MFJ-1270C/1274C MANUAL APPENDIX B: CALIBRATION
Page 238
NOTE:
The threshold control on the MFJ-TNC must be set to a position which
will allow the DCD circuit to function properly. A setting approximately 1/3 to
1/2 of the total range starting from maximum CCW should be adequate.
Continue to VERY CAREFULLY adjust R113 until the STA and CON LEDs on
the front panel either change state very slowly (alternate which one is lit) or until
both are simultaneously illuminated.
NOTE:
This is a very critical adjustment. It is very unlikely that you will be able
to cause both LEDs to be turned on simultaneously, for longer than a very brief
instant. Just fine tune R113 very carefully, and notice the action between the
STA and CON leds. If they flash back and forth this is acceptable.
7. Return the MFJ-TNC to command mode by typing a "Q".
This completes demodulator center frequency alignment using the built in
calibration software. If there were any problems in the preceeding procedure,
then DO NOT go beyond this point. If you do the calibration will be inaccurate.
Now that the demodulator and modulator are properly aligned
to one another, the tuning indicator can be set for proper center indication.
Tuning Indicator Alignment
This procedure adjusts the tuning indicator so that it correctly indicates when a
signal is properly tuned in relation to the demodulator center frequency. In order
for the Tuning Indicator to be properly aligned the above calibration must be
done properly, otherwise you will align the Tuning Indicator improperly.
NOTE:
The tuning indicator should ONLY be adjusted in reference to the 300
baud 200 Hz shift modem used for HF packet and RTTY. If adjusted for this
modem, It will indicate with sufficient accuracy for all other modes.
1. If you have not just finished aligning the modem as per the above
instructions, do so now. Otherwise you may be aligning the tuning indicator to
incorrect calibration settings.
2. Install push on jumpers at JMP 4 and JMP 7, if they are not still in place
from the modem alignment procedure.
3. Ensure that the jumpers on JMP9 and JMP16 are placed as stated in the
demodulator alignment section above.
4. Command the calibration routine to send 50 percent duty cycle square
wave data from the modulator by typing "RXCAL" <CR>.
5. While observing the LEDs in the tuning indicator, adjust R212 in the
tuning indicator area so that either the 10th or 11th led from the left (or both) are
illuminated.
8. Return the MFJ-TNC to command mode by typing "Q".
9. Remove jumpers at JMP 4 and JMP 7.
This completes the tuning indicator alignment.
Now the modulator, demodulator, and tuning indicator are all aligned to the
same center frequency. If you notice that on the air reports suggest that you are
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