The rf amplifier and driver stages

TM 11-5820-509-35

rejection and reduce adjacent-channel interference by

c. The rf amplifier and driver stages, as shown in

improving the input selectivity during receiver operation.

figure 7-12, are conventional vacuum-tube amplifiers

Receiver overloading is minimized by the use of

with bandswitching plate tank circuits. In the transmit

automatic gain control techniques. The agc bias applied

mode, the rf signal from amplifier Ql5 is applied to the

to the control grid circuits of rf amplifiers V1 and V2 is

grid circuit of first rf amplifier V1, routed to second rf

obtained from circuits in audio frequency amplifier AI

amplifier V2, and further amplified by driver V3 before

(pare 2-9d).

being applied to the grid circuit of the power amplifier

d. The hf oscillator signal is generated by transistor

stage. The rf amplifier/driver bandswitching circuits are

Q20 using the shunt- and series-tuned circuits

coarse-tuned by adjustment of the whole megahertz

associated with bandswitches S6 and S10. Oscillator

frequency control knob on the front panel of the RT-671

Q20 is a common-base Colpitts configuration that

/PRC-47. As this selection is made, a switch position is

employee voltage-controlled capacitors in a shunt

selected that connects an appropriate tuned circuit

network across the frequency-determining tank circuit to

component to each stage. The bands of frequencies

provide automatic error-correction of the transmitter-

that are selected at each switch position is shown in the

receiver operating frequency by compensating voltages

following table

developed in the discriminator circuits of oscillator

control A7. Coarse frequency control of the hf oscillator

Bandswitch

KILOCYCLES indicator

(vfo) is provided by ganging the hf oscillator

position

reading (MHz.)

bandswitches with the whole megahertz frequency

control shaft that adjusts the rf amplifier and driver

2.000 to 2.999

circuits.

Fine frequency control is provided by

3.000 to 3.999

application of error-correcting voltages to the error volts

4.000 to 4.999

A and/or error volts B inputs that control varicaps CR9

5.000 to 5.999

and CR10. A small time lag exists between the

6.000 to 6.999

application of the error voltage by the discriminator

7.000 to 7.999

circuits of oscillator control A7 and the change in hf

8.000 to 8.999

oscillator frequency. This is largely due to the slow

9.000 to 9.999

response of the varicap capacitance. As a result, some

10.000 to 10.999

over-correction can occur and some hunting exists

11.000 to 11.999

during the frequency control mode. The 2.5- to 12.499-

hf oscillator signal is amplified and buffered by Q21

Fine tuning by adjustment of the 100- and 10-kHz

before application to follower Q2 and the isolation

frequency control knobs on the front panel of the

amplifier circuits. Capacitor C344 and slug rack L145

receiver-transmitter varies the inductance of series coils

permit the initial hf oscillator frequency settings to be

L1 through L5 and L145 to obtain proper tracking.

made prior to tracking adjustments. Potentiometer

When the receive mode is selected, the additional tuned

R162 in the base of buffer amplifier Q21 permits the hf

circuits associated with bandswitches S1, S2, and S3

oscillator output level to be con troled over narrow

are inserted in the grid circuit of the first rf amplifier

limits.

(V1). These grid circuit components are ganged with

the whole megahertz, 100-kHz, and 10-kHz frequency

control knobs and are adjusted with the plate circuit

components. These additional tuned circuits in the grid

of V1 provide greater image

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