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Old November 13th 06, 08:26 PM posted to rec.radio.amateur.antenna
Norm VE3CZI Norm VE3CZI is offline
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First recorded activity by RadioBanter: Jun 2006
Posts: 114
Default HOW do "dual-band"VHF/UHF antennas work?

I had a problem with an recently purchased USED Diamond SG-7500 at a Flea
Market.
Was told it was OK, but upon testing on the Vehicle I had very poor
VSWR....So much for Flea Market Bargains! !
I tested it with an MFJ Antenna Analyzer which showed it to be "out" but was
not sure whether it was the base matching unit, or the phasing elements in
the antenna rod.
I emailed Diamond and received a very nice letter with the construction of
the antenna and prices for the replacement parts. Did not solve my problem,
but "did" lead me down the right path.
I ended up borrowing a friend's SG-7500. Measured the Capacitive &
Inductive elements in the Antenna Rod..no difference. Since the base
utilizes a capacitor in series AND a coil shunt to ground, it was awkward to
evalualuate if the shunt coil or capacitor in the Base Unit was bad. I
substituted and base unit on my antenna...voila! Good Match. I ordered up
a new coil from Mfr for $35.00 and problem solved.
Substitution is sometimes the best troubleshooting technique. I suspect the
original owner put TOO much power into the Base Unit !!

73...Norm VE3CZI


"Paladin" wrote in message
ps.com...
Hello "Antenna-Lovers",
How do dual-band antennas work? I bought a COMET
"SSB-7" antenna for my mobile radio. It worked great for a year or more
and then,trouble. I don't know "HOW" to trouble-shoot it.
Where on the antenna can I check for "continuity" or somewhere I can
look to find a "fault" of sorts.
It costs a bit more than a lower gain antenna. How can I trouble-shoot
it ?

73's Paladin