Receiver Section

TM 11-6625-667-45/NAVAIR 16-30APM123-2/TO 33A1-3-367-22

prf periods, and provides the accept or reject

2-4. Receiver Section

readout o

(fig. 8-1)

Test

The receiver section evaluates the transponder set

System:

replies for proper frequency and power level. It

Mode 1------ Any combination of A1, A2, A4, B1,

consists of preselector A15Z1, detector A15Z2, a

and B2 plus framing pulses. Other

information pulse not present.

video amplifier, video switching and receiver gates,

Mode 2------ Any combination of all information

video shaper DSS1, mode 4 shaper DSS6, and an

pulses plus framing pulse.

emitter follower. The receiver frequency is 1,090

Mode 3/A---- Any combination of all information

mc 0.5, and the bandwidth at the 3-db points

pulses plus framing pulses.

of the selectivity curve is 6.5 mc 1. The receiver

Mode C------ Any combination of all information

sensitivity is adjustable between 15 and 0 dbm.

pulses, except for 500 feet incre-

ments (combinations of A1, A2,

It is normally preadjusted to 9 dbm 1 for test-

A4, B1, B2, B4, D2, D4, and I/P

ing transponder that have a minimum transmitter

are used) and 100 feat increments

power level of +48 dbm. The receiver sensitivity

(combinations of A1, A2, A4, B1,

can be preadjusted internally ( 15 to 0 dbm) to

B2, B4, C1, C2, C4, and D2 are

plus framing pulses.

used)

test minimum RF levels between +42 and +57

Identity:

dbm. Transponder replies that have the proper

Any combination of all information

Mode 2 and

frequency and RF levels are detected and will suf-

3/A.

pulses plus the I/P pulse and

ficiently drive the video amplifier. The video am-

framing pulse.

Mode 1------ Two trains of any combination of all

plifier output is gated to trigger video shaper

information pulses plus framing

DSS1 during all test except mode 4. During

pulses.

mode 4 tests the video is gated to external equip-

Emergency:

ment. The receiver video gates are enabled as de-

Mode 1 and 2- Any combination of all information

scribed in paragraph 2-5a by the decoder section,

pulses plus three sets of framing

pulses.

and receiver gate periods are described in para-

Mode 3/A---- A1, A2, A4, B1, B2, and B4 plus

graph 2-5c.

three sets of framing pulses.

2-5. Decoder Section

b. Receiver Gating. Refer to figures 2-3 through

2-6 for the timing diagrams. The receiver gating

a. General. The decoder section (fig. 8-1) evalu-

operation is started by the decode enable pulse

ates the transponder reply video for all tests ex-

cept mode 4. It detects the presence and position

produced by the last (P3) interrogation pulse

of each pulse in a reply train. Figure 2-2 illus-

(para 2-2b). Video enable DFF6 is reset and video

trate the basic train, and the position of the

enable delay DSS4 is triggered by this pulse. In

identity pulse or a second F1 framing pulse. The

the reset state, DFF6 disables the receiver video

various types of replies expected in system tests,

gates. When triggered, DSS4 produces a 1.8-micro-

identity tests and emergency tests are listed in the

second positive pulse. The trailing edge of the

chart below. Since the test set, does not evaluate the

pulse sets DFF6, which in turn enables the receiver

mode 4 reply, its format is not illustrated. Framing

video gates and comparator pulse generator out-

and information pulses are evaluated for the

put. Thus, reply can be gated to video shaper

DSS1 (para 2-4) 1.8 0.1 microsecond after the

following spacing variations; those within 0.15-

microsecond of the nominal are accepted; those

last interrogation pulse is produced. The gate pe-

deviating greater than 0.35 microsecond from

riod depends on the mode and function used in a

the nominal are rejected. Extra pulses or the ab-

test. Video enable DFF6 is reset by the video en-

able reset switching and gating circuits (d below).

sence of an expected pulse will also cause a re-

The output of video enable delay DSS4 also

ject condition. To perform this evaluation, the

triggers read delay DSS5 (c below). Encircled

decoder section enables the receiver gate, gen-

erates a comparison pulse train, detects the quan-

numbers in the timing diagrams (figs. 2-3 through

tity of correct replies within approximately 50

2-6) indicate a new start.

2-4

Change 3