Steve,
You still haven't determined an important piece of information - At what
frequency is the current antenna resonant (X = j0) ? Find someone with a
Palomar
Noise Bridge, and the knowledge to use it correctly. Take them and a receiver
out to the tower.
I know the TowerTalk purists will start screaming about the inaccuracy of the
Palomar Noise Bridge, but I have found it to be an extremely useful tool in
RF-noisy environments where an antenna analyzer cannot be used.
And, BTW, tell us about the guy wires and how they are broken up.
73,
Steve, N2IC
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There seems to be a bit of confusion as to the tower height and the
tower insulator location. It's probably in the way I explained it in the
first post. Sorry about that.
A. Starting at ground level is the concrete base.
B. Out of the concrete base is a piece of Rohn 25G, upside down,
sticking up 4 ft.-3 inches above the concrete. (At approximately 6
inches above the concrete is the ground radial buss bar bolted directly
to two tower legs.)
C. Next is the insulator(s) and they are 4 inches in height. The
insulators are made of high density (LGQ) fiberglass rod.
D. Stacked on top of the insulators is 120 ft.-6 inches of tower. The
top section is a Rohn "flat top" with a 2" bearing. The bearing was
included to accommodate the addition of a stinger if we needed it.
E. The guys are broken with the standard 5.5 inch (ANSI 54-3) porcelain
insulators.
Almost all matching was attempted directly at the tower feed point. This
consisted of a 15 inch RG8 pigtail, PL259 on one end and split at the
opposite end for 5 inches. The center conductor attached to the tower
just above the insulator, with the shield attaching to the base section
just below the insulator. All the ground radials come to a common
aluminum buss bar securely attached to the bottom base section 6" above
the concrete.
The equipment used for trying to obtain a reasonable match are as follows;
- RF signal source: MFJ 249, MFJ 259B and a CW exciter with variable rf
output, 0 to 30 watts, 1.00 MHz to 4.50 MHz.
- VSWR measurement: The two MFJ analyzers. Two Bird meters, one meter
with 50w slug (fwd) and the second with 5 watt slug. (rev) and finally a
Yaesu YS-60 pwr/swr meter.
Only once, did I try loading the vertical from the shack. I used a
75ft. piece of Andrew LDF4 heliax and my Yaesu. Poor results... the swr
foldback killed the output.
The matches tried are;
Low pass "L"... series inductor 0 to 32uh with 25 to 1000pF capacitor
shunt to ground.
High pass "L"... series cap 250 to 1800pF with above inductor shunt to
ground.
High pass "T"... series 72 to1200pF cap, same variable inductor to
ground, and then another 75 to1200pF cap.
Low pass "Pi"... series variable inductor with two caps on either side,
both are 572 to 1700pF.
?? ... series cap 72 to 1200pF
?? ... variable inductor, one end to ground, the other
end to tower with RF in on the variable tap.
?? ... variable inductor, one end to tower, the other
end floating, RF in on variable tap.
?? ... parallel inductor and 72 to 1200pF cap, in
series with center conductor.
All variations of the above mentioned schemes have failed in one way or
another. The ones that did marginally work have too high of a Q and are
extremely narrow in band width.
As an absolute last ditch effort, I can use a Palstar AT4K antenna
tuner. I personally don't like to use tuners and would much rather use a
resonant antenna. A tuner is just a 'cheat' and one more thing that can
fail at the most inopportune time. Nuf said abt tuners!
Well, that is our version of the "old collage try" and we seem to have
failed somewhat. Maybe it's time to put back up the inverted L's and dipole.
Best regards and 73,
Steve AB5MM
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