Must have put up a dozen of these things. As mentioned by another poster, they
can be a little tricky to tune but work fine once set up.
Tips:
Finding UV-resistant spreaders can be a problem. I've had good results with
"120" size film spools. If there is a professional photo lab in your town,
they may give them to you. The spools have the advantage of being very light
weight, cheap, UV resistant, and space the wires about 2 7/16". Have used
these devices since the early 80's.
Some folk have used "window" ladder line and just cut off the un-wanted piece.
Tried this and was disappointed. REAL tough to tune and the wind load from the
solid pieces of the "window" line caused the thing to flap around in the wind
and twist around itself.
Found weight to be a major concern. Most of the fan dipoles I made were for
80-40m. I made the 40m wire from much smaller gauge wire than the 80m wire as
it does not need to support itself or the feedline.
Construction tips:
Cut the 40 meter wire about 3' longer than calculated to allow for ease of
construction and ease of tuning.
The trick is to put parallel wires (about half the 80 meter wire and the 40
meter wire) under tension together so the spreaders will smoothly slide to
their positions without kinking the dipole wires.
I like to use about 18-24" spacing between spreaders. Thread the spreaders
onto the parallel wires before clamping both ends of the parallel wires and
putting the parallel wires under tension. Make up a spacing board such that
when it is placed between the 80 and 40 meter dipole wires, the length of the
board placed against the spreader you have just finished, will be correct for
the spreader you are going to install. Typically, you would work from right to
left, using the just secured right hand side spacer, run the board up against
it and then place the left hand spacer in position. The spacer board should be
wide enough to just fit in between the dipole wires so as to keep the spreaders
at vertical when the dipole wires are horizontal. Also, spreader spacing will
be uniform which makes for better appearance.
I drill holes in the spreaders big enough for the antenna wires to pass through
without snagging and use a #20 solid bare "tie wire" to hold the antenna wire
in place. I use 4 turns on each end of the tie wire over the top or bottom of
the spacer and have had no failures even without soldering. Take it easy when
tightening the tie wires, you want some movement so gravity will tend to hold
the 40 m wire down. If the tie wires are soldered, there may be a hindrance to
gravity's movement of the 40 meter wire.
Tried holding the wires in place with hot melt glue which was a complete
failure.
For an 80-40m "fan" dipole, I've had the best results using the 80 meter wire
as a catenary which supports itself and the 40m wire hanging below it on
spacers. At the center insulator, the 80 meter wire connects mechanically and
electrically to the center insulator and the 40m wire is just connected
electrically. A right triangle is formed at the center insulator with the 80
meter wire being parallel to the ground and the 40 meter wire coming up at an
angle from the first spreader to meet and connect with the 80 meter wire at the
center insulator.
Tuning:
80 meters first, then 40.
It is unlikely the spreader spacing will allow the length of the 40 meter
wire's resonance to coincide with the placement of a spreader. I just let the
excess drop down vertically.
Be Well,
Tim
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