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TM 11-5820-477-30
(1) Signals present at the LINE binding posts (when the TEL-REMOTE-RADIO switch is in the REMOTE
position) are coupled through the secondary of T101 (terminals 3 and 4) to terminal of filter FL102. Filter FL102
passes only the 3,900-Hz signal and rejects all other signals. From terminal 2 of filter FL102 the 3,900-Hz signal
is applied to pins B of P102 and J104.
(2) The 3,900-Hz signal is coupled by capacitor Cl 10 to the base of 3,900-Hz amplifier Q105. Capacitor
Cl 07 couples the output of Q105 to emitter follower Q104. Resistor R111 provides a termination for filter FL102.
Resistors R108 and R110 form a voltage divider to establish the base-to-emitter forward bias for Q105. Battery
voltage is applied to the emitter of Q105 through voltage-dropping resistor R112 and emitter swamping resistor
R109. Capacitor Cl 08 bypasses resistor R112. Inductor L101 is the collector load for Q105. The 3,900-Hz
amplifier, Q105, is selectively tuned by filter FL103. Filter FL103 peaks the 3,900-Hz signal.
(3) Emitter follower Q104 is directly coupled to emitter follower Q103. The base of Q103 is biased at the
battery voltage through the low dc resistance of filter FL103. Battery voltage is applied to the emitter of Q104
through emitter swamping resistor R120. Capacitor Cl 09 integrates the output present at the emitter of Q103 and
applies this dc voltage to pin E of J104. The dc voltage present at pin E of P102 is applied through switch S102,
section A rear (contacts 6 and 8) to terminal 5 of relay K101.
(4) Battery voltage is applied to relay K101 (terminal 1) through switch S102, section B rear (contacts 12 and
10). With a 3,900-Hz signal present at the LINE binding posts, the negative-going dc output of the resonant relay
amplifier tends to cause the voltage on terminal 5 of relay K101 to approach zero. The difference in potential on
the coil of K101 causes it to energize. When K101 energizes, ground is applied throughK101 (contacts 8 and 6)
and P101 (pin C) to a circuit in the radio set, which keys the transmitter.
(5) Operating voltage for the resonant relay amplifier is applied through pins D and F of P102 and J104.
c. Attenuator. The attenuator is a pad consisting of three L sections. Resistors R114 through R119 make up
the attenuator and provide approximately 50-dB attenuation of the signal, which reduces it to the approximate
level of a microphone output.
(1) The voice and 3,900-Hz signals present at the LINE binding posts are coupled through the secondary of
T101 (terminals 3 and 4) to filter FL101 (terminal 2). Filter FL101 is a parallel-tuned filter which attenuates the
3,900-Hz signal. When relay K101 has been energized, the voice and attenuated 3,900-Hz signals at the output
of FL101 (terminal 1 ) are applied through K101 (terminals 4 and 2) to the attenuator.
(2) Output signals of the attenuator, terminal 7, are applied through switch S102, section B rear (contacts 2
and 4) to the primary (terminals 1 and 2) of transformer T102. Transformer T102 provides ground isolation
between the local control unit and the radio set. Signals induced in the secondary winding (terminals 3 and 4) of
transformer T102 are applied through filter FL104 (terminals 2 and 1) and connector P101 (pin D) to the radio set.
Filter FL104 further attenuates the 3,900-Hz signal.
d. Ringing Circuits. Magneto G101, buzzer DS101, microswitch S103, and the call lamp circuit are
functionally the same as their respective components in the remote control unit. Refer to (para. 1-13e. for
explanation of these components in the remote control unit.

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