - Re: Grounding radio antenna and transponder antenna (user9253)
4. 08:37 PM - Re: Grounding radio antenna and transponder antenna (Argonaut36)
5. 08:45 PM - Re: Grounding radio antenna and transponder antenna (Argonaut36)
Message 1
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| Subject: | Re: Grounding radio antenna and transponder antenna |
Thanks for your reply.
As far as the size of the ground plane, I am constrained by the small dimensions
of the airplane. The ground plane should be larger, but there is no much that
I can do about it.
I try to improve everything else in order to get more range and less static. When
you say that antennas do not necessarily have to be grounded to the airframe,
you seem to imply that it would be better to ground the antenna, even if it
is not indispensable. In my case, because of the ground plane issue, I would
take any improvements, doesnt matter how small. Could you please confirm that,
ideally, radio antennas should be grounded to the airframe and provide a reference
for that (book, website, paper).
Thanks
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=491316#491316
Message 2
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| Subject: | Re: Grounding radio antenna and transponder antenna |
You said tube structure . . . fabric or metal skin?
If fabric, a 5.6" alum disk .060 or so thick
is an appropriate ground plane.
Emacs!
If your fabric is 'tight' against a structural
tube, then the ground plane can go on the outside
surface. It would look cleaner if between skin
and tube. One or more clamps should secure the
ground plane to structure . . . not for electrical
'bonding' but for mechanical support.
Emacs!
Whether the ground is inside or outside the
skin, the antenna should mount in the center
with good electrical connection between antenna
base and the ground plane.
If metal skin, simply mount antenna to skin
but consider double of any practical size
to re-enforce the mounting surface to preclude
cracking around mounting hole due to aerodynamic
buffeting.
VHF comm antennas need good support to the
ship's tubular structure. If metal airplane,
ground antenna base to skin. If fabric covered
airplane, ground a suitable mounting plate
to the ship's structure then ground antenna
to the mounting plate. Ship's structure
becomes the ground plane.
Bob . . .
Message 3
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| Subject: | Re: Grounding radio antenna and transponder antenna |
Bob N. posted today
"One or more clamps should secure the
ground plane to structure . . . not for electrical
'bonding' but for mechanical support."
In my opinion (I am no antenna expert), it is not necessary to connect an antenna
ground plane to the airframe. However, the airframe could be used as a ground
plane if of sufficient size and shape.
Radio frequency current and DC current behave entirely differently. What is an
open circuit to DC could be a short circuit for radio frequency current.
An antenna ground plane does not necessarily have to be straight or flat. Nor
does it have to be a sheet of metal. Curved strips of wire or metal tape that
radiate outward from the antenna base could serve as a ground plane. Experiment
to find something that works.
http://www.aeroelectric.com/Reference_Docs/Antenna/
-
"ARRL Antenna Book" The 2 meter band is close to the aviation band.
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https://ia801600.us.archive.org/7/items/TheArrlAntennaBook/Hall-TheArrlAntennaBook.pdf[
--------
Joe Gores
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http://forums.matronics.com/viewtopic.php?p=491322#491322
Message 4
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| Subject: | Re: Grounding radio antenna and transponder antenna |
Bob,
Thanks for your post and for the sketch.
Please note that my airplane has a standard certificate. It is not experimental.
The antenna is mounted on a removable panel on the bottom of the airplane;
the antenna was installed professionally on the panel and I have not had any structural
problems in many years of flying. The panel is made of metal except
for a plexigas window and doubles as the radio antenna ground plane, even if
it is kind of small for that purpose. I have installed some metal tape that goes
over the plexigas trying to improve things. The panel is attached to a vertical
metal panel on each side with machine screws/anchor nuts. At the front,
the panel overlaps another metal panel and connects to a little beam with sheet
metal screws. At the back, the panel overlaps a fabric panel and connects
to a little beam with sheet metal screws.
As mentioned above, this panel is removable and needs to come out of the airplane
for maintenance purposes a few times a year. It would be difficult to make
modifications to this panel. I have noticed that the transponder antenna ground
plane is grounded to the plane tubular frame and I am just trying to establish
if the radio antenna panel should also be grounded or not and why.
Thanks for your help.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=491323#491323
Message 5
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| Subject: | Re: Grounding radio antenna and transponder antenna |
Many thanks for the additional information provided. I will go through the documents
linked to your post.
Please note that I have included additional information on my antenna set up in
my reply to the post of Bob.
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http://forums.matronics.com/viewtopic.php?p=491324#491324
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