***  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.
5.  Enter this command from command mode:
    CALSET 438        or       (n=525,000 / 1200 + 1) 
    which in either case will equate to 438 or therabouts. 
    This is your MARK tone CALSET number or 1200 Hz tone.
6.  Remove the jumper from JMP 8 and place on JMP 9 Pins 1 and 6.
    (If you are facing your TNC pins 1 and 6 are on the far right).
7.  Type CALIBRA or CAL. Hit the letter "K" and then the space key to
    get the lower of the two tones.
    NOTE: you may want to remove the jumper from JMP 5 to use on JMP4
         to override the watchdog timer circuit.
8.  Adjust R-78 until the you hear a change in pitch of the transmitted
    tone, AND both the CON and STA led's light up and stay lit, or at
    least alternate back and forth the same rate. Ideally, they should
    both stay lit simultaneously.
9.  Hit the "K" again, and then "Q" (to quit calibration) and then go
    back to CMD: mode.
10. Give the TNC the command:
    CALSET 239        or      (n= 525,000 / 2200 + 1)
    which equals a CALSET number of 239.
11. Repeat step 7.  Repeat step 8, but adjust R-77.  Repeat
    step 9.
12. NEXT - REMOVE the jumper from JMP 9 (Pins 1 and 6) and place the
           jumper on Pins 2 and 5. - the center two pins of JMP9.
13. Go to CMD: mode and type this:    "CALSET 157"        or
    (n= 262,500 / 1685 + 1) which would equate to a CALSET number of
    157.  This is your Demodulator/or center freq of 1685 Hz.
14. Repeat step 7, this time adjusting R-79 for the
    best condition of the CON and STA LEDs (both lit at same time).
15. Replace JMP 8 (from JMP9) and replace JMP 5 (from JMP4).

Once you have done all of the above, you have successfully calibrated
the TNC's tones.  LAST BUT NOT LEAST...follow the MFJ or TNC 2 Manual 
on how to properly set the deviation level adjustment (R-76) so that your 
transmitter puts out in the neighborhood of 2.8 to 3.0 kHz of deviation.