My 80/40/20 dipole fans (EW & NS) were up for a few years and now as
80/40 fans are used for FD, one recut CW the other SSB. My spreaders
are 1/2" square grey pvc from McMaster (maybe TAP Plastics). I found
spacing tips about 20" was enough and it helped to space feedpoints
about 3" vertically on a small piece of acrylic plastic. Now when they
get put away, they are wound on 10" diameter cardboard concrete forms
which keeps all the wires and ropes in order.
The Cebik modeling advice re having transmission lines connecting the
feedpoints together makes NEC yield good results. Also align segments
as best you can, the usual advice for close space wires.
Grant KZ1W
On 2/18/2020 06:34, Ignacy Misztal wrote:
The simplest design by FAR for 2 band dipoles is folded skeleton sleeve
made of ladderline. See links to QST article in
http://www.highonsolder.com/ham-radio/folded-skeleton-sleeve-antennas/
I use one as non-directional antenna for contesting. It is 20/10 design
with an extra wire in the middle of the ladderline for 10m. Weighs next to
nothing and no mechanical complexity. Now up for 10 years with no
maintenance.
I used to have a commercial 160/80/40 dipole with coils, with a fan dipole
for 30m. Constant maintenance of spreaders. Dismal performance on 160/80m
compared to a 80m doublet fed by ladderline. But it had low SWR at
resonance.
Ignacy, NO9E
On Mon, Feb 17, 2020 at 2:42 PM Jim Brown <jim@audiosystemsgroup.com> wrote:
On 2/17/2020 11:12 AM, Jeff Widen via TowerTalk wrote:
I want to add a 20 meter wire to my 30 meter dipole and am looking for
suggestions for spreaders to separate the elements. Half inch PVC pipe
seems to bulky and heavy, any suggestions for something lighter that will
hold up to the sun? Also what is the best separation distance?
Hi Jeff,
Over the years, I've made good use of fan dipoles. 1/2-in PVC conduit
cut into short lengths is what I've always used. I've built fans for 80
and 40, for 20, 15 and 10, and for 40, 30 and 17. Now that I have good
Al in the air for 20-6M, my only fan is for 80 and 40. I use a spacing
of roughly 9-12 inches, with holes drilled into the spacers for wires to
run through. For the longest element, I use #9 bare copper, with a wire
jumper soldered around the spacer to hold it in place. The shorter
element is #12 THHN, and can be held in place at each end by cable
clamps or split bolts. Spacers are roughly 6 ft apart. That 80/40 fan
has been up 120 ft or so suspended between redwoods for at least 10
years. The spacers aren't as pretty as they were when I built it, but
they haven't broken. They get plenty of UV exposure here in NorCal.
The #9 bare copper was obtained by buying a spool of #8 bare copper from
the big box store and stretching it by tying one end of a 200 ft length
to the base of a tree and the other end to the trailer hitch of W6GJB's
pickup and pulling VERY slowly until it breaks. Glen and I have done
this several times after I first learned it from WA6NMF about 15 years
ago. What you end up with is close to hard drawn copper, roughly 20%
longer than what you started with.
The only trouble I've had with fans is when something broke in a major
storm, dropping one end, and the fan got tangled in a big madrone.
Madrones are beautiful trees, but they're death on wire antennas. :)
In a fan, the SWR bandwidth of the shorter element will be reduced by
about half, while the SWR bandwidth of the longer element is that of a
single wire dipole.
Two of my fan dipoles are shown on pages 25 and 26 of
http://k9yc.com/LimitedSpaceAntennasPPT.pdf
73, Jim K9YC
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