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Chapter 9 AMTOR Operation
1. Put your HF receiver in either LSB or FSK/RTTY/PACKET mode, depending on your set-up.
2. Turn any IF-shift and passband-tuning controls to their center or “off” position.
3. Adjust the volume to a comfortable listening level.
4. Tune your receiver between 14.065 and 14.085 MHz (or elsewhere where there’s AMTOR activity) and
listen for the chirp chirp of ARQ, or the steady data of, FEC stations.
5. When you find a station, use the
THRESHLD
command to adjust the threshold so that the DCD light
glows when a tuned AMTOR station is being received, but goes out when no signal is received.
Alternatively, you can use the
AUTOTHR
(automatic threshold) command to have the DSP-232
automatically adjust the threshold for you.
6. When in the AMTOR Standby mode (as you’re in now), you won’t be able to decode the chirping ARQ
signals. To do so, you need to be in the AMTOR Listen ( ALIST ) mode. Use ALIST to monitor ARQ traffic
flowing between two stations that are linked in an ARQ contact—your DSP will try to synchronize with
whichever of the two stations is the ISS station at the moment. (
ALIST , however, won’t give you error
detection or error correction abilities since you’re not one of the two linked stations.) With poor links, you
might see repeated characters on your screen because the ISS station is repeating blocks of information the
IRS failed to catch the first time they were sent.
If you want to listen in to CQs or on a roundtable QSO where stations aren’t linked (FEC), enter AM .
Again, no error correction will take place.
7. Slowly vary the tuning control on your receiver while glancing at the DSPs turning indicator. Look for the
LED pattern below and adjust the frequency control accordingly.
Frequency too low Tuned in! Frequency too high
Your DSP will not print a block of data if the block contains the same information as the previous block. If the ISS
repeats the same block, you won’t receive it twice unless
you receive an error. If the stations you’re monitoring are
sending error and RQ codes and repeating blocks of characters across their link, you may see some repeated
character blocks. If they’re having link problems, the data on your screen can look very strange indeed, although the
two synchronized stations are enjoying error-free copy.
Note: an alternative way of listening to AMTOR stations is by way of the SIAM mode; see Chapter 11 for
more information.
Going On the Air
Note : Make sure your DSP is adjusted for your SSB transmitter as described in Chapter 3 - Radio
Installation , under the heading SSB Transceiver Final Adjustments . These are critical adjustments. If your
DSPs AFSK level and transmitter’s mike gain aren’t adjusted properly, other stations won’t be able to
copy your signals.
Finally, before you go ahead and transmit, here are some helpful hints:
♦
Don’t use the VOX control—use the PTT line from your DSP.
♦
Turn off the AGC circuit—use the RF gain control to prevent receiver blocking on stronger signals.
♦
Turn off all compression or other audio processing.
♦
If you’re using an AFSK audio input, keep the audio level to the microphone input circuit as low as
possible to avoid overdriving the audio input stages.
♦
Adjust the transmitter’s drive to prevent excessive ALC action; use more effective RF antenna loading to
adjust output power levels.
Before you transmit, however, you have to decide if you’re going to “call CQ” or answer someone’s CQ call.
Calling CQ
When you initiate a CQ call, you must do so in the FEC AMTOR mode.
September, 05 9-3