ICOM IC-970
                         MODEM INTERFACES
                   FOR SATELLITE COMMUNICATIONS
 
 
     DO NOT USE THE IC-970 MICROPHONE CONNECTOR FOR TRANSMIT OR
RECEIVE AUDIO.  There seems to be too much audio shaping in this
path.  Use the DATA connector on the back of the IC-970.  I have
tried it both ways without much luck through the microphone
connector.  The DATA connector method works very well.
 
PAC-COMM PSK-1 MODEM - 
 
1.  IC-970 INTERFACE -  The IC-970 DATA connector leads to be used
are as follows (see page 13 of owner's manual):
 
     a. Pin 1 is transmit audio from the PSK-1 VHF RADIO connector
        pin 1 to IC-970.
     b. Pin 7 is the push to talk lead from the PSK-1 VHF RADIO 
        connector pin 3.
     c. Pin 8 is the UP/DOWN lead from the modem to the IC-970.
        This lead is connected to the PSK-1 UHF RADIO connector
        pin 1. Install a 470 ohm resistor from pin 1 to pin 5 of 
        the PSK-1 UHF RADIO connector.
     d. Pin 9 is a ground lead to the PSK-1 VHF RADIO connector 
        pin 2.
     e. Pin 10 is the SUB band audio output from the IC-970 to the
        PSK-1 VHF RADIO connector pin 4. SEE NOTE 1.
 
 
2.  Set the PSK-1 parameter configuration as follows:
 
     MODE  -  SATellite
     MODEM -  IN (in line)
     JT/SP -  JOINT (for IC-970)
     AFC   -  USB or LSB (same as the mode selected on the IC-970)
     KC TUNER RADIO TYPE - NONE (not used at this station)
     RS232 SPEED - (RS232 port not used at this station)
     DCD SENSE   -  Use default except for KANTRONICS TNC. 
                    Doesn't seem to make a difference in Full
                    Duplex mode).
     MAXIMUM STEP RATE - 12 steps per second
     MIC-CLICK SENSE - ACTIVE LOW (for IC-970)
     CLICKS-PER-STEP - 1
 
     The PSK-1 allows about 150 to 200 hertz drift before
frequency correction pulses begin. In the IC-970 in SSB mode, each
pulse results in a 10 hz frequency change. Ten such pulses occur
for each change in the IC-970 frequency readout.  The above
arrangement will track an overhead satellite pass with maximum
Doppler shift.
 
 
 
TAPR PSK MODEM -
 
1.  IC-970 INTERFACE -   The IC-970 DATA connector leads to be
used are as follows (see page 13 of owner's manual):
 
     a. Pin 1 is transmit audio from the modem VHF RADIO connector
        pin 1 to IC-970.
     b. Pin 7 is the push to talk lead from the modem VHF RADIO 
        connector pin 3.
     c. Pin 8 is the UP/DOWN lead from the modem to the IC-970.
        This lead is connected to the modem UHF RADIO connector
        pin 5.
     d. Pin 9 is a ground lead to the modem VHF RADIO connector 
        pin 2.
     e. Pin 10 is the SUB band audio output from the IC-970 to the
        modem VHF RADIO connector pin 4. SEE NOTE 1.
 
2.  Construct the following on a 12 pin header strip socket and
install it on the combination JP5/JP6 plug in the modem:
 
 
                     TOP VIEW OF CIRCUIT BOARD
 
                            *       *                   |
                            |                           |
                            *       *----,              |  JP5
                                    |    |              |
                            *       *    \              |
                                         /   470 ohms
                            *-------*    \              |
         To          1k ohms             |              |
    2N2222 Base ----\/\/\---*   ,---*----'              |  JP6
                                |                       |
                        ,---*   |   *                   |
                        |       |
                        |       To 2N2222 Collector
                        |
                        | To 2N2222 Emitter
 
 
     The TAPR PSK modem allows about 30 to 40 hertz drift before
frequency correction pulses begin. In the IC-970 in SSB mode, each
pulse results in a 10 hz frequency change. Ten such pulses occur
for each change in the IC-970 frequency readout.  The above
arrangement will track an overhead satellite pass with maximum
Doppler shift.
 
 
 
     NOTE 1: The IC-970 DATA connector pin 10 only carries SUB
band audio. In order to use your TNC for simplex (MAIN band)
terrestrial packet communications you must obtain Main band audio
from IC-970 DATA connector pin 5. This will require you to provide
a means of switching the modem (PSK-1 or TAPR) VHF RADIO connector
pin 4 to either IC-970 DATA pin 10 or DATA pin 5 for SUB band or
MAIN band audio respectively.
 
     NOTE 2:  The IC-970 has an internal switch (see pages 13 & 42
in your owner's manual) which lets you set this input for 100 mv
(default) or 3 mv. Placing a jumper on JP5 in the PSK-1 or JP7 in
the TAPR PSK modem significantly increases the level of transmit
audio from the modem which can then be adjusted with R40 on the
rear panel of the PSK-1 or R6 in the TAPR modem. You should leave
the IC-970 in the 100 mv input position in this case.
 
73, W0SL