Phase Detector and Loop Filter.

TM 11-5820-873-34

has not gone low. With the exception of the input that is

1A4A2U7, divide-by-10 counter 1A4A2U8 will assume a

connected to pulse generator 1A4A2U7, all of the inputs

count of one instead of the preset count, since a data

to count filled detector 1A4A2U3 are high. On the next

strobe pulse was not received from preset generator

output pulse from pulse generator 1A4A2U7, the count

1A4A2U4. Divide-by-10 counter 1A4A2U8 will have an

will be 1877 (the preset count) When the output from

output at pin 12 after every 10 input pulses until preset

1A4A2U7 goes high, it will put a high on the only input to

by the next data strobe pulse ((c) below).

1A4A2U3 that is low and 1A4A2U3 will output a 50

nanosecond pulse. On the trailing edge of the pulse

preset to a count of two ((a) above). The outputs at pins

from 1A4A2U3 preset generator 1A4A2U4 will output a

5 and 12 are low. As described in ((b) above), 1A4A2U8

75 nanosecond pulse. The output from 1A4A2U4 is

will have 7 outputs after 67 inputs from 1A4A2U7. After

coupled to phase detector 1A4A2U2 ((4) below) and to

seven outputs from 1A4A2U8, the count in 1A4A2U9 will

the data strobe inputs of the preset counter

be nine (preset of two, plus seven counts). At the count

(4) Phase Detector and Loop Filter.

Phase

of nine, the output at pin 12 will be high because of the

detector 1A4A2U2 compares the output frequency of the

nine count and the output at pin 5 will be high because

preset counter ((3) above) with the 1 kHz reference

the count is an odd number. On the trailing edge of the

signal from spectrum generator 1A4A1 (a above) and

next input pulse to 1A4A2U9 (77 inputs to 1A4A2U8),

develops a DC output voltage that is proportional to the

the outputs at pins 5 and 12 will both go low. When pin

two signals. The output of the preset counter will be 1

12 goes low, 1A4A2U10 will advance one count. On the

kHz when the VCO is operating at the desired frequency

trailing edge of the next input pulse (87 inputs to

If the output of the VCO is high, the output frequency of

1A4A2U8), 1A4A2U9 will assume a count of one instead

the preset counter will be less than 1 kHz. The output

of the preset count, since a data strobe pulse was not

voltage from the phase detector will decrease, causing

received from preset generator 1A4A2U4. Divide-by-10

the operating frequency of the VCO to decrease. If the

counter 1A4A2U9 will have an output at pin 12 after

output of the VCO is low, the output frequency of the

every 10 input pulses (100 inputs to 1A4A2U8) until

preset counter will be more than 1 kHz. The output

preset by the next data strobe pulse ((e) below).

voltage from the phase detector will increase, causing

(d) Divide-by-10 counter 1A4A2U10 has been

the operating frequency of the VCO to increase. The

preset to a count of one ((a) above). The output at pin 5

loop filter removes any 1 kHz components in the phase

is high and the output at pin 12 is low. As described m

detector output and also determines the transient

((b) and (c) above), 1A4A2U9 will have 8 outputs after

response of the loop.

777 inputs to 1A4A2U8. After eight outputs from

(5) Output Divider.

The output from buffer

1A4A2U9, the count in 1A4A2U10 will be nine (preset at

1A4A2U1 ((1) above) is amplified by driver 1A4A2Q5.

one, plus eight counts). At the count of nine, the output

Divide-by-10 counter 1A4A2U5 divides the signal from

at pin 12 will be high because of the nine count and the

1A4A2Q5 and the 1.50 to 1.5999 MHz output signal is

output at pin 5 will be high because the count is an odd

fed through the 1 55 MHz bandpass filter and emitter

number. On the trailing edge of the next input pulse to

follower 1A4A2Q6 to translator 1A4A3 ((c) below).

1A4A2U10 (877 inputs to 1A4A2U8), the outputs at pins

c. Translator 1A4A3 (Fig. FO-3 and FO-20)

5 and 12 will both go low. When pin 12 goes low,

(1) Voltage Controlled Crystal Oscillator. With

1A4A2Ull will advance one count. On the trailing edge

the VFO control pulled out (on), + 12 volts is applied to

of the next input pulse (977 inputs to 1A4A2U8),

21 MHz reference amplifier 1A4A3U1 disabling the

1A4A2U10 will assume a count of one instead of the

amplifier. The same + 12 volts turns voltage controlled

preset count, since a data strobe pulse was not received

crystal oscillator 1A4A3Q1 and switch 1A4A3Q3.

from preset generator 1A4A2U4. Divide-by-10 counter

Turning on 1A4A3Q3 enables amplifier 1A4A3U2.

1A4A2U10 will go high at pin 12 after the next nine input

1A4A3Q1 is a crystal controlled Colpitts oscillator

pulses (900 inputs to 1A4A2U8).

operating In the frequency range of 20.995 to 21 005

(e) The output from divide-by-two counter

MHz. The control voltage from the VFO control is

1A4A2Ull is high because the output from 1A4A2U10

applied through control amplifier 1A4A3Q3 to the

went low after 877 inputs to 1A4A2U8 ((d) above). After

varactor diodes in the circuit to control the operating

999 more inputs to 1A4A2U8 the count will be 1876. All

frequency of 1A4A3Q1. The output from 1A4A3Q1 is

of the divide-by-10 counters will have a count of 9. The

amplified by 1A4A3U2 and applied to the 19 MHz

outputs at pin 5 will be high because the count is an odd

balanced mixer ((3) below).

number and the outputs at pin 12 will be high because of

(2) 21 MHz Reference Amplifier. With the VFO

the nine count. The output from divide-by-two counter

control pushed in (off), 1A4A3Q1 and 1A4A3U2 are

1A4A2U11 is still high because the output of 1A4A2U10

2-12