Brad,
There is NO SUCH THING as a NON-resonant length of wire.
The lengths listed in the ARRL Antenna Books are typically
resonant in-between the conventional amateur bands. For
example 27 ft which falls between 15 and 20 M but IS self
resonant on 17M, or 40 ft which is between 20 and 30 M
but is ONE FULL WL on 12M, or 56 ft which is ONE FULL
WL on 17M.
Another point which many people miss is that the resonance
is LOWERED by a factor of 2 when connected to the tower.
This is because you have continuity from the first insulator,
through the tower, to the first insulator on another guy.
A friend placed his first insulators 10 ft out on his guys which
were 10 ft below a tribander. He commented that the antenna
played very well on 10 and 20 but seemed to be lacking 'punch'
on 15M. I suggested that his guys formed a 15M DIRECTOR
10 ft BELOW the DE of this tribander, directing 15M energy
STRAIGHT DOWN. (10 + 1 + 10 = 21 ft conductor directly
below the tribander).
I place my first insulators as close to the tower as possible,
typically 3 to 4 ft, then space insulators 12 ft, 12 ft, 27 ft,
followed by combinations of 27 or 40 as height demands.
If WARC bands are a concern, then more 12 ft lengths should
be used since 12 ft is resonant above 30 MHz and therefore
'nearly' invisible on ALL HF bands.
K7GCO has stated that it is necessary to isolate the guys
for roughly the first 1/2 WL on the lowest frequency of
ALL the antennas on the tower (i.e. lower guys need to
be broken up also, especially if you have side mounts).
The alternatives are Phillystran or Fiberglass. Phillystran
stretches more than steel or fiberglass which can cause
greater stresses in the tower, especially with long lengths.
Unfortunately, the fiberglass guy manufacturer requires 5000 ft
minimum orders. They are willing to split orders for multiple buyers.
Tom N4KG
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