(b) During transmission, the outgoing IF signal of 1,750 kHz from the
IF-audio module heterodynes with the synthesizer output frequency of
4,917 kHz in the balanced modulator of the RF module. The resultant
difference frequency of 3,167 kHz is the output signal of the
transmitter.
2-3.
INDIRECT-TYPE SYNTHESIZER BLOCK DIAGRAM ANALYSIS
(fig.
2-2)
To illustrate one type of frequency synthesizer of fixed-station use, we will
make a block diagram analysis of Frequency Stabilizer Kit SBM-1102. The SBM-1102
consists of two units, a frequency stabilizer (A) and an electrical and frequency
synthesizer (B). It is used as an improvement modification for Radio Receiving Set
AN/FRR-41. The AN/FRR-41 is a fixed-station dual-diversity radio receiving system,
which consists of two Radio Receivers R-390A/URR and two Single-Sideband Converters
CV-157A/URR. The SBM-1102 is used to increase the accuracy and versatility of the
receiving system.
The frequencies it provides are far more stable than the
internal frequencies generated by the receivers and converters.
Stability of
internal frequencies allows more accurate heterodyning of the intelligence signal.
The SBM-1102 allows fast, easy tuning to the received signal. It can even be used
with an unsynthesized transmitter.
If the transmitter drifts slightly from its
operating frequency the receiver can quickly be retuned to the new frequency.
a. Synthesizer Operation. Frequency Stabilizer Kit SBM-1102 does not affect the
received intelligence signals in any way.
It is connected in parallel with the
receivers and converters in the receiving system. The received signal is fed from
the antenna through the receivers and converters to the multiplex equipment. Thus,
the received signal path remains the same even with the SBM-1102 installed.
The
only difference is that now the receivers and converters are being supplied with
highly stable frequencies from the SBM-1102 and operate with extreme accuracy.
b. Relay Control Voltage. The +28 relay control voltage determines whether the
AN/FRR-41 uses its own internal frequencies for signal conversion or those provided
by the SBM-1102.
When the SBM-1102 is installed in the AN/FRR-41, the original
oscillators in the receivers and converters are not removed; they are connected
through relay circuitry to the same points they were before.
The output
frequencies of the SBM-1102 are connected to the same relay circuitry.
If the
relays are energized, they disconnect the AN/FRR-41 oscillators and connect
replacement frequencies from the SBM-1102. If the relays are deenergized, the SBM-
1102 is disconnected, and the AN/FRR-41 is connected to its own oscillators for its
mixer frequencies.
Should equipment difficulties develop in the synthesizer or
stabilizer during stabilized operation, the receiver and converters can be returned
to normal operation with negligible downtime while repairs are being made.
c. Reference Frequencies.
To generate the five frequencies required by the
AN/FRR-41 receiving system, the SBM-1102 uses a single, highly stable 1-MHz signal.
It generates the other frequencies by phase-locking other oscillators to the 1-MHz
signal.
The 1-MHz RF oscillator subassembly (A5) is located in the stabilizer
(fig. 2-2). The oscillator is called a pullable
327 L2
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