f. Frequency Stability.
In this synthesizer, four crystals are always used to
obtain one output frequency.
Instability in any one or more of these crystals
causes a comparable variation in output frequency.
To compensate for this
variation, capacitor C601 is placed in series with the selected crystal in assembly
Al during receiving.
The receiving operator varies the C601 to obtain the best
quality signal; therefore the label CLARIFY.
Capacitor C601 is automatically
removed from the circuit during transmission by the action of relay K1.
g. Calibration. An adjustable capacitor is wired in parallel with each crystal
in assembly Al for minor frequency adjustment.
To make this adjustment, a
frequency standard is required.
Crystal Y41 (6,525 kHz) establishes a reference
frequency for this purpose. The crystal is applied to oscillator Q1 by relay K2.
To select the output frequency of the radio set, the operator
merely selects the desired frequency by means of the four step frequency selector
controls in the frequency synthesizer.
For example, assume the radio output
frequency to be 3,167 kHz, of 3.167 MHz. The operator will set his step frequency
selector controls as follows:
(1) Table I shows that the frequency for switch position 7 in the 1 kHz column
is 6,532 kHz.
(2) Frequency for switch position 6 in the 10 kHz column is 9,085 kHz.
(3) Frequency for switch position 1 in the 100 kHz column is 26,830 kHz.
(4) The sum of these frequencies is 42,447 kHz.
(5) The difference between 42,447 and 37,530 is 4,917 kHz.
This is the output
frequency of the synthesizer.
(a) During reception, the incoming frequency of 3,167
kHz heterodynes with
the synthesizer output frequency of 4,917 kHz in
a balanced modulator
in the RF module (not shown in figure 2-1). The
of 1,750 kHz is the intermediate frequency (IF)
required by the IF-
audio module in the radio set.