Hal Communications ST-6000, Instruction Manual

Page: 43 / 70

5-5
viding the autostart has activated. When in LOCAL position, the post-autostart data line is locked in
mark condition and the motor is held on for "local loop" types of operation. This same control line
can be controlled externally through the Remote Standby connection on the AUXILIARY connector
(J3, pin 2). When this line is at +12 Volts, the post-autostart data line can be driven by the detect-
ed signal. When the line is grounded, the post-autostart data output is held in mark-hold. The third
control of the standby circuit is by the KOS circuit. Whenever the KOS circuit is in transmit mode,
the post-autostart output is locked in mark condition to provide local loop operation (in half- du-
plex operation) and to prevent re-triggering of the loop that might be caused by reception and de-
tection of the transmitted signal.
5.2.6 Post-autostart Data Output (Figure 5.9)
The outputs of the antispace circuit, the autostart circuit, and the standby control line are com-
bined in gate I4 and buffered in I2 to give a post-autostart data output of the ST-6000. This data
signal is connected to pin 10 of the AUXILIARY rear panel connector (J3). Either this signal or the
pre-autostart data signal can be used to drive the loop stages. the RS-232-/MIL-188 interfaces, or
external equipment, as selected by jumpers on the AUXILIARY connector. The standard jumper
plug furnished with the ST-6000 connects the post-autostart data signal to drive the loop keyer
stages. Both the pre- and post-autostart data signals are CMOS logic signals with mark = 0 Volts
and space = +12 Volts. Part of the versatility of the ST-6000 lies in the fact that these signals are
available for external connection and can be jumpered to suit individual requirements.
5.2.7 Loop Keyer Stages (Figure 5.10)
The ST-6000 has two high-voltage loop keyer stages that can be connected to drive up to two
different loop circuits. Both keyer stages are driven by the output of gate I10. Two inputs to this
gate are provided on the AUXILIARY connector; Transmit Loop Drive (pin 13) and Receive Loop
Drive (pin 6). Either input can be used to drive the keyer stages with the reservation that the Re-
ceive Loop Drive input is also used to drive a circuit to differentiate between keyboard interrup-
tions of the loop and loop keying due to received data. Both inputs require CMOS-compatible levels
(mark = 0, space = +12 V.). The standard jumper plug for the AUXILIARY connector connects the
post-autostart data output (pin 10) to the Receive Loop Drive input (pin 5).
Both keyer stages use a type 2N5655 keying transistor, rated at 100 mA (mark) or +200 volts
(space) maximum. Both have series RC transient protection across the collector circuits. One of
these stages is called the "Main Keyer" stage and has its collector connected to pin 4 of the Loop 1
& 2 connector (J8), where it is called "Loop 1". The emitter of this "Main Keyer" stage has a series
resistor to ground to sense the loop current through the transistor. This signal is amplified by a
MPS3394 to produce a CMOS-compatible output signal that has the same data as Loop 1, whether
it originates from a received signal or from external devices in the loop (such as from a keyboard,
tape transmitter, or other device). This output signal is called "Loop Sense" and is connected to
pin 11 of the AUXILIARY connector (J3). The standard jumper plug for the AUXILlARY connector
uses this signal to drive the tone keyer input (pin 15) and the RS-232/MIL-188 data output interfa-
ces. This Loop Sense signal is also combined with the Receive Loop Drive signal in gate 1 to pro-
duce the Loop Keyboard output signal (pin 1, J3). The Loop Keyboard output signal is again
CMOS-compatible and represents ONLY the data generated in the loop EXTERNAL to the ST-6000.
This signal is normally jumpered in the standard AUXILIARY jumper plug to drive the KOS circuit
(jumper from pin 1 to pin 5 of J3).
The other keyer, called the "Auxiliary Keyer" stage, simply switches to ground on mark and does
not have a current sensing circuit. The collector of this keyer transistor is connected to pin 2 of the
Loop 1 & 2 connector (J8), where it is referred to as "Loop 2". This second loop keyer can be used