Today's Message Index:
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1. 10:08 AM - Archer style wingtip antenna fabrication questions (Charlie England)
2. 01:15 PM - Re: Archer style wingtip antenna fabrication questions (user9253)
3. 01:58 PM - Re: Re: Archer style wingtip antenna fabrication questions (Charlie England)
4. 08:48 PM - Re: Archer style wingtip antenna fabrication questions (Robert L. Nuckolls, III)
5. 08:57 PM - Re: Re: Archer style wingtip antenna fabrication questions (Robert L. Nuckolls, III)
Message 1
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| Subject: | Archer style wingtip antenna fabrication questions |
I have an Archer wingtip comm antenna I intend to install in one wingtip
(can always add a 1/4 wave whip if needed), and I'm thinking about building
the nav version detailed in Bob's 'Antennas & Feedlines chapter for the
other wingtip (figure 13-12 in my document).
How critical is the material for the .032" x .8" x 3.25" bakelite insulator
that forms what I'm guessing is a matching capacitor? Does the bakelite
participate in any way in operation, or is it simply a way to get a fixed
air gap?
Bakelite in that 'thinness' doesn't seem to be available without paying
more for shipping than the 3-postage-stamp size needed would cost. What
about substituting something like the thin HDPE cutting board stock,
available at discount stores? Two layers would be about .034" thick.
Thanks,
Charlie
Message 2
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| Subject: | Re: Archer style wingtip antenna fabrication questions |
Charlie, It looks like the critical dimension is the 0.31 air gap. My concern
is that a softer plastic will flow over time resulting in the screws loosening
up.
It looks like the angle part of the antenna is fastened to an aluminum wing rib.
The directions are not specific. A Bakelite sheet on eBay costs $5 including
shipping. Item #: 281793575532 from China. You might have to wait up to a
month for shipping. It is 1mm thick which converts to 0.039". I would not sand
it down. The Bakelite could possibly contain asbestos.
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=502533#502533
Message 3
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| Subject: | Re: Archer style wingtip antenna fabrication questions |
On 6/22/2021 3:14 PM, user9253 wrote:
>
> Charlie, It looks like the critical dimension is the 0.31 air gap. My concern
is that a softer plastic will flow over time resulting in the screws loosening
up.
> It looks like the angle part of the antenna is fastened to an aluminum wing rib.
The directions are not specific. A Bakelite sheet on eBay costs $5 including
shipping. Item #: 281793575532 from China. You might have to wait up to
a month for shipping. It is 1mm thick which converts to 0.039". I would not
sand it down. The Bakelite could possibly contain asbestos.
>
> --------
> Joe Gores
Your ebay-Foo is obviously better than mine; all the hits I got were for
much thicker stuff.
Thanks for the link!
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Message 4
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| Subject: | Re: Archer style wingtip antenna fabrication questions |
At 12:03 PM 6/22/2021, you wrote:
>I have an Archer wingtip comm=C2 antenna I intend
>to install in one wingtip (can always add a 1/4
>wave whip if needed), and I'm thinking about
>building the nav version detailed in Bob's
>'Antennas & Feedlines chapter for the other
>wingtip (figure 13-12 in my document).
>
>How critical is the material for the .032" x .8"
>x 3.25" bakelite insulator that forms what I'm
>guessing is a matching capacitor? Does the
>bakelite participate in any way in operation, or
>is it simply a way to get a fixed air gap?
>
>Bakelite in that 'thinness' doesn't seem to be
>available without paying more for shipping than
>the 3-postage-stamp size needed would cost. What
>about=C2 substituting something like the thin HDPE
>cutting board stock, available at discount
>stores? Two layers would be about .034" thick.=C2
It IS critical . . . yes it forms the dielectric
for a capacitor used to series resonate the feeder
strut.
Bob must have conducted experiments to optimize
the characteristics of that capacitor with respect
to the matching strut for optimal mid-band impedance
match.
If it were my project, I'd use ANY available dielectric
material and conduct experiments over a ground plane
on the table to achieve (1) antenna resonance and
(2) best match to the feed line.
When I was a kid, a 'gamma match' was commonly
used to bring a feed line and antenna radiator
into functional harmony. The attached figure
illustrates an adjustable feeder strut paired
with a variable capacitor to feed a grounded
quarter-wave antenna.
My 10M, 2-element beam had such a feature that
was tuned with the aid of an SWR bridge. Today,
a vector network analyzer is the instrument
of choice and can cost less than a good SWR
meter.
After getting close on the bench, you can
confirm on the airplane to see if 'tweeking'
is called for. I've had readers assemble the
Archer wing tip antennas per drawings but found
it useful to trim dimensions per measured results.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 5
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| Subject: | Re: Archer style wingtip antenna fabrication |
questions
At 04:01 PM 6/22/2021, you wrote:
><ceengland7@gmail.com>
>
>Your ebay-Foo is obviously better than mine; all the hits I got were
>for much thicker stuff.
>
>Thanks for the link!
I've got some fiber reinforced pvc
sheet that would be suitable for your
needs. Drop me a mailing address and
I'll send you some scraps to play with.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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