Hal Communications ST-6000, Инструкция по эксплуатации

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5-4
5.2.2 Antispace Circuit (Figure 5.9)
If a signal at the space frequency is held for a long period of time, the teleprinter will "run-
open", making an annoying, louder than normal noise. To prevent this problem, sections of inte-
grated circuits 2 and 3 are connected in a timer circuit that senses the length of the space signal
and places the post-autostart data signal in a mark-hold condition whenever the space exceeds
250 ms. This section of the control circuitry is always active for the post-autostart data output.
5.2.3 Pre-autostart data output (Figure 5.9)
A section of integrated circuit I2 is used to buffer and invert the output of the slicer stage and
provide a CMOS-compatible data output that is NOT controlled by either the antispace or autostart
circuits. This data-output is available on the AUXILIARY rear panel connector (J3, pin 3) for use in
those systems where the control is not desired or where user designed control circuits are to be
used.
5.2.4 Autostart Circuit (Figure 5.9)
The "plus-plus" voltage from the meter amplifier on the input circuit board is used to drive the
autostart threshold detector, integrated circuit I1. As explained previously, the "plus-plus" voltage
is proportional to the frequency match between the input tones and the discriminator filter fre-
quencies. It is only maximum and non-varying when the two tones (mark and space) match the fil-
ters. The offset bias applied to I1 is set to produce a rapid positive voltage transition at I1 output
(pin 7) whenever the "plus-plus" voltage exceeds the of f set bias voltage. In practice, this adjust-
ment should be set so that I1 does not trigger on noise pulses but does trigger whenever a valid
RTTY signal is received. This is an adjustment that the user may wish to set to his own preference.
If the threshold pot is set too close to the noise, the autostart will activate readily on noise and in-
terference; if set too high, the autostart may not trigger at all, even on good RTTY signals.
The output of I1 drives an inverting amplifier and time delay circuit that determines the auto-
start response time. The turn-on time of the autostart can be switch selected for either approxi-
mately 1.5 or 3.5 seconds (AUTOSTART, SLOW-FAST switch). The run-off time after loss of signal
is much shorter. The delayed control voltage is coupled through IC gates 13 (two sections) and 14
where it is combined with the antispace output and the standby control line to produce the post-
autostart data output. The autostart may be defeated with the front panel AUTOSTART, ON-OFF
switch.
The autostart output (as well as the standby line) also drives the motor power control circuit,
two sections of I4 plus a MPS6518 relay driver transistor. This circuit turns on the motor relay, ap-
plying power to the MOTOR receptacle when the autostart senses a valid RTTY signal. A time delay
circuit keeps the motor power on until approximately 20 seconds after the autostart senses loss-of-
signal. At this time, power to the MOTOR receptacle is turned off and remains so until another val-
id signal is sensed by the autostart or until the standby line is activated. The motor power is al-
ways on when the standby line is in standby condition (LOCAL position of the PRINT switch). The
motor circuit is NOT controlled by the antispace circuit.
5.2.5 Standby Circuit (Figure 5.9)
The third control of the post-autostart data line is the standby circuit. This can be activated by
three sources. First, the front panel PRINT (LINE - LOCAL) switch provides manual control. When
the switch is in LINE position, the post-autostart data line is controlled by the detected signal, pro-