Section II. CIRCUIT ANALYSIS

from the oscillator buffer and fss if.) is

also has an input from the 50-kc interval

compared and a control voltage is devel-

oscillator.

oped in the phase comparator. The control

g. The- 50-kc interval oscillator gen-

voltage is applied through the antihunt

erates one of three frequencies: 5.55 mc,

network to the apc modulator. If a phase

5.60 mc, or 5.65 mc. The specific fre-

quency depends on the frequency selected

lock exists, the apc voltage will assume

by the kc tuning knob (50- or 100-kc in-

the reference level to maintain the vfo on

crements) and whether the RT-505/PRC-

frequency. If a phase difference exists,

an error voltage is developed in the phase

25 is receiving or transmitting. When a

50-kc channel point (37 .45, 71.25, etc) is

comparator. This error voltage varies

selected, the 50-kc interval oscillator out-

the apc voltage applied to the apc modu-

put frequency will be 5.60 mc during recep-

lator from the reference level to correct

the operating frequency of the vfo.

tion. (During reception, relay K2 causes a

frequency shift to 5.55 me.) When a 100-kc

i. If the vfo output is too far from its

channel point (37.40, 71.20, etc) is se-

proper frequency to be corrected by the

lected, the 50-kc interval oscillator output

phase comparator output, the discrimina-

frequency will be 5.65 mc, during recep-

tor (which extends the capture range of the

tion. During transmission, relay K2 causes

fss) will develop a hunt voltage, which in-

a 50-kc shift to 5.60 mc.

creases the deviation of the apc voltage.

(1) During reception, the 50-kc inter-

Since the vfo is far from its correct fre-

val oscillator output will always be

quency, the frequency of the signal applied

5.65 mc at the 100-kc channel

to the discriminator (f above) will be con-

point; during transmission, it will

siderably removed from the proper fss if.

be 5.60 mc.

(e above). The discriminator will develop

(2) During reception, the 50-kc inter-

a large error (hunt) voltage. This hunt

val oscillator output will always

voltage which is applied through the anti-

hunt network to the apc modulator, changes

be 5.60 mc at the 50-kc channel

points; during transmission, it will

the vfo output frequency to within the pull-

be 5.55 mc.

in and hold-in capabilities of the phase

h. The output of the 50-kc interval os -

comparator. The antihunt network stops

cillator (g above) is applied as a reference

the hunting action of the vfo when the phase

signal to the phase comparator. The phase

comparator has control of the vfo fre-

of the two input signals (reference signal

quency.

Section II. CIRCUIT ANALYSIS

6. First Rf Amplifier Module A3

the power amplifier tank circuit. The out-

put of Q1 is taken from the collector

(fig. 1)

through coupling capacitor C5 and resistor

R4 to BAND switch S1. Resistor R4 sup-

First rf amplifier module A3 amplifies

presses parasitic oscillations.

the signal received from module A2 (para

20). The first rf amplifier consists of a

b. Switch S1 is positioned by the BAND

switch on the front panel. The collector

sing1e transistor amplifier, the BAND

circuit of Q1 is tuned in each of the two

switch, and tuned output circuits.

BAND positions as follows:

a. The input signal from module A2 is

(1) Low band. Transformer T2, fixed

coupled through transformer T1 and coup-

capacitor C8, trimmer capacitor

ling capacitor C 3 to the base and emitter

C7 and tuning capacitor C2C (fig.

of transistor Q1. The center-tap of the

1) make up the tuned circuit. The

secondary of T1 is returned to rf ground

position of tuning capacitor C2C is

through capacitor C2. The use of the tapped

determined by the mc and kc con-

transformer input coupling neutralizes the

trols on the front panel.

stage and isolates the rf amplifier from