MFJ MFJ-1270C, Системное руководство

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MFJ-1270C/1274C MANUAL ADVANCED OPERATION
Page 101
3. Make sure the MFJ TNC is in HF Packet mode and that the HF Packet
modem has been selected.
4. Set the audio output level so that the tuning indicator is responding to the
background noise coming through the filter. This can be verified by observing
whether or not the tuning indicator "follows" the noise as the IF shift control is
rotated.
5. Tune to a frequency which has ABSOLUTELY NO signals in the
passband. It is very important that only noise is coming through the filter. If
you have access to a RX noise bridge, an alternative is to use the bridge as a
noise source for the receiver. No antenna is required in this case.
6. Adjust the IF shift control on the radio so that the tuning indicator on the
MFJ TNC is centered in its display area.
7. Adjust the audio output of your radio to TNC so that the DCD LED is
flickering with false DCD indications. Make the adjustment so that the DCD
duty cycle is more than 10 but less than 50 percent.
8.
Carefully adjust the IF shift control on the radio to produce maximum DCD
activity. This is the optimum point for the filter center frequency. Note the
position of the IF shift control for future reference. This is the position you will
want to use for all of the narrowband FSK modes.
If your radio has no provision for IF shift, you will have to determine the
center frequency of the audio which is passed through the filter and realign
the modem to the center frequency of the filtered audio. If you are lucky, this
may turn out not to be necessary. The tuning indicator and DCD LED can be
used to give you an indication when the modem is aligned with the filter similar
to the indications described above. If the tuning indicator hovers around the
center of the display when the modem is listening to noise being passed
through the narrow filter as described above, realignment of the modem is
unnecessary.
If you have determined that it is necessary to realign the modem center
frequency to the radio filter center frequency, You should refer to
Appendix D
at the end of this instruction manual for the alignment procedure.
HF Packet Operation