Some TS-120S users may complain of a hum during SSB operation, which may be caused by RF feedback. There may be various reasons for this complaint.
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Bad feedline and antenna system ground.
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Poor Mic hookup or shielding.
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Vertical antenna with poor or no radial system.
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For base operation with other than a PS-30 Power supply:
Poor regulation and insufficient filtering in the supply.
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Linear amplifier creating hi RF field near the operating position.
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RF induced back into the power supply causing falsie protection (other
than PS-30).
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RF pickup by any cables to or from ancillary equipment.
Prevention is the best cure. For those cases where all normal measures
have been tried, try installing a .01uF bypass cap across the mic input
jack between pins 1 and 4.
Some AFSK operators may have similar RF feedback problems with TS-820S or
TS-520S. Bypass the mic ground pin to the chassis, pin 3 to 4 and in
extreme cases, install a ferrite bead on the Mic coax center conductor at
the microphone connector.
Please annotate your service manual.
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