MFJ MFJ-1270C, Системное руководство

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MFJ-1270C/1274C MANUAL ADVANCED OPERATION
Page 98
Setting up your Radio interface will follow exactly the same procedure as for
VHF NBFM operation with the exception that you will probably not need to set
the modem output level. This is because linear mode radios typically have a
transmit audio level control on the front panel and an indicator which tells you
when you have set the level correctly. You will adjust the audio level just as you
would for SSB operation.
If you are using the auxiliary audio input connector (other than microphone
input), you MAY need to adjust the transmit audio level from the MFJ TNC
modulator. This is because many auxiliary audio inputs are intended for phone
patch audio. These levels are typically much higher than microphone levels.
If you do adjust the output level of the MFJ TNC to a relatively high value for
this type of application, do not operate the MFJ TNC with a VHF NBFM radio
unless you take steps to assure that the audio level for the FM radio will not
produce excessive deviation. If both radios are to remain connected to the MFJ-
1270C, you can set the audio level for each radio independently by using the
audio output level adjustments, R157, on the left side of the MFJ TNC with a
small screw driver.
The modem center frequency used by the MFJ TNC for all of the narrow shift
AFSK modes including HF packet operation is 2200 Hz (2125 and 2295 Hz
tones). Most frequencies listed for packet operations in the HF bands were
established using a modem center frequency of 1700 Hz (1600 and 1800 Hz
tones) in lower sideband mode. This is a 520 Hz offset (2220-1700) between the
two modem standards. So a listed frequency of 7093, for example, will cause
you to have a frequency display on your radio of 520 Hz PLUS the listed
frequency (IF you are also using lower sideband mode). Thus you should find
the 7093 KHz packet activity centered around 7093.52 KHz.
Your tuning indicator (MFJ-1274C only), when properly centered, is easily
capable of 10 Hz alignment accuracy. It should be used as the tuning reference
on any individual signal regardless of the frequency indicated on the radio dial.
NOTE: The signal actually transmitted by your SSB transceiver ( F(emission) )
when using the MFJ TNC for AFSK HF packet operation using lower
sideband will cover a band of frequencies approximately 400 Hz wide and
centered at the transmitter indicated carrier frequency (F(ind)) minus the modem
center frequency (Fc).
So you would use:
F(emission) = [ F(ind) - Fc ]