I had the same annoying problem when troubleshooting my 160M phased
vertical array. Using the MFJ259, neither vertical seemed to have a
j=0 point anywhere near the 160M band, and the readings jumped around
a bit. I concluded that it was AM BC interference. There is a local
station on 1490 a few miles away across salt water, with both analog
and digital signals, and the transmitter is apparently not adjusted
well for the digital, since the signal is very wide.
I tried the MFJ filter and was not successful (if anyone wants to buy
it, contact me off list).
I was able to borrow a vintage General Radio RF impedance bridge from
a local guy, and it worked great. I used my MFJ259 as the signal
source and IC706 as the detector. I could tune the box to drop the
detected signal from pinning the meter to nearly inaudible and read
the R and X to within an ohm easily. Got both verticals to resonate at
1830 (originally one was at 1800, one at 1920 or so). Turned out that
one was about 30 ohms, and one was about 60, which puzzled me.
Numerous experiments using the GR box to corroborate models led me to
figure out that my tower was coupling significantly to the "60-ohm"
element, and I was able to eliminate that problem.
I later found a GR box for sale and bought it.
I suppose one of the newer fancy VNA boxes would also work after
calibration for any filters inserted, but I like old stuff and don't
mind a little calculator or Excel work. I tried unsuccessfully to
persuade a couple of manufacturers to make an updated (lighter,
smaller) version of the GR box.
73,
Doug K1DG
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Topband reflector - topband@contesting.com
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