On 9/29/2017 1:30 PM, Don W7WLL wrote:
To begin, I have zero experience with a fan dipole. I’ve read what I could find
but see there are a number of variables to consider and not all are in agreement (not
unusual) on feedpoint arrangement and separation.
I've used 80/40 fan dipoles for years with great success. All have been
"flat," supported between trees. Construction is simple and cheap -- I
use spreaders cut from 1/2-in PVC conduit. They're about a foot long,
with holes cut a half inch or so from each end. The antenna wire is bare
copper, and I solder a smaller bare copper wire around each insulator to
hold it in place along the line. That wire is needed only on the longest
element (in this case, 80M). The longest wire should be rigged on top,
because it must support the dipole.
There should be little interaction between the two bands, except that
the lowest frequency band will exhibit its "normal" SWR bandwidth, but
the bandwidth of the higher frequency element will be about half as much
as usual. This is not much of a problem, because 40M is fairly narrow as
a percentage of the frequency.
I've also successfully used 3-wire fans for 20, 15, and 10. For those, I
used spacers that were 15-18-in long, and made the center wire the
support wire.
I've also fed a 2-band loaded (so it could be shorter) dipole for 80 and
40 and fed it with some vintage (but brand new on a spool) Belden 75 ohm
KW Twinlead that I found at a hamfest in Milwaukee many years before. it
was up about 40 ft, and I loaded it as Tee vertical by tying the two
sides of the feedline together and using a big wrought-iron fence as a
counterpoise. It worked better as a Tee vertical on 80 and 160 than it
did as a horizontal dipole on 80.
Note that you CANNOT use a ferrite choke (often called a "current
balun") at the feedpoint if you're going to load it as a Tee vertical --
doing so WILL fry the choke, even running as little as 100W.
73, Jim K9YC
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