MFJ MFJ-1270C, Системное руководство

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MFJ-1270C/1274C MANUAL BASIC OPERATION
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continuous frames of long data length. For HF operation at 300 baud, we recom-
mend setting
MAXFRAME to 1.
The MFJ TNC detects a busy channel by monitoring the lock- detect signal from
the demodulator. The presence of a lock- detect signal is indicated by the Data
Carrier Detect (DCD) LED. Each time DCD goes off the MFJ TNC will start a
DWAIT interval which must elapse before the channel is considered to be
available. On a noisy channel spurious lock-detect signals may be generated.
For HF and OSCAR operation you should set
DWAIT to 0. The random wait
before retry transmissions can be disabled by setting TXDELAY
0
and using AXDELAY to set the required keyup delay. Of course, AXHANG
should be 0 for this application.
If you are operating a full-duplex radio station (simultaneous transmit and
receive) such as an OSCAR 10 station, you should set
FULLDUP ON. The
MFJ TNC is always electrically capable of full duplex operation, but this
parameter causes the protocol to behave differently in acknowledging packets. In
addition, the MFJ TNC will ignore the state of the DCD line.
Although intuition tells you that lower baud rates will reduce the number of
packet retries, there is usually a small range between "too fast" and "too slow."
A slower packet takes longer to transmit and is therefore a larger target for fades
and static crashes. The entire packet must be received correctly in order to be
accepted. Data rates of 1200 baud have been used on both HF and through
OSCAR 10.
HF activity may generally be found on 7.093 or 14.107 MHz. Use LSB or USB
- it really doesn't matter (although most stations use LSB when referring to the
suppressed carrier frequency).
Tune through a few packet signals. Tune slowly! You will find a point at
which the display becomes bright. As you continue tuning, you will see the
moving bar display slide across your tuning indicator. When one of the center
LEDs is illuminated, you are tuned in and you should be able to copy the
packets.
Each bar on the tuning indicator represents about 10 Hz. Thus, if a packet
comes through and you are 4 bars off, re- tune your transceiver 40 Hz in the
indicated direction. The direction depends on the sideband you selected and the
manner in which you have the tuning indicator oriented. One or two tries will