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TM 11-5820-498-35
vided through the CX-4656/GRC (pins EC)
(1) Before the RF signals are received from
and relays K1 and K2 to the 12.5-15 volt batter
either distant radio station, the relay site re-
in receiver-transmitter No. 2.
ceiver-transmitters are in standby mode. Under
(d) With the transmitting circuits in re-
t h i s situation, the output transformers, in
ceiver-transmitter No. 2 in transmit mode by the
A25/A55 in No. 2 and T5001 in No. 3, are
operations of K1 and K2, speech signals can now
grounded through contacts of their associated
be applied from T5005 in receiver-transmitter
squelch relays. Thus, no signals can pass between
the relay site receiver-transmitters.
No. 3 through the CX-4656/GRC (pins E-C) and
the transmitting circuits in receiver-transmitter
(2) When a signal including the 150-Hz
No. 2 to the antenna for transmission to radio
squelch signal is received at receiver-transmitter
station. No.1.
No. 2, it is applied through RF-IF amplifiers and
(e) When radio station No. 4 ceases keying
the discriminator to receiver audio amplifier
its transmitter, receiver-transmitters No. 3 and 2
(3) From the discriminator, the 150-Hz
go into standby condition ((1) above).
squelch signal is applied to squelch relay control
(f) Diode CR1 in the C-E circuit of the
A24/A54. A24/A54 then provides a closed circuit
CX-4656/GRC is provided to keep the two differ-
ent battery potentials separated when the re-
to operate relay K3. When K3 operates, contacts
ceiver-transmitters No. 3 and 2 are in standby.
8-3 remove the short from output transformer in
A25/A55 ((1) above).
The diode prevents receiver-transmitter No. 2
(4) Simultaneously, ground on the output
from going into transmit mode by the operation
transformer in A25/A55 is provided through
of K1 and K2. Under this condition, the circuit
function switch S1 and applied through diode
performs as follows:
CR2 in the CX-4656/GRC and through receiver-
transmitter No. 3 relays K405 and K401 to the
If the CX-4656/GRC cable connects to the
25-volt battery. Thus, contacts 4-7 of K1 provide
receiver-transmitters shown in figure 4-8
operating power continuity to receiver-transmit-
diode CR2 in the C-E circuit would perform
ter No. 3 transmitting circuits by the operation of
the operations described for CR1 below.
relays K405 and K401.
(5) With the transmitting circuits in re-
1. When receiver-transmitter No. 2 is
ceiver-transmitter No. 3 in transmit mode, speech
connected to another RT-505/PRC-25 or
signals can now be applied from receiver-trans-
RT-841/PRC-77, a squelch signal received by No.
2  A25/A55
mitter No.
3 provides a simple ground to the battery in No. 2
C X - 4 6 9 6 / G R C to receiver-transmitter No. 3
which causes relays K1 and K2 to operate for
transmit circuits, and to the antenna for trans-
transmission (fig. 4-3 and para 2-7 b(4)).
mission to radio station No. 4.
(6) When radio station No. 1 ceases keying
2. However, when an RT246(*)/VRC
its transmitter, receiver-transmitters No. 2 and 3
or RT-524(*)/VRC is used as receiver-transmit-
go into standby condition ((1) above).
ter No. 3, there are two different battery poten-
(7) When radio station No. 4 keys its trans-
tials, 12.15 volts in No. 2 and 25 volts in No. 3.
mitter and transmits its signals, the operation of
If there were no diode CR1 in the CX-4656/GRC
the circuits in receiver-transmitters No. 3 and 2
when the receiver-transmitters are in standby,
are accomplished as follows:
the two batteries would be connected in series (B,
(a) When a signal including a squelch
fig. 4-8). When two such opposing potentials
signal (150-Hz or noise) is received at receiver-
meet, a voltage difference (between 10 and 12.5
transmitter No. 2, it is applied through the re-
volts) would be sufficient to operate K1 and K2
ceive circuit.
into transmit mode in receiver-transmitter No. 2.
(b) In the receive circuit, the squelch sig-
nal is applied to squelch control A5200, causing
3. The diode in CX-4656/GRC preven
squelch relay K5002 to operate. When K5002 oper-
this extra voltage from operating K1 and K2. The
ates, a ground is provided through contacts 2-5
remaining voltage is blocked because the poten-
of K505, CR303 (in RT246(*)/VRC), or CR351
tial (which takes on the polarities of the 25-volt
(in RT-524(*)/VRC), and the CALL lamp to the
battery) would apply a negative potential to the
25-volt battery.
anode of the diode. Thus, no current can flow
(c) At the same time, the ground is pro-
operate K1 and K2 in receiver-transmitter No. 2.

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