Sweep/Step Rate Data Generation

TM 11-5865-215-13

Table 5-6.

A/D Data Selection

decimal counter

U12 output

(pin 2)

(pin 1)

(pin 3)

Analog input

Output

(selected by U15)

CLARIFIER

U24A,U24B

MGC

U18A, U18B

SWEEP

UllB

h. Sweep/Step Rate Data Generation. The SWEEP/STEP binary data

output (Q3 thru Q6) from the a/d converter is applied to variable

counter U10 when U11A is strobed by the a/d multiplexer circuits (see

figures 5-9 and FO-11). When the receiver control is in the program-

med step or frequency sweep operation, pressing the front panel START

key produces a momentary low which is applied to the input of NAND

gates U14 and U7. This drives the output of these gates high. The

high presets binary counter U9 with a 15 count, and presets variable

down counter U1O with an N count (N equals the Q3 thru Q6 output from

the a/d converter). Binary counter U9 always counts down from the

preset binary 15 input. As a result, the 2890-Hz input clock (CLOCK B)

is divided by 16, providing a 180-Hz output to U10. This is further

divided by a factor of N by variable down counter U10 to produce the

180-Hz/N output. For example, if U10 is preset with a binary 5 input

(i.e. , Q3 thru Q6 equals 0.012, or N equals 5), the 180-Hz input is

divided by 5. The resulting 36-Hz output is applied to output counter

U 8 . This counter further (divides the input frequency by 2 to provide

the sweep rate. U8 also divides the input by 128 to provide the step

rate.

The divided output (90 Hz/N) is applied to the D2 input of output

input of U1lB, while a 0.28-Hz input (one pulse every 3.56 s.) is

applied to D3. These signals are output to the input port 2 IB22 and

IB23 lines in response to a microprocessor output port 7 OB73 (low)

bit. This information determines the rate at which the receiver fre-

quency changes (when the receiver control. is in the frequency sweep

model, or the step rate at which the programmed receiver commands

change (when the receiver (control is in programmed auto-step mode).

Figure FO-11 lists the a/d converter output (N) and the resulting

sweep and step rates provided in response to the front panel SWEEP

RATE control (analog voltage) input.

The front panel MANUAL TUNING con-

i. Manual Tuning Conversion.

trol is an optical encoder which provides PHASE A and PHASE B output

signals (see figure FO-11). These signals are applied to A-quad-B

5-26