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rtitsworth
Joined: 16 Jan 2006
Posts: 76
Location: Detroit, Mi
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 Posted: Thu Aug 23, 2007 10:35 am Post subject: Homemade 1/4 wave Comm Antennas |
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Bob,
In Ch13 of the Connection you describe how to make a ¼ wave Comm antenna with 4-10 1” copper strips as the ground plane. You also briefly describe a center “commoning disk”.
Question:
How big can/should the center communing disk be?
What happens if the center disk is ~11” radius (~1/2 the size of the strips)?
Does this tend to mess-up the resonant length/properties of the strips?
If said antenna is being placed on the belly of a composite aircraft with various metal items in direct proximity overhead (flap motor, aux fuel pump, flap mechanism, avionics bay, etc), is there anything that should be done to help “shield” the antenna (and/or ground plane strips) from the effects of the metal items overhead?
Rick
[quote][b]
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nuckollsr(at)cox.net
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| Posted: Thu Aug 23, 2007 12:00 pm Post subject: Homemade 1/4 wave Comm Antennas |
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At 02:32 PM 8/23/2007 -0400, you wrote:
| Quote: | Bob,
In Ch13 of the Connection you describe how to make a ¼ wave Comm antenna
with 4-10 1 copper strips as the ground plane. You also briefly describe
a center commoning disk .
Question:
How big can/should the center communing disk be?
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What ever is convenient. A commoning disk with a
radius equal to height of antenna, then you have
a contiguous, "ideal" ground plane. If you make
it too small, it serves no purpose as a doubler.
Someplace between ideal and too small, it provides
a convenient point to tie off the radials -AND-
possibly a reinforcing effect of skin around
the antenna.
| Quote: | What happens if the center disk is ~11 radius (~1/2 the size of the strips)?
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No problem.
| Quote: | Does this tend to mess-up the resonant length/properties of the strips?
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The tips of ground plane radial strips are
measured from base of antenna to tip of radial.
The larger the commoning disk, the shorter
the radial. Think of it as starting with an
ideal disk and then cutting away as much
material as practical to provide an effective
ground plane, effective doubler and minimum
weight. Something on the order of 6" in diameter
and 4-10 radials is a reasonable compromise.
| Quote: | If said antenna is being placed on the belly of a composite aircraft with
various metal items in direct proximity overhead (flap motor, aux fuel
pump, flap mechanism, avionics bay, etc), is there anything that should be
done to help shield the antenna (and/or ground plane strips) from the
effects of the metal items overhead?
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No. The proximate effect of a ground plane is
to attenuate (shield) the antenna from conductor/
noise effects on the opposite side.
Bob . . .
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