[TowerTalk] Tuners

[Rob Atkinson]

Loops are over-rated unless they meet certain requirements.   I tried
a 75 m. 1 w.l. loop 30 feet high fed with ladder line and bal. tuner.
I thougt it was great but I was comparing it to worse antennas I had
used before.  That was one of my self-deception problems.   Hams get
into trouble with horiz. loops because they are so big compared to 1/2
w. dipoles that they expose more RF to ground coupling and loss,
unless they are put up pretty high to get them isolated.   So a 1 w.l.
loop on 80 m. say, has to be at least 70 feet high or loss to ground
starts to increase enough to be noticeable.   On high bands you get
(to plagarize some hams I know) the "spaghetti pattern"--lots of
useless weird lobes so it becomes a dice roll if you hit someone
right.  If you look at a 3-D plot of a modelled loop that is 6 or 8
w.l. long you see a real RF mess pattern.

Someone mentioned NVIS earlier.   NVIS is a military concept, intended
to provide quick reliable commo within a short range using lossy wide
bandwidth dipoles up 0.1 to 0.2 w.l.   That would be at east 50 feet
on 160.  the idea is a height that is low enough to be low profile and
easy to erect and provides an average height for cloud burner
operating.  Hams seem to have taken the height recommendations as some
sort of exaulted gospel from gov't researchers with Ph.D.s.  The gov't
designers may be compentent but they were not designing antennas for
hams; they were designing antennas for the Army and the Army does not
have a 1.5 KW U.S. power limit.  The Army also does not care about
loss to ground, due to close proximity coupling.   The one thing that
a ham may find desirable with a NVIS dipole is the 90 degree angle,
but that can be achieved at the lowest band of interest with a height
starting at 0.2 to 0.25 w.l. and at that height loss to ground is
dramatically reduced.

73

Rob
K5UJ