Tait T800 SL2 25W, Service Manual

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M8SL2-00-002-812
Line Controlled Base without Talk Through G4.1
© Copyright Tait Electronics Limited August 2004. All rights reserved.
4 Line Controlled Base without Talk
Through
4.11 General
This installation contains a transmitter and receiver which may or may not be on the
same frequency, thus simultaneous transmission and reception is not possible. When
the transmitter is keyed, the coaxial relay is also energised. When the relay is in its rest
position, signals from the antenna are passed to the receiver and the demodulated out-
put is fed via 600
Ω
lines to the RCU.
The receiver is disabled when the transmitter is energised to prevent the receiver mute
opening from RF due to lack of isolation in the relay, direct radiation or the noise skirt of
the dual frequency link.
Since the base station may be controlled via a 2-wire line and a 4-wire to 2-wire hybrid,
there is a possibility of system oscillation if the receiver is not disabled during transmit.
This occurs when the transmit energy enters the receiver and produces an audio
response which can pass from the receive to the transmit audio part of the hybrid
(impedance imbalance, etc).
Figure 4.2 Basic Configuration
Figure 4.3 Remote Line Controlled Base Station
RF Out
Coax
Relay
DC
Key
Logic
Tx
Enable
DC Relay
Control
RF In
Tx Rx
Antenna
Rx Disable
Tx AF
RF Out
Coax
Relay
RF In
Tx Rx
Antenna
Hybrid
Rx AF
Remote
Control
Microphone
Speaker
PTT