A little additional clarification. I haven't modeled this yet but are the
inductors deliberately lower Q, read "higher loss" to add some "R"
to perhaps 1) improve SWR bandwidth and F/B and/or 2) bring the
feedpoint impedance closer to 50 ohms? What I'm thinking of is in mobile
antennas (for 80 and 40 M) where the loading coil has a profound effect
on efficiency. However, mobile antennas are very short compared to a
wavelength and as the antenna gets closer to a 1/2 wave, the coil loss
is less important. The "Shorty forty" by CC is not that short and perhaps
the little extra inductor loss provides a better overall performance, or was CC
was just being cheap. That's what I'd like to find out.
I'm fully familiar with the various mechanical improvements published over
the years and intend to implement them. I put these up when they first
came out! It's a stack, 65ft and 130 ft. Mine have finally succumbed to
the rusty screws that plague this design.
Chuck...
-----Original Message-----
From: Chuck O'Neal [SMTP:coneal@ma.ultranet.com]
Sent: Friday, August 31, 2001 6:39 PM
To: 'Bill Hider (N3RR)'; towertalk@contesting.com
Subject: RE: [TowerTalk] Weatherproofing for copper coils?
Reinventing is what it's about! That old design was produced to be
cheap, that's why you had to rebuild yours. I'm sure the electrical
design is not optimized either. My question is simply to those
folks that may have realized this and I'm curious what they think.
I know the inductors are not optimized for Q but my question
is "Can the inductor design be improved such that the resulting
performance improvement is worth it?" I'm not sure and I'd
like to hear from others. I now have your opinion.
Thanks!
Chuck...K1KW
-----Original Message-----
From: Bill Hider (N3RR) [SMTP:n3rr@erols.com]
Sent: Friday, August 31, 2001 6:16 PM
To: Chuck O'Neal; towertalk@contesting.com
Subject: RE: [TowerTalk] Weatherproofing for copper coils?
UGGGGH!
Why re-invent the wheel? This is a 20 year old, PROVEN, antenna. Plenty of
articles tell you how to solve the problems you guys are asking about now.
Why not just follow them?
Go to Leeson's book and several QST articles, do what they tell you to do,
and be done with it. The inductance is well-known. Shrink wrap that costs
$2/foot is a BARGIN. So it will cost you $16 in shrink-wrap. It will solve
your problem easier than winding coils of unknown inductance and resuls.
What am I missing here?
Yes, I have two of these antennas up at 67/134 ft (stack). Yes, I beefed
them both up to QHS++ and added RR++ as well. Yes, I used additional shrink
wrap on the coils. Yes, they work magnificantly.
Bill, N3RR
-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of Chuck O'Neal
Sent: Friday, August 31, 2001 5:08 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Weatherproofing for copper coils?
I can't answer this question, but it brings up a question I had about
upgrading two of these antennas myself. I am contemplating doing the
same since they have become intermittent. My question is will the
tuning change if I replace the loading coils with better inductors having
lower loss even if the inductance remains the same. I intend to measure
the inductance and do something similar as Steve has asked. Either that,
or just beef up the connections and leave the loading coils alone. I wonder
what the real gain would be with better inductors. Perhaps there is a trade
off
between bandwidth and gain here?
Thanks!
Chuck...K1KW
-----Original Message-----
From: Steve Miller <millersg@dmapub.dma.org>
To: towertalk@contesting.com <towertalk@contesting.com>
To: <towertalk@contesting.com>
Date: Friday, August 31, 2001 4:58 PM
Subject: [TowerTalk] Weatherproofing for copper coils?
>
>Towertalkers,
>
>I am upgrading Cushcraft 402-CDs. The plan is to replace the stock
>loading coils with high-Q coils made from 1/4 inch copper tubing.
>I'd prefer to apply a low loss protective coating directly to the
>copper tubing rather than construct housings for the coils.
>
>Heat shrink tubing seemed a possible solution but finding the right
>combination of UV resistance, low RF loss, and price has been
>unsuccessful. (PTFE heatshrink has good properties but runs almost
>$2/foot.)
>
>Are there any low loss paints or coatings that adhere well to copper
>and can withstand a north Texas environment for several years?
>
>Any suggestions on how best to weatherproof the coils is welcome....
>
>
>Steve
>
>
>
>--
>Steve Miller N8SM millersg@dma.org http://www.dma.org/~millersg
>
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>-----
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