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TM 11-5820-873-34
frequency of the 2nd local oscillator and 80.75 MHz.
an internal oscillator with the VFO control on), the 1.5 to
e. VCO 1A4A5.  The voltage controlled oscillator
1.5999 MHz signal from low digit generator 1A4A2 and
the 91.25 to 121.2499 MHz signal from VCO 1A4A5,
generates the 91.25 to 121.2499 MHz, 1st local
and produces a 10.0 to 39 9 MHz signal. The 10.0 to
oscillator frequency. The variable frequency 1st local
39.9 MHz signal is coupled to VHF divider 1A4A4. The
oscillator signal controls the operating frequency of the
frequency of the 1.5 to 1.5999 MHz signal is equal to 1 5
RT-1277/URC-92. The output frequency from the VCO
MHz plus the frequency set by the selected 10 kHz, 1
is equal to the frequency set by the selected
kHz and 100 Hz FREQUENCY switches. The frequency
FREQUENCY switches plus 91.25 MHz and the
of the 91.25 to 121.2499 MHz signal from VCO 1A4A5
difference between the frequency of the 2nd local
is equal to 91.25 MHz plus the frequency set by all of
oscillator and 80.75 MHz The VCO frequency is
the selected FREQUENCY switches. The frequency of
determined by the following:
the 10.0 to 39 9 MHz signal is equal to 10.0 MHz plus
the setting of the selected 10 MHz, 1 MHz and 100 kHz
Fs - (FO + 91.25 MHz = e)
FREQUENCY switches and the difference between the
where:
frequency of the 2nd local oscillator and 80.75 MHz.
Fs = 91.25 to 121.2499 MHz signal from VCO
d. VHF Divider 1A4A4. The VHF divider generates
1A4A5
a fine steering control voltage for VCO 1A4A5.  The
Fo = Frequency set by selected FREQUENCY
inputs to the VHF divider are a 100 kHz reference signal
switches
from spectrum generator 1A4A1, a 10.0 to 39 9 MHz
e = 80.75 MHz minus the frequency of 2nd local
signal from translator 1A4A3, binary coded decimal from
oscillator
the selected 1 MHz and 100 kHz FREQUENCY switches
and binary coded decimal, representing the setting of
The VCO contains three oscillators that are
the selected 10 MHz FREQUENCY switch, from VCO
selected by the band control voltage from the selected
1A4A5.  The VHF divider compares the input signals
10 MHz FREQUENCY switch. The operating frequency
and generates a fine steering correction voltage that
of the selected oscillator is controlled by a course
represents the difference between the frequency of the
steering voltage from the selected 1 MHz FREQUENCY
91.25 to 121.2499 MHz signal from VCO 1A4A5 and the
switch and a fine steering voltage from VHF divider
frequency set by the selected FREQUENCY switches
1A4A4.
plus 91.25 MHz plus the difference between the
Figure 2-3. Synthesizer Simplified Block Diagram.
2-9

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