Operator`s manual

also has an input from the 50-kc interval
oscillator.
g. The- 50-kc interval oscillator gen-
erates one of three frequencies: 5.55 mc,
5.60 mc, or 5.65 mc. The specific fre-
g
quency depends on the frequency selected
by the kc tunin knob (50- or 100-kc in-
crements) and whether the RT-505/PRC-
25 is receiving or transmitting. When a
50-kc channel point (37 .45, 71.25, etc) is
selected, the 50-kc interval oscillator out-
put frequency will be 5.60 mc during recep-
tion. (During reception, relay K2 causes a
frequency shift to 5.55 me.) When a 100-kc
channel point (37.40, 71.20, etc) is se-
lected, the 50-kc interval oscillator output
frequency will be 5.65 mc, during recep-
tion. During transmission, relay K2 causes
a 50-kc shift to 5.60 mc.
(1)
(2)
During reception, the 50-kc inter-
val oscillator output will always be
5.65 mc at the 100-kc channel
point; during transmission, it will
be 5.60 mc.
During reception, the 50-kc inter-
val oscillator output will always
be 5.60 mc at the 50-kc channel
points; during transmission, it will
be 5.55 mc.
h. The output of the 50-kc interval os -
cillator (g above) is applied as a reference
signal to the phase comparator. The phase
of the two input signals (reference signal
from the oscillator buffer and fss if.) is
compared and a control voltage is devel-
oped in the phase comparator. The control
voltage is applied through the antihunt
network to the apc modulator. If a phase
lock exists, the apc voltage will assume
the reference level to maintain the vfo on
frequency. If a phase difference exists,
an error voltage is developed in the phase
comparator. This error voltage varies
the apc voltage applied to the apc modu-
lator from the reference level to correct
the operating frequency of the vfo.
i. If the vfo output is too far from its
proper frequency to be corrected by the
phase comparator output, the discrimina-
tor (which extends the capture range of the
fss) will develop a hunt voltage, which in-
creases the deviation of the apc voltage.
Since the vfo is far from its correct fre-
quency, the frequency of the signal applied
to the discriminator (f above) will be con-
siderably removed from the proper fss if.
(e above). The discriminator will develop
a large error (hunt) voltage. This hunt
voltage which is applied through the anti-
hunt network to the apc modulator, changes
the vfo output frequency to within the pull-
in and hold-in capabilities of the phase
comparator. The antihunt network stops
the hunting action of the vfo when the phase
comparator has control of the vfo fre-
quency.
Section II. CIRCUIT ANALYSIS
6. First Rf Amplifier Module A3
(fig. 1)
First rf amplifier module A3 amplifies
the signal received from module A2 (para
20). The first rf amplifier consists of a
sing1e transistor amplifier, the BAND
switch, and tuned output circuits.
a. The input signal from module A2 is
coupled through transformer T1 and coup-
ling capacitor C 3 to the base and emitter
of transistor Q1. The center-tap of the
secondary of T1 is returned to rf ground
through capacitor C2. The use of the tapped
transformer input coupling neutralizes the
stage and isolates the rf amplifier from
the power amplifier tank circuit. The out-
put of Q1 is taken from the collector
through coupling capacitor C5 and resistor
R4 to BAND switch S1. Resistor R4 sup-
presses parasitic oscillations.
b. Switch S1 is positioned by the BAND
switch on the front panel. The collector
circuit of Q1 is tuned in each of the two
BAND positions as follows:
(1) Low band. Transformer T2, fixed
capacitor C8, trimmer capacitor
C7 and tuning capacitor C2C (fig.
1) make up the tuned circuit. The
position of tuning capacitor C2C is
determined by the mc and kc con-
trols on the front panel.
7