Note
Ham Radio, Aug 1970, p. 84.
Ham Radio, Sep 1970, p. 81.
Ham Radio, Aug 1971, p. 66.
The FM-6 digital frequency meter measures and displays the frequency of any transmitter carrier operating up to 35 MHz automatically and
continuously.
Connection i s made with a coax T connector and a special cable to any transmitter, transceiver, or exciter with an output from 1 to 600 watts. For higher power transmitters, the unit is inserted between the exciter and the final amplifier.
The heart of the FM-6 i s a 100-kHz crystal oscillator, adjustable to WWV, that produces a precise gate to permit the unknown signal to pass to a digital counter and display. To increase accuracy and prevent ambiguous readings, a special dual synchronizer circuit is used to synchronize the gate with the signal to be measured.
The readout consists of two longlife Nixie tubes that display both kilohertz
and megahertz together with the appropriate decimal point. As an example, if the frequency is between 7248 and 7249 kHz, the display will read 7.2 on the MHz scale, and 49. on the kHz scale. On higher frequencies, the highest digit is deleted. (ie. 14.3 MHz would read 4.3). The readout is constant as long as a carrier is on the air.
Once every second a sample of the transmitter signal i s made, and the frequency reading is "updated." This process takes only a few microseconds and the reading is stable and constant between measurements.
Measurement accuracy is within 100 to 200 Hz, and the readout accuracy is 1 kHz. The unit is all solid-state and uses TTL-MSI (medium scale integration) logic. A high-voltage power supply for the tubes, and a regulated supply for the logic circuits is self-contained in the small metal enclosure.
Replaced by the FM-36 three-digit version in October 1971.
Kit, $139.95
Assembled. $169.50
References
Brief description. Ham Radio, Oct 1970, p. 78.