USING THE ICOM-2E AS A TRANSCEIVER FOR PACKET RADIO
        ---------------------------------------------------

The ICOM-2E handheld is equipped with 2 connectors for use of an external
microphone/speaker (type HM9).
These connectors can also be used for packet radio. Either a special plug
(with both a thick - 3 mm - and a thin - 2 mm - plug) is necessary, or 2
separate "earphone" jacks of respectively 3mm and 2 mm thickness.

As shown in the schematic diagram below, the "tip" of the 3 mm jack is
connected with AF input to the packet TNC, whereas the "tip" of the 2 mm
jack carries (via a relay-contact) the AFSK output of the TNC.

Just as in the HM9-microphone/speaker, both a small capacitor (470 pF) and
a resistor (33 k) have to be put between the audio (AFSK) line and the
ground. The relay contact replaces the HM9's PTT contact.

AF from receiver to TNC

0--------------------------------------------------------|
                                                   ------|-\
 Ground                                      ------|-o  |o  | plug 3 mm
0--------------------------------------------|     --------/
       |            |                        |
       |           ---                       |
      ---470pF     | |33k                    |     --------\
      ---          | |                       ------|-o  |o  | plug 2 mm
       |           ---                             ------|-/
       |            |                       /            |
0------------------------------------------/  -----------|

  AFSK from TNC to transmitter            relay contact


 PTT ------        ------
0----|    |--------|    |-------------> +12V
     ------   |    ------     |
     10k      |    22 k       |
              |            ----
              |           /emitter
              |         |/
              ----------|   BC557
                        |\
                    coll.  \------------
                           |          |
                       ---------     ---
                       |relay  |     / \
                       ---------     ---
                           |          |
                           -----------------> ground

Hans PA3ESZ @ PA3EAE

(Downloaded from GB7SYP)