Hal Communications ST-6000, Инструкция по эксплуатации

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4-8
the signal tones and the discriminator filters. If both mark and space tones are not sensed in the
discriminator, the "plus-plus" voltage remains at a low average value and the autostart circuit will
be in the standby condition, giving a continuous mark output. After the autostart has remained in
the standby or mark-hold condition for 20 seconds (nominal), the power to the MOTOR AC socket
on the rear panel is turned off with an internal relay. If valid mark and space tones are now
sensed in the discriminator, the "plus-plus" voltage will increase and activate the autostart after a
delay of either 3.5 seconds (AUTOSTART - SLOW) or 1.5 seconds (AUTOSTART - FAST). The AC
power to the MOTOR connector is now switched on and. the data is allowed to drive the post-au-
tostart data line. Immediately after the tones turn-off at the end of a transmission, the autostart
returns the post-autostart data to mark hold, completing the cycle.
Because of the turn-on delay inherent in the autostart, it is recommended that tuning of the
RTTY signal be done with the AUTOSTART switch in the OFF position during initial testing of the
ST-6000. After the operator has some practice in tuning the receiver, he may then wish to leave
the autostart circuit ON, remembering to account for the time delay of the autostart.
The autostart trigger voltage level on the "plus-plus" line is adjustable with a potentiometer
mounted on the control circuit board inside the ST-6000 cabinet. The potentiometer is located be-
hind and slightly to the left of the KOS front panel switch and is labeled "AUTO" on the circuit
board. Rotation of the screw-drive adjustment CCW decreases the "plus-plus" voltage required to
trigger the autostart, thus INCREASING the autostart SENSITIVITY, Conversely, CW rotation de-
creases the autostart sensitivity. This control is normally set at the factory to trigger the autostart
on all signals giving a tuning meter reading of 0.5 and higher. The user may adjust this control to
fit his own requirements. If the autostart sensitivity is set too close to the noise level, false printing
may occur on noise or interfering signals; if set to too high a level, the autostart may not trigger
on all but the strongest signals with exactly correct shift. Experience will determine the optimum
setting for a particular system. Notice that the "plus-plus" voltage and therefore autostart sensitivi-
ty are directly proportional to the degree of match between the signal tone frequencies and the
center frequencies of the discriminator filters. It may therefore be difficult to set the autostart sen-
sitivity and receiver tuning to respond to signals with improper frequency shift. Also, if the trans-
mitter OR receiver should drift, the signal tones will soon no longer match the discriminator filters,
causing the autostart to "shut-down". If drifting is a problem, the receiver should either be moni-
tored often and manually retuned as required or the autostart should be switched OFF.
4.11 Antispace Circuit
Like the ST-5, the ST-6000 incorporates a timing circuit that prevents the continuous spacing
condition (machine "running-open") in the post-autostart data output if a space tone longer than
approximately 250 ms is received. When a long space condition is detected, the antispace circuit
activates the mark-hold circuitry. A continuous space will NOT turn the motor power off. The anti-
space circuit is always active, but ONLY controls the post-autostart data output. The pre-autostart
data output is NOT controlled by the anti-space, autostart, or standby circuits.
4.12 Tone Keyer Circuit
The ST-6000 includes a crystal-controlled tone keyer that is very similar in design to the previ-
ous HAL model XTK-100 tone keyer board. All mark, space and CW-ID tones are digitally synthe-
sized from high-frequency crystal oscillators. The crystal frequencies are either 2000 or 3000 times
the desired output tone frequency. Unlike previous tone keyers, the ST-6000 CW-ID tone is gener-
ated at 100 Hz BELOW the mark tone instead of above. This further reduces the chances of falsely
triggering the autostart of the receiving demodulator, even when 170 Hz shift is used. Also, the
sense of the ST-6000 tones is changed with the demodulator SENSE (NORM-REV) switch, thus per-