Synthesizer 1A4 Detailed Functional Operation

TM 11-5820-873-34

(5) 17 MHz Reference Generator. The third

2-9.

Synthesizer

1A4

Detailed

Functional

harmonic of the 1 MHz pulse from 1A4A1U4 ((2) above)

Operation (Fig. FO-3, and FO-18 thru FO-23)

is amplified by 3 MHz amplifier 1A4A1Q5. The 3 MHz

The synthesizer generates the three local oscillator

output from 1A4A1Q5 is applied to 17 MHz mixer

injection frequencies used in the IF circuits of the radio.

1A4A1Q6. The other input to 1A4A1Q6 is the 20 MHz

The 3rd local oscillator frequency is fixed at 10.5 MHz

signal from 1A4A1U3 ((1) above). The two inputs are

and is generated by spectrum generator 1A4A1 (a

mixed in 1A4A1Q6 and the 17 MHz difference

below). The 2nd local oscillator frequency is fixed at

frequency is filtered by the bandpass filter. The 17 MHz

80.75 MHz and is generated by translator 1A4A3 (c

output of the bandpass filter is coupled through amplifier

below). The 1st local oscillator frequency is variable

(complementary emitter follower) 1A4A1Q7, 1A4A1Q8

and controls the operating frequency of the radio. The

to low digit generator 1A4A2 (b below).

1st local oscillator frequency is generated by VCO

(6) 21 MHz Reference Generator. The 1 MHz

1A4A5 (e below). The signals used to control the 1st

pulse from 1A4A1U4 ((2) above) is filtered by the 1 MHz

local oscillator frequency are generated in other areas of

bandpass filter. The 1 MHz sinewave from the 1 MHz

the synthesizer. The frequency of some of these signals

bandpass filter is amplified by complementary emitter

is controlled by the setting of the selected FREQUENCY

follower 1A4A1Q1, 1A4A1Q2. The 1 MHz sinewave

control switches. Table 2-1 lists the points where

from the complementary emitter follower is applied to

programmed frequencies and division ratios can be

balanced mixer 1A4A1CR4 thru 1A4AiCR7. The other

found in the synthesizer. The table also shows the

input to be balanced mixer is the 20 MHz signal from

frequency or division ratio at these points for various

1A4A1U3 ((1) above).

The 20 MHz signal from

settings of the selected FREQUENCY control switches.

1A4A1U3 is amplified by 1A4A1U8 and applied to the

a. Spectrum Generator 1A4A1 (Fig. FO-3 and Fig.

balanced mixer. The 21 MHz sum frequency is filtered

FO-18).

by the 21 MHz bandpass filter and amplified by

(1) 20 MHz Reference Generator. The 5 MHz

1A4A1U9.

The 21 MHz signal from 1A4A1U9 is

reference signal from TCXO 1A8U1 is amplified by

coupled through emitter follower 1A4A1Q9 to translator

1A4A1U1 and clipped by the diode clipper. The positive

1A4A3 (c below).

going half waves from the diode clipper are inverted by

(7) 10.5 MHz 3rd Local Oscillator Signal. The 21

1A4A1U2A. The output of 1A4A1U2A is applied to

MHz signal from 1A4A1U9 ((6) above) is coupled to

divide-by-5 counter 1A4A1U4 ((2) below) and one shot

divide-by-2 counter 1A4A1U10.

When the RT-

1A4A1U2B, 1A4A1U2C. The 5 MHz pulse from the one

1277/URC-92 is operating in the AM receive mode, or if

shot is inverted by 1A4A1U2D. The fourth harmonic of

the setting of the selected 1 MHz FREQUENCY switch

this 5 MHz pulse (20 MHz) is filtered by the 20 MHz

is changed while transmitting switch 1A4A1Q3 is turned

bandpass filter and amplified by 1A4A1U33. The 20

on disabling 1A4A1U10. At all other times 1A4A1Q3 is

MHz pulse output from 1A4A1U3 is applied to low digit

off and 1A4A1U10 divides the 21 MHz input by 2. The

generator 1A4A2 (b below), 17 MHz mixer 1A4A1Q6

10.5 MHz output from 1A4A1U10 is coupled through

((5) below) and 20 MHz amplifier 1A4A1U8 ((6) below).

emitter follower 1A4A1Q4 to receiver/exciter 1A3.(para

(2) 1 MHz Reference Generator. The 5 MHz

2-4).

signal from inverter 1A4A1U2A ((1) above) is applied to

b. Low Digit Generator 1A4A2 (Fig. FO-3 and Fig.

divide-by-5 counter 1A4A1U4. The 1 MHz output from

FO-21)

1A4A1U4 is applied to divided-by-10 counter 1A4A1U5

(1) Voltage Controlled Oscillator 1A4A2. VCO

((3 below), through the 1 MHz bandpass filter to

1A4A2Q1, 1A4A2Q2 is a Colpitts oscillator with a

amplifier 1A4A1Q1, 1A4A1Q2 ((6) below) and to 3 MHz

frequency range of 15 0 to 15 999 MHz. The oscillating

amplifier 1A4A1Q5 ((5) below).

frequency of the VCO is equal to the setting of the

(3) 100 kHz Reference Generator. The 1 MHz

selected 10 kHz, 1 kHz and 100 Hz FREQUENCY

pulse from 1A4A1U4 ((2) above) is applied to divideby-

switches times 10, plus 15 MHz. Coarse frequency

10 counter 1A4A1U5 The 100 kHz output from

tuning is provided by the action of the coarse frequency

1A4A1U5 is applied to VHF divider 1A4A4 (d below) and

voltage (from the selected 10 kHz FREQUENCY switch)

to divide-by-10 counter 1A4A1U6 ((4) below)

on varactor diodes 1A4A2CR1, 1A4A2CR2.

Fine

(4) 1 kHz Reference Generator. The 100 kHz

frequency control is provided by comparing the output of

pulse from 1A4A1U5 ((3) above) is applied to divideby-

the VCO with the 17 MHz and 1 kHz signals from

10 counter 1A4A1U6 The 10 kHz pulse from 1A4A1U6

spectrum generator 1A4A1 (a above). Phase detector

is applied to divlde-by-10 counter 1A4A1U7 The 1 kHz

1A4A2U2 ((4) below) develops an output voltage that is

pulse from 1A4A1U7 is applied to low digit generator 1

proportional to the difference between the frequency of

A4A2 (b below).

the VCO and the desired frequency of the VCO This

voltage is applied to varactor

2-10