1270.1
              ***  TNC 2 - MFJ 1270 - and some Clones  ***
                        Tone Calibration Procedure

     Have you ever wondered to yourself whether or not the Packet TNC you
are using may or may not be generating correct mark and space tones in
reference to the proper frequency?  As the owner of 5 MFJ 1270/1274 TNCs, 
the above question came to mind.  I am not equipped to make adjustments 
on these TNCs with the use of various testing devices, and turned to the 
MFJ Owners Manual for a possible remedy.  They tell you in the Manual 
how to adjust the tones if you desire HF operation (300 Bps) using their
1270B, or 1274 Model, but when trying to find out how to check for
proper calibration on the VHF/220 Mhz/UHF (1200 Baud) -- it's not there.

The TNC 2 has a couple of GREAT features built in to its software.
CALSET and CAL are in the list of Parms, but not explained in detail
that would enable the average packeteer to do his own calibration.

1. 1200 Hz.      -    MARK TONE    (Low tone )
2. 2200 Hz.      -    SPACE TONE   (High tone)
3. 1685 Hz.      -    CENTER TONE (Demodulator)

On the CENTER FREQUENCY tone, it states in the TNC 2 Manual that
1700 Hz is ideal. Continued experimentation has shown that 1685 Hz is
best.  If you are experiencing alot of retries, and having
a difficult time with connects, chances are that your TNC is not
generating compatible Mark and Space tones.

To calibrate the 1200 Baud tones on your TNC 2 or Clone. Follow these
instructions:

1.  Remove the cover of your TNC.  Make sure the HF/VHF button is in the 
    "VHF" position!
2.  Get a screw driver small enough to adjust the trim pots R-76 through
    R-79 located toward the rear center of the TNC circuit board.
3.  Boot up your computer, and enter Command Mode (CMD:) on your TNC.
4.  Try to listen on another Transciever, possibly a Hand Held Radio or
    monitor of some kind, and pick a clean freq. (simplex) with LOW pwr.
    This is helpful, but not required.
continued in 1270.2