Bulletin:   KA3954
Vendor:     Kantronics
Subject:    KPC-9612 connectd to Motorola Mitrek


     TRANSMIT: Pin 4 of the transmitter channel elements is the audio input
     for  modulation.  Some have cut this line loose and applied modulation
     directly  to the  line.  This  is not advisable.   Pin 4  is biased at
     approximately  1.464 VDC.   The bias is necessary  for linearity.  The
     input  audio voltage can not exceed this DC bias.  The Kantronics KPC-
     9612 two output ports are 600 ohm ports and can put out a maximum of 4
     volts  p-p.  This is more then ample  for 3 to 3.5 KHz deviation.  One
     end  of R514  (10 ohms),  in the  transmit audio  amplifier, should be
     disconnected  from the circuit board as this amplifier isn't required.
     A  resistance voltage divider  needs to be  installed that will supply
     the  approximate 1.5 VDC bias  to the modulation line  at pin 4 of the
     transmitter  channel elements.  Connect an 82,000 ohm and a 15,000 ohm
     resistor  in  series.   Connect the  82,000  ohm end  to the  +9.5 VDC
     regulated line and the 15,000 ohm end to ground.  An additional filter
     cap  from the junction of  the 82K resistor and  the +9.5 volt line to
     ground  MAY be required for hum reduction.  Disconnect the line in the
     Mitrek  transmitter section that currently  connects the pin 4 crystal
     line  to R513  and R515  in the emitter  of Q504.   Connect  the pin 4
     crystal  line to the junction of  the 82,000 and 15,000 ohm resistors.
     This  will be  the new  audio input point  with an  input impedance of
     approximately  12,000 ohms.  Be aware that  this point is "hot" with a
     DC voltage.  Port 1 (1200 baud) in the KPC-9612 is AC coupled.  DO NOT
     DC  COUPLE PORT 2 (9600 baud)!  Be  sure that jumper J6 in the 9612 is
     on  one pin only.  Other TNCs may  need to be AC coupled to this line.
     Connect  a 470 ohm resistor and a .15 Mfd cap in parallel.  Place this
     combination  within the DB-9  connector that mates with  port 1 of the
     KPC-9612.   Connect  it in  series with  the lead  that would normally
     connect to pin #1 - this is for pre-emphasis.

     RECEIVE:  The detected  audio output  line to  the volume  and squelch
     controls  has a level of approximately 640 millivolts RMS.  This level
     can  be  increased slightly  by  changing R231  to  2,200 ohms.   High
     frequency roll-off occurs too low in frequency for 9600 baud operation
     so  remove C240 and C451.   Place a 6,800  ohm resistor in series with
     the  line that would normally go to  pin #5 in the DB-9 connector that
     mates  with port  1 on the  9612 -  place it inside  of the connector.
     This  resistor, plus  the input capacity  of port  1, will approximate
     proper  de-emphasis.  Place  a 10,000 ohm resistor  in series with the
     line  that would go to  pin #2 in the  DB-15 connector that mates with
     port  2.  The input capacity of port  #2 is quite low and the resistor
     merely provides some isolation.

     Radiation  from the  transmit and  receive crystal  oscillators can be
     reduced  by soldering a .1 Mfd ceramic cap between pins 1 and 3 of the
     transmit  channel  element  socket  and  the  receive  channel element