Figure 2-3. Synthesizer Simplified Block Diagram.

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