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Wayne · May 3rd 12, 01:30 AM posted to rec.radio.amateur.antenna

wrote in message ...

wrote:
On 1 May,
wrote:

FYI I spent an afternoon with EZNEC exploring fan dipoles.

What I found was the farther apart the wires, the less the interaction,
which is what one would expect from common sense.

From my limited runs it appears that somewhere around 20 degrees is about
where the minimum separation needs to be for practical length
adjustments.

At angles less than that be prepared to spend a lot of time pruning.

It doesn't matter if the wires are separated vertically or horizontally
other than horizontal separatation means you need lots of support points.

If the bands are too close together, i.e. 20-17, 17-15, 12-10, you can
never get both bands to "work", i.e. a decent match.

I've got 12 and 10 working fine together, seperated by about 8" giving a
decent match. It also works fine on 15 although no wires for 15, but a
short
coax (20') to an ATU. It has a "pawsey stub" balun cut for about 17m
(modeled
with NEC for best match with fan dipoles for all bands 20 -10, but I
haven't
as yet got round to dipoles for 15 and below).

# I was refering to the case where there is nothing to adjust the match and
# getting something under 3:1 at the end of the feed line.
#
# Given an ATU, you can usually match anything and there is no need for the
# physical complexity of a fan dipole.

An open wire fed dipole would give pretty good performance. But, feeding
such an antenna with RG-8 and living with a high VSWR (maybe up to 10:1)
shouldn't be discarded.

A dipole of about 18 feet would cover 24 and 28 MHz with about 5:1
VSWR....not bad.