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Today's Topics:
1. Rohn/Radian (Fred Spinner)
2. RE: Delrin End Insulators (Noel)
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Message: 1
Date: Wed, 1 Sep 2004 10:40:27 -0500
From: Fred Spinner <fred.spinner@gmail.com>
Subject: [TowerTalk] Rohn/Radian
To: towertalk@contesting.com
Message-ID: <a1e06807040901084079edafb8@mail.gmail.com>
Content-Type: text/plain; charset=US-ASCII
Oh, when I was negotiating for a building permit for my tower, the
county wanted a drawing not in Rohn's catalog. I emailed Rohn/Radian
asking if a drawing was available for what the county was asking.
They said no and offered to have a PE there do it for $250.
(Reasonable price too for a couple hours of a PE's time.)
This was all within 3 hours of when I sent the first e-mail. Luckily
I talked the county out of it ($250 is $250!), but if that is an
example of Rohn's new service under Radian, I think hams will be very
happy with them in the future.
Fred W0FMS
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Message: 2
Date: Wed, 1 Sep 2004 09:44:04 -0600
From: "Noel" <yaesurig@msn.com>
Subject: RE: [TowerTalk] Delrin End Insulators
To: "'Michael Tope'" <W4EF@dellroy.com>, "'TowerTalk'"
<towertalk@contesting.com>
Message-ID: <000201c4903a$82d61e70$0200a8c0@home>
Content-Type: text/plain; charset="iso-8859-1"
I used to operate/maintain some very large HF RLPs that use delrin
insulators. Freq range 3-30 MHz and power is over 5KW. Many of these
antennas have been in use for over 20 years. I know cause I installed
several of em. Little different than a fan dipole but we never had any
problems with moisture absorption. We had a problem with UV resistance
and they'd crack after a few years. But the manufacturer corrected that
and we haven't had a problem since. If you have insulators that absorb
moisture, you probably don't have delrin or they've changed from those
I'm familiar with.
Regards
Noel
Mike wrote:
--SNIP: Delrin is a fairly lossy dielectric at HF frequencies (DF = .027
at 1 MHz) and it also is quite prone to moisture absorption. Should I be
concerned at all about this. I am not very concerned about the center
insulator since the impedance at that point is low. A quick calculation
seems to confirm this. If we assume about 5pF of stray C from the center
insulator, a 70 ohm feedpoint impedance, and 1.5 KW at 4 MHz, a DF of
027 would correspond to about 350 milliwatts of dissipation in the
center insulator. Not enough to even cause a noticeable rise in
temperature. Perhaps water absorption might make this worse, but I don't
know if that will have much effect at 4MHz.
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End of TowerTalk Digest, Vol 21, Issue 4
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