At 12:58 PM 11/9/2005, [EMAIL PROTECTED] wrote:
Thoughts on my vertical
2. Got the HF2V vertical in place with 60 radials. Got it "mostly" tuned
up. Missing: Serious plan for more than 25 KHz of band coverage at a
time, esp. for upcoming CQ WW SSB and also covering both the DX Window on
SSB plus CW and maybe RTTY.
-- 25 kHz is about right for SWR bandwidth on a single vertical on 75/80,
unless there's some huge loss source to kill the Q.
-- You might seriously consider putting some sort of variable reactance at
the base of the antenna. The radiation efficiency of the antenna is
reasonably constant over the band you're interested in, but the reactive
component varies quite quickly. You really, really don't want to be tuning
out that reactance at the other end of a length of coax. You might be able
to get away with a few switched inductors or capacitors, and just tune out
the last bit (say, to get from 3:1 down to 1.x:1) at the shack end.
-- The folks at Force 12 have an interesting loading coil for the middle of
their vertical low band dipole that basically stretches and shrinks a big
spacewound coil to tune it. Think in terms of building yourself a coil out
of something like 1/4" copper pipe that's a foot in diameter and a foot
high that can be stretched to 2 feet high. A motor driven lead screw does
the stretching (like in a screwdriver antenna).
The capacitance hat probably won't broaden the bandwidth much, but might
raise the radiation efficiency (in that it increases the average current in
the radiator).
This is mostly about the vertical. My main problem of the moment is
better frequency coverage.
My roughed in plan is some combination of the following:
OTOH, the antenna is clearly "out-hearing" the G5RV, by upwards of 40 dB
in at least one case. I am now hearing zone 15 (Croatia), if faintly, on
SSB and I expect I could probably work a lot of Europe, even as I have it,
with 100 watts on CW. But, is there something else I have overlooked to
improve the DX radiation angle? I laid out the 60 verticals assuming a
velocity factor of 50 per cent as per ON4UN's book. Did I misread that?
Should it have been longer wire or something?
Wires laying on the ground (or buried in it) aren't really something you
can "tune" for resonance (at least not without knowing a whole lot more
about the EM properties of your soil than you're likely to know). They
basically provide a low impedance return for the "image" of your vertical,
and the length is totally non-critical. (to a very rough first order, the
propagation speed in the buried wire is 1/sqrt(epsilon), but I doubt you
know epsilon with an accuracy of better than 50%, and that would really
only apply to a wire that is immersed many skin depths (in the soil), which
yours are probably not)
The basic guideline is that more is better, and that having wires closer
together than 1/100th of a wavelength (or 1/50th, or other numbers in that
vicinity) isn't worth it.
The recommendation of 120 radials 1/2 wavelength long, etc., are really
holdovers from the broadcast industry, as well as measurements and analysis
by George Brown back in the 30s. The goal there is to produce a particular
measured field strength with a certain licensed radiated power, so as to
conform to the terms of your broadcast license grant.
Jim, W6RMK
