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MFJ-1278B MULTI-MODE APPENDIX B MODEM CALIBRATION
Detailed CW Demodulator Alignment Procedure
1. Determine the required Fc for the demodulator. If the radio has a narrow filter for CW,
one of the 2 methods presented on Pages 19 and 20 in the appendix of this manual
should be used to determine the filter center frequency. This frequency should be used
for Fc. If the radio has no narrow CW filter, use the CW carrier offset frequency of the
radio. This information should be available in the your radio manuals.
2. Set the modulator tone to the required Fc using the following procedure.
a. Command the MFJ-1278B into MCW mode by typing "MODE MC <CR>".
b. Install push on jumper at JMP4. This is the watchdog timer defeat jumper.
c. Place a push on jumper at JMP 9, pins 1 and 2. This connects the modulator square
wave output to the SIO chip so that the CPU can measure the tone frequency for
you.
d. Install a push jumper at JMP16 pins 1 and 2 and pins 3 and 4. The two jumpers
when installed correctly will be positioned from side-to-side, with the leds on the
MFJ-1278 facing you.
e. Type "CALSET n <CR>". Where n is a number determined by:
n = INT [ 525000 / F(low) ] + 1
This tells the CPU what tone frequency you are trying to achieve.
f. Command the MFJ-1278B into calibrate mode by typing "CAL <CR>".
g. Command the MFJ-1278B to key the modem by typing "K".
h. Select the MCW tone by pressing the space bar until a voltmeter connected to U16,
pin 9 reads + 5 volts. This signal is more conveniently available at the collector of
Q12.
i. Adjust R139 carefully until both the "CON" and "STA" LEDs on the front panel of
the MFJ-1278B are lit.
j. Remove the jumper placed at JMP 9 pins 1 and 2, and install at pins 2 and 3
k.
Return the MFJ
-
1278B to command mode by typing "Q".