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SGC Inc. SGC Building, 13737 S.E. 26th St. Bellevue, WA 98005 USA
P.O. Box 3526, 98009 Fax: 425-746-6384 Tel: 425- 746-6310 or 1-800-259 7331
E-mail: [email protected] Web site: http://www.sgcworld.com
© 1998 SGC Inc
SG-235 Manual
money by expecting the fiberglass hull to act as an insulator and not using a
lower insulator. The hull is not a good insulator and a thin layer of wet salt
water will degrade the ground further. Similarly, mobile HF users who rely on
a poor quality ballmount find these are especially prone to arc over inside the
ball mount where it is difficult to detect.
The point we are making here is simply this: you should have a leakage path
of 2 inches at all points on your antenna and especially in the area of the feed
point: 10,000 to 30,000 volts of RF energy will not be adequately confined by
inexpensive insulators.
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Some vexing problems don't relate directly to the antenna or the ground sys-
tem but may nonetheless cause difficulties.
Here are two of the most common types:
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n .. The transmitter may have a tendency to oscillate. The general
symptom is that the coupler will work well with another radio but will not
tune correctly when the desired radio is in place. The coupler finds a tuning
solution, as indicated by the remote tune indicator going on, but then resumes
hunting. In a majority of cases this will be caused by an overly sensitive
transmitter final amplifier section or by inadequate shielding around the
amplifier.
We know of several radios that oscillate relatively easier than most radios
because they are housed in a plastic case. A plastic case does not provide an
adequate shield for serious RF components. In some of these cases, putting
grounded foil around the radio, or changing the radio location and orienta-
tion, has changed the symptoms. But if you want quality performance, select a
solid radio.
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y .. Power supplies have been known to cause problems for HF
users because they change voltage when the load on them changes. If the
transmitter is drawing heavy current, as transmitters do when they are run-
ning at peak input power, the voltage to the antenna coupler may change
enough to cause the coupler to either drop into a reset mode (under +11 VDC
being present) or, the transmitter final amplifier impedance may change
greatly, thus changing the tuning solution.
To alleviate this condition, remember to use a power supply which has both
adequate current handling capacity and good dynamic regulation. Better yet,
use a regulated power supply of an adequate rating.