Tone Generator (Q204 and Q205)

TM 11-5820-477-30

(2) Audio amplifier Q202. The input audio signals to Q202 are amplified by approximately 33 dB.

Capacitors C204, C205, and C206 and resistors R203, R204, and R207 are functionally the same as their

respective components in the Q201 circuit (para 1-13a.(1)). Resistor R227 acts as part of the emitter resistance

and also provides degenerative feedback. The preamplifier output is connected through pin H on J204 and P201

to the primary (terminals 1 and 2) of audio line transformer T201. Terminal 2 of T201 is grounded through CR201

and the push-to-talk switch of the handset. The induced voltage into the secondary of T201 (terminals 5 and 6) is

applied to LINE binding posts J202 and J203. Battery voltage is applied to the preamplifier through pin J of J204.

b. Tone Generator (Q204 and Q205). The tone generator consists of oscillator Q204 and audio amplifier

Q205.

Oscillator Q204, a modified shunt-fed Hartley oscillator, produces the 3,900-Hz signal tone which activates circuits

in the local control unit to key the transmitter portion of the radio set. Audio amplifier Q205 amplifies the 3,900-Hz

output oscillator of Q204.

(1) Oscillator Q204. Oscillator circuit Q204 begins generating noise when battery voltage is applied. Tuned

tank circuit filter FL202 allows only the frequency to which it is tuned (3,900-Hz) to pass to the transistor base.

Capacitor C212 couples the 3,900-Hz output to the base of audio amplifier Q205.

(a) Capacitor C211 is the coupling capacitor for the feedback loop. Resistor R219 reduces the

amplitude of the feedback signal. Resistors R217 and R218 form a voltage divider t hat establishes the forward

and reverse bias levels. Capacitor C210 bypasses resistor R218. Resistor R220 is the emitter swamping resistor.

(b) When the handset push-to-talk switch is pressed, battery voltage is applied through terminal 4 of

component board A201. The TEL-RAD-RAD/SPKR switch must be in RAD or RAD/SPKR position.

Audio amplifier Q205. Audio amplifier Q205 provides the output of the oscillator with a gain of

(2)

approximately 35 dB. All parts of audio amplifier Q205, except R226, are functionally the same as their respective

parts in audio amplifier Q202 (para. 1-13a.(2)). Resistors R226 and R221 forma signal voltage divider to reduce

signal amplitude at the base of Q205. The 3,900-Hz output signal is connected to the primary (terminals 1 and 2)

of T201 through terminal 1 of component board A201. The 3,900-Hz tone and audio signals are coupled to the

secondary of T201 (terminals 5 and 6) to the LINE binding posts. Battery voltage is applied through terminal 3 of

component board A201.

c. Audio Driver Q203. Audio driver Q203 amplifies the signals from the receiver section of the associated

radio set by approximately 25 dB.

(1) Signals present at pin B of J204 are coupled by capacitor C208 to the base of audio driver Q203.

Resistors R209, R210, and R213 establish the bias voltage for Q203. Capacitor C207 and resistor R209 provide

alternating current (ac) decoupling for the battery voltage. Resistor R211 is the emitter swapping resistor

bypassed by capacitor C209. Resistor R212 provides degenerative feedback.

(2) Output signals of audio driver Q203 are applied through pin E of J204 and P201 to terminals 1 and 2 of

transformer T202. Battery voltage is applied to Q203 through pins F and D of P201 which mate with pins F and D

of J204.

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