Note
The Micoder microphone has its origins in the HW-2021 (delivered the previous year) as an optional auto-patch encoder.
The HD-1982 was designed with what quickly became outdated technology. The tone encoder used two separate tone generators built from a transistor and three integrated circuits. In the newer HD-1984, the entire tone generator circuit was built into a single integrated circuit.
The HD-1982 can be used with any radio requiring a high impedance microphone, and can be assembled with or without a hanger button. Requires a frequency counter for calibration.
Note: The side of the microphone opposite the keypad can be fitted with a decorative nameplate or a hanger button. If the hanger button is present, there is no outward way to distinguish the HD-1982 “Micoder” from the HD-1984 “Micoder II.”
A modification was later offered which upgraded the HD-1982 to the HD-1984. The upgrade involved replacing the old encoder circuit board with a new one.
References:
Review. QST. Nov 1976, p. 37.
Encoder IC for. QST. Jan 1978, p. 39.
“Mycoder” better design. QST. Apr 1978, p. 27.
Low impedance operation. Ham Radio. May 1978, p. 86.
Low impedance operation (more). Ham Radio. Sep 1978, p. 8
Improvements. Ham Radio. Nov 1978, p. 42.
Replace battery for better audio quality. QST. Apr 1979, p. 44.
Microphone type: electret condenser.
Output level: 30 mV RMS maximum.
Frequency response: 300 to 3000 Hz.
Output load: 10kΩ minimum.
Encoder frequency tolerance: 1.5%.
Distortion: less than 5% (harmonic plus intermodulation)
Operating temperature range: –20 F to +110 F
Battery life: about 6 months.
Power requirements: one 9-volt battery (NEDA 1604), 12 mA.
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
