[TowerTalk] Re: TowerTalk Digest, Vol 21, Issue 4

[Bill Fuqua]

Naturally their towers cost more but Heights Towers has very good 
documentation along with detailed up to date structural analysis of the 
towers. http://www.heightstowers.com/

73
Bill wa4lav
At 12:00 PM 9/1/2004 -0400, you wrote:
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>Today's Topics:
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>    1. Rohn/Radian (Fred Spinner)
>    2. RE: Delrin End Insulators (Noel)
>
>
>----------------------------------------------------------------------
>
>Message: 1
>Date: Wed, 1 Sep 2004 10:40:27 -0500
>From: Fred Spinner <fred.spinner at gmail.com>
>Subject: [TowerTalk] Rohn/Radian
>To: towertalk at contesting.com
>Message-ID: <a1e06807040901084079edafb8 at 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
>
>
>------------------------------
>
>Message: 2
>Date: Wed, 1 Sep 2004 09:44:04 -0600
>From: "Noel" <yaesurig at msn.com>
>Subject: RE: [TowerTalk] Delrin End Insulators
>To: "'Michael Tope'" <W4EF at dellroy.com>,        "'TowerTalk'"
>         <towertalk at contesting.com>
>Message-ID: <000201c4903a$82d61e70$0200a8c0 at 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
>****************************************