I have a 100 foot of Rohn 25G and a couple of monobanders for topload. I
originally ran three, quarter slopers via a remote switch box. Rarely did
I see any big difference when switching from one to another. I finally
removed two of them. The sloper works pretty well as I have managed to
work over 200 countries with it. In hind sight I should have added an
equal length of coax to each one of the slopers. This would have added
reactance to the unused slopers causing them to look like reflectors. It
might have been a much better performer. The real trick to making a sloper
perform (one or multiples) is to locate the attachment point an approximate
electrical quarter wavelength down from the top of the tower. In other
words the sloper is one half of a dipole while the "upper" portion of the
tower (from the feedpoint, up) would be the electrical equivalant of the
other half of the dipole. This approximation can be modeled with software
(I use EZNEC), or you can cut the sloper to a calculated length and attach
it in normal fashion. Measure the feedpoint and resonant frequency (using
a very short piece of coax) with an antenna analyzer. Move the sloper
attachment point down the tower a few feet and measure again. If the
resonant frequency is going in the desired direction, repeat as necessary
until you have a resonant antenna at the desired frequency. I generally
find the feedpoint to be around 40-60 ohms requiring no matching device.
If the feedpoint is much higher/lower you may want to use a tuner or UNUN
for a good 50 ohm match. A few turns of coax or some ferrite will help to
keep RF off the coax shield.
de Gary W0AW
Wayne Rogers <n1wr@chesapeake.net> on 09/11/98 03:59:29 PM
Please respond to n1wr@chesapeake.net
To: towertalk@contesting.com
cc: (bcc: Gary R. Hosler/MIPP/Imation)
Subject: [TowerTalk] 160M Inverted Vee vs. Half Slopers
I Have 90' of Rohn 25G with a TH-7 on top, three feet above the flat-top
top section.
Top set of guys are philystran.
I have a top ten devices relay panel at top of tower and am
contemplating
what is best (better?) approach for using this installation to support a
160
meter antenna.
My first thought was to put up two or three Half slopers. After reading
up
some on half slopers, I'm wondering if one (or maybe two, at 90 degree
angles) inverted vees might be a more effective antenna. My interest is
both
DX and stateside.
Any input will be greatly appreciated.
Thanks. Wayne, N1WR, Lusby, MD
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