TM 11-5805-689-14
when the ACCESS pushbutton is depressed or the
through capacitor C104 to the base of 2600 Hz tone
release timer is on, or the latch circuit is on etc. This
gate transistor Q23, and is inductively coupled to the
is accomplished by applying a logic 0 from the
four-wire send pair via send transformer T1 to the
various circuits to resistor R53. This provides base
automatic switching center. The collector of release
drive for transistor Q19 and causing it to conduct.
timer transistor Q22 is also coupled through diode
This essentially shorts out transistor Q18 Diode
CR39 to inhibit the voice circuit during the release
C R 2 8 serves two functions. First. diode - C R 3 7
sequence. I f t h e a u t o m a t i c s w i t c h i n g center
conducts when transistor Q19 conducts. to maintain
recognizes release tone and returns 570 Hz release
the 600 ohm termination on hybrid transformer T1.
acknowledge to the Converter, the action of the
Second, with diode CR37 conducting it prevents a
Converter circuitry is identical to that explained for
reversal of the polarity across capacitor C11 when:
the 2250 Hz seize tone except that when the collector
inhibit transistor Q19 conducts. The output of voice
of transistor Q12 (turn on delay transistor) switches
gate transistor Q18 is impressed across the primary
to logic 1 it is coupled through resistor R55 to the
base of transistor Q20. This essentially parallels
coming in on the two-wire port of the hybrid is in
r e s i s t o r R56 and reduces the time constant of
ductively coupled to the voice gate transistor,
capacitor C13 and resistor R56 to a nominal 1 second
which causes the timer to switch off after one second,
amplified and inductively coupled out on the four-
thus adhering to the specification of sending a
wire send pair via the secondary of the send trans-
minimum of 800 milliseconds of release tone.
former T1. The send transformer T1 is a 2:1 step
The voice gate circuit is a one stage amplifier
in on the four-wire send pair) is controlled by resistor
designed as a combination of a common base and a
R50. The diodes across the four-wire send and
grounded emitter configuration. The base circuit is
receive ports provide lightning protection and
n o t entirely AC bypassd due to the action of
clipping when the amplitude of the signals. appearing
resistor R47 which is used as a gain control. A signal
on these ports exceeds approximately 2 volts peak.
coming in on the two-wire port is coupled through
The two-wire port is terminated in a 600 ohm. resistor
capacitor C11 to the base of transistor Q18. The
when the operator is not in on the call. The four-wire
dynamic impedance of the transistor in this con-
receive and send ports are terminated by the 600
figuration, when conducting, is approximately a 600
ohm impedance presented by the automatic switch-
ohm termination across hybrid transformer T1.
ing center.
Transistor Q19 is utilized to inhibit transistor Q18
Figure 5. Converter, Telephone Signal CV-1919/G, schematic diagram