Dave:
If you decide to wind a coaxial balun, here's a link to the D40 manual
https://www.dxengineering.com/parts/csh-d40/documentation . Essentially, the
balun is 12 turns of non-foam dielectric coax wound on a 6 inch diameter form.
I wound my own balun for my D40 that's been up on the tower since 2001.
73 de
Gene Smar AD3F
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Dave
Sublette
Sent: Tuesday, September 19, 2017 12:40 PM
To: Dan Maguire via TowerTalk <towertalk@contesting.com>
Subject: [TowerTalk] 40M rotary dipole
I have spent the morning working on a 40M dipole made from leftover Telrex
parts. I took careful measurements of the lengths and diameters of tubing
entered the dimensions into Antenna Model. The 1.5:1 SWR bandwidth is 175
Khz and it centers nicely at 7075. The SWR rises only to 1.8:1 by the time you
reach 7.3 Mhz. I think it will work very well for me.
Mechanically, the antenna is a bit more limber than I thought it would be. I
will have to add stays to hold the elements up. I plan to use a double run of
3/16” dacron rope with small end insulators near the element. I would imagine
that when rain and ice arrive, those stays would affect the performance when
wet.
The thing is really big! I put up a rotary dipole for 80 meters once that was
shortened to 125 feet with end capacity hats. This antenna isn’t near what
that one was. The 80meter one was 125 pounds and this one will be only 27
pounds, not including the mount. But still, the 40M is a large antenna.
I’m now trying to decide whether to wind a balun or just coil a few coils of
the feedline to keep RF off of the coax. Do you have any preference?
thanks & 73,
Dave, K4TO
ps — my address system puts the name of an individual and then “via towertalk”
and the list address. I don’t know how it reads when you get it, but this is
addressed to the list, not an individual. I wish I could get to send just to
the generic tower talk email address.
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