parnass@ihu1h.UUCP (Bob Parnass, AJ9S) (02/12/85)
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Tricking the ICOM R71A to Tune Below 100 kHz
Bob Parnass, AJ9S
The ICOM R71A general coverage receiver is designed for VLF
reception down to about 0.097 MHz.
The following steps will confuse the microprocessor-based
controller sufficiently to permit reception down to 0.0 MHz:
1. If all 32 memory channels contain frequencies, use the
FUNC and CLEAR buttons to clear a memory channel.
2. Place VFO/M switch into the M (Memory) position.
3. Using all the manual dexterity you can muster, rock
the Main Tuning knob back and forth, while simul-
taneously rocking the MEMORY-CH rotary control to
switch back and forth between a memory channel with a
frequency in it and a clear memory channel.
4. While manipulating both the controls described in the
previous step, a frequency of 0.000.0 will appear on
the digital display.
You can now rotate the Main Tuning knob clockwise to
tune up from 0.000 MHz to the frequency you want. Be
careful: if you rotate the Main Tuning knob counter-
clockwise, the radio will immediately revert to 29.999
MHz.
I used a Wavetek 180 sweep/function generator to verify that
the R71A is indeed receptive to signals below 100 kHz. To
make things easier, store the 0.000 MHz frequency in a
memory channel for future use. That way, you don't have to
use two hands every time you tune below 100 kHz.
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Bob Parnass, Bell Telephone Laboratories - ihnp4!ihu1h!parnass - (312)979-5414