Audiovox MS-407 Owner's Manual page 6

AM ANTENNA TRIMMER ADJUSTMENT
The antenna trimmer can be reached through the small hole inside the cassette door (See
diagram below) Tune radio to a weak station between 1200 and 1400 KHz AM. (If you cannot
find a weak station in this range, tune to any strong station, and adjust tuning slightly off station).
Adjust antenna trimmer for maximum output.
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