Hal Communications ST-6000, Инструкция по эксплуатации

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4-7
In this case, the user will have to make his own, separate provisions for control of the received da-
ta during transmit.
4.9 The KOS Circuitry
The ST-6000 includes an automatic transmit-receive circuit that functions in a manner very simi-
lar to that of a VOX circuit in a SSB transmitter. This is the KOS (Keyboard Operated Switch) circuit.
The KOS circuit senses and differentiates between received data (from the demodulator section)
and data to be transmitted (from the keyboard, tape distributor, etc.). Whenever transmit data is
sensed , the KOS output keying transistor is turned "on" (low impedance to ground). If the PTT
(Push-To-Talk) line of the transmitter is connected to the KOS line of the ST-6000, the transmitter
will automatically go on whenever transmit data is sensed. Also, the KOS circuit senses the status
of the CW-ID input to the tone keyer and stays in transmit mode as long as the CW-ID key is ac-
tive. The operation of the KOS circuit is as follows:
1. The KOS is turned "on" (transmit condition) when:
a. The keyboard circuit goes to space condition (open circuit) for more than approximately
5 ms.
b. The CW-ID key is closed.
2. The KOS is turned "off" (receive condition) when:
a. The keyboard circuit remains in space condition for more than 0.5 second.
b. The keyboard circuit remains in mark condition for an adjustable time period between 1
and 10 seconds.
c. One second after the last CW-ID key closure.
The connections on the standard AUXILIARY jumper plug supplied with the demodulator allow
the keyboard and printer to be series-connected in the same loop. In this case, the logic of the
KOS circuit senses whether the loop has been interrupted by a received signal or by the keyboard
(or other, external device in the loop). The KOS is only allowed to turn-on (transmit mode) when
the loop interruptions are NOT caused by receive signals. Thus, the ST-6000 KOS circuit does not
necessarily require separate keyboard and printer connections as have previous similar circuits. If
the AUXILIARY jumpers are changed, a separate keyboard circuit can be used to trigger the KOS
or the presence of either RS-232 or MIL-188 input data can also be used trigger the KOS circuit.
When the KOS is used, typing on the keyboard will turn the transmitter on and inhibit the data
drive to the loop keyer stage. Use of the CW-ID key will also turn the transmitter on or keep it on,
as the case may be. The transmitter can be turned off rapidly by simply holding down the break
key for more than 0.5 sec. or by pausing for more than the preset time (1 to 10 sec.). The KOS
mark-hold time is adjusted with a potentiometer mounted on the control board directly behind the
midpoint between the AUTOSTART ON-OFF switch and the KOS switch. The potentiometer is in
the second line of ICs back from the front panel.
In order to avoid distortion of the first character typed, it is recommended that the transmission
be started with some non-essential character, such as a blank or space. If it is not desired to use
the KOS circuit, turn it off with the front panel switch provided. When connecting the KOS transis-
tor to the PTT line, be sure to observe the voltage and current limitations given in section 3.2.5.
4.10 Use of the Autostart Circuitry
The ST-6000 autostart circuit operates in a manner very similar to that of the ST-5 and earlier
TT/L and TT/L-II demodulators. The autostart provides a two-step control of the printer mark-hold
and control of the AC power to the printer motor. The autostart circuit senses the voltage on the
"plus-plus" line, which is, as described previously, proportional to the frequency match between