RECEIVER CONTROL 1A4A2

TM 11-5820-917-13

4-93. RECEIVER CONTROL 1A4A2 (figure FO-38). The receiver control assembly

can be divided into five functional circuits: front panel select, preselector decode,

frequency counter, cursor-to-frequency converter, and auto start.

4-94. FRONT PANEL SELECT (figure FO-38/1). This circuit interfaces all subpanel

switches with related parts of the receiver control circuits. All pushbutton

switches are debounced and rotary switch positions routed to relevant circuitry at

the proper time.

4-95. PRESELECTOR DECODE (figure FO-38/2). Binary-coded-decimal (BCD) fre-

quency data is routed from the local oscillator (LO) frequency counter (paragraph

4-96) to the preselector decode circuit, for translation to frequency range data

for the receiver preselect filters. The frequency information is decoded to pro-

vide a 1 of 8 selection (negative true output) to drive the preselector switches as

follows :

OUTPUT (LOW)

FREQUENCY

RANGE

PRE

2.0-

3.0 MHz

PRE

3.0-

4.4

PRE

4.4-

6.0

PRE

6.0-

8.4

PRE

8.4-

12.0

PRE

12.0 -

17.0

PRE

17.0-

24.0

PRE

24.0-

30.0

4-96. FREQUENCY COUNTER (figure FO-38/3). This circuit counts the 2-3.5 MHz

frequency from the synthesizer and provides BCD frequency information to the

LED display and preselector decode. The 2-3.5 MHz input is gated into U13 for

two milliseconds. Counters U9-U13 are preset with the number 5980. During

the two millisecond gate interval, U9-U13 count up from 5980. At the end of the

two-millisecond period, the number contained in the counters is the actual re-

ceived frequency (disregarding the carry digit) . For example, at 2 MHz, the re-

ceiver synthesizer frequency is 42.2 MHz. The frequency counter counts every

20th cycle, or 2,110 counts/millisecond. Thus, 4,220 counts are gated for two

milliseconds:

Gate for 2 milliseconds = 4220

add counter preset

= 5980

10200

Disregard carry

For

02.00 MHz (receiver frequency)

The BCD frequency information is routed through U17-U20 which form a 16-pole,

double-throw switch. This switch is in turn activated by the front panel Cursor/

RCVR pushbutton, which in the normal (RCVR) position switches the BCD infor-

mation into the LED display.

4-97. CURSOR TO FREQUENCY CONVERTER (figure FO-38/3). The cursor storage

and readout assemblv (1A2A1) sends information (signal CUL) to the cursor to

frequency converter logic indicating the frequency on which the movable cursor

4-40