19 MHz Balanced Mixer.

TM 11-5820-873-34

d. VHF Divider 1A4A4 (Fig. FO-3 and Fig. FO-21).

disabled and 21 MHz reference amplifier 1A4A3U1 is

enabled. The 21 MHz reference signal from spectrum

(1) Broadband Amplifier, Divide-by-Four Counter,

generator 1A4A1 (a above) is amplified by 1A4A3U1

and Driver. The 10.0 to 39.9 MHz signal from translator

and applied to the 19 MHz balanced mixer ((3) below).

1A4A3 (c above) is amplified and applied to divide-by-

(3) 19 MHz Balanced Mixer. The 21 MHz signal

four counter 1A4A4U2. The 2.5 to 9.975 MHz signal

from the 21 MHz reference amplifier ((2) above) or the

from 1A4U2 is inverted by driver 1A4A1U1 and applied

voltage controlled crystal oscillator ((1) above) is mixed

to the inputs of the preset counter and the preset

with the 1.50 to 1.5999 MHz signal from low digit

generator ((2) below).

generator 1A4A2 (b above) in the 19 MHz balanced

(2) Preset Counter, Carry Detector and Preset

mixer. The difference frequency output is filtered by the

Generator. The preset counter and preset generator are

19.45 MHz bandpass filter and amplified by 1A4A3U3.

similar to the preset counter and preset generator in the

Diodes 1A4A3CR5 and 1A4A3CR12 provide AGC to

low digit generator (b(3) above). The major differences

amplifier 1A4A3U3 to ensure a constant level 19.4001

are a carry detector is used when the selected 100 kHz

to 19.50 MHz signal out. The 19.4001 to 19.50 MHz

FREQUENCY switch is set to 0 and divide-by-four

signal from 1A4A3U3 is applied to 81.25 MHz mixer

counter 1A4A4U7 is preset by the 10 MHz preset gate

1A4A3Q11 (6) below.

instead of directly from the selected 10 MHz

(4) 2nd Local Oscillator. The 2nd local oscillator

FREQUENCY switch.

is a crystal controlled Colpitts oscillator operating at

(a) Preset Counter.

The preset counter

80.75 MHz.

The output from 2nd local oscillator

consists of two divide-by-10 counters (1A4A4U3 and

1A4A3Q7 is applied to 100 MHz mixer 1A4A3Q8 ((5)

1A4A4U6) and one divide-by-four counter (1A4A4U7).

below) and through buffer amplifier 1A4A3Q9 to

The counter will divide by the number the selected 10

receiver/exciter 1A3 (para 2-4).

MHz, 1 MHz and 100 kHz FREQUENCY switches are

(5) 100 MHz Mixer. The 80.75 MHz signal from

set at plus 100 (table 2-1).

the 2nd local oscillator ((4) above) is mixed with the 20

(b) Carry Detector. When all four 100 kHz

MHz reference signal from spectrum generator 1A4A1

preset lines are programmed to a 0 state by the front

(a above) in 100 MHz mixer 1A4A3Q8. The sum

panel switches (corresponding to a dial setting of 0 on

frequency output is filtered by the 100.75 MHz bandpass

the selected 100 kHz FREQUENCY switch), a special

filter and applied to 81.25 MHz mixer 1A4A3Q11 ((6)

carry signal must be generated to program the counters

below)

to the correct division ratio. Mathematically, this is

(6) 81.25 MHz Mixer. The 100.75 MHz signal

necessary because a dial setting of zero requires

from the 100.75 MHz bandpass filter ((5) above) is

1A4A4U3 to divide by zero-an impossible operation.

mixed with the 19.4001 to 19.50 MHz signal from

The count is corrected by programming 1A4A4U3 to

1A4A3U3 ((3) above) in 81.25 MHz mixer 1A4A3Q11.

divide-by-ten and then subtracting one count from the

The difference frequency output is filtered by the 81.25

next decade counter. Note that this is the same

MHz bandpass filter and applied to output mixer

mathematical operation of borrowing when, for example,

1A4A3Q4 ((7) below).

one subtracts nine from ten. Quad two input NAND gate

(7) Output Mixer. The 81.25 to 81.3499 MHz

1A4A4U4 is connected as a quad inverter with a

signal from the 81.25 MHz bandpass filter ((6) above) is

common output. One of the four 100 kHz input lines is

mixed with the 91.25 to 121.2499 MHz signal from VCO

connected to each section of the gate. The output of

1A4A5 (e below). The frequency of the 81.25 to

1A4A4U4 is inverted by 1A4A4U5A. If all four inputs to

1A4A4U4 are zero, the output of 1A4A4U4 will be in a

81.3499 MHz signal represents the setting of the

one state and the 1A4A4U5A output will be a zero. If

selected 10 kHz, 1 kHz and 100 HZ FREQUENCY

any of the 100 kHz inputs are in a one state, the

switches. The frequency of the 91.25 to 121.2499 MHz

1A4A4U5A output will also be a one.

signal represents the setting of all of the selected

FREQUENCY switches. Since the 10 kHz, 1 kHz and

100 Hz frequency components are present in both

filled detector 1A4A4U8C, 1A4A4U9 are similar to the

signals, they will cancel in the output mixer when the

inputs to count filled detector 1A4A3U3 described in

output of the synthesizer is at the correct frequency

b(3)(e) above. However, the input at pin 5 will always

(normal operating condition). Therefore, the signal from

be high if the selected 100 kHz FREQUENCY switch is

output mixer 1A4A3Q4 will only represent the setting of

set to zero. If the selected 100 kHz FREQUENCY

the selected 10 MHz, 1MHz and 100 kHz FREQUENCY

switch is set to a number other than zero, the input at

switches, and will change in 100 kHz steps. The 10.0 to

pin 5 will follow the output at pins 5 and 6 of 1A4A4U6.

39.9 MHz difference frequency signal from output mixer

The output from the count filled detector is a 400

1A4A3Q4 is amplified by the broadband amplifier and

nanosecond positive pulse.

applied to VHF divider 1A4A4 (d below).

(d) Preset Generator.

Preset generator 11

5A4A4U10 provides a 200 nanosecond negative data

2-13