74091213
Aug 27, 1990
Aug 6, 1991
amateur radio instrumentation, specifically resistance-reactants (R-X) noise bridges; receiver preamplifiers; antennas; antenna turner; VLF converters; transmitters; loop antennas; antenna baluns; electronic keyers; and standing wave ratio meters; and audio tone control equipment, specifically; tone encoders; tone decoders; digit sequencers; and decoder relay latches
Electrical and Scientific Apparatus