Mopdifica ICOM R71A per copertura fino a 0,0 kHz:

[RADIOMOD]

        TRICKING THE ICOM R71A TO TUNE BELOW 100 KHZ


     The ICOM R71A general coverage receiver is designed for
     VLF reception down to about 97 kHz.

     The following steps will  confuse  the  microprocessor-
     based  controller sufficiently to permit reception down
     to 0.0 kHz:

       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
           simultaneously rocking the MEMORY-CH rotary  con-
           trol  to  switch  back and forth between a memory
           channel with a frequency in it and a clear memory
           channel.

           Continue rocking both the controls until  a  fre-
           quency of 0.000.0 appears on the digital display.

       4.  Depress the WRITE button.  This stores the  0.000
           MHz frequency in a memory channel.

           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 counterclockwise, the radio will immediately
           revert to 29.999 MHz.

     To tune below 100 kHz in the future,  just  recall  the
     0.000 MHz frequency from the memory channel and use the
     tuning knob to tune upward.  That way, you  don't  have
     to  use  two  hands  every  time you tune to a VLF fre-
     quency.

     I used a Wavetek 180 sweep/function generator to verify
     that  the R71A is indeed receptive to signals below 100
     kHz.