MODE-3 AND MODE-TEST EMERGENCY

TM 11-4920-296-14&P

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to clear all register stages. Basically, this

CAUTION

actions ends the decode-cycle. PRF circuits

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within the U3 module will determine when the

Use only the cable provided; use

next encode-cycle (interrogation) is to begin,

of other cables may result in

and will at that time change the CLOCK rate

damage to the AN/APM-378.

to 1 MHz and generate a P1 pulse on the DATA

Additionally, during M4 operation, the front

line (at U3-TP1), to start the next encode-

panel FUNCTION switch is placed in the

cycle. Encode (Interrogation) and decode

SYSTEM position, and the MODE switch is

(reply) cycles and actions then repeat, in the

set for MODE 4. During M4 Operation, the

manner described thus far for one encode/

CLOCK rate in the test set is 555 kHz (1.8-

decode cycle. The PRF circuits of U3 control

microsecond period). In the same manner

the rate of encode/decode repetition such

as for the SIF modes discussed previously,

that iterrogation/reply-checking occurs at

the encode-cycle of operation begins with a

a rate of 257 cycles per second.

counted-down CLOCK signal generating the

2-34. Each time a correct reply is obtained

To Pulses (U2-TP4). This action sends the

from the transponderundertest, the result-

M4 PRETRIGGER to the KIR-1A, which then

ing SIF GO strobe is fed to the evaluator U4

returns the M4 VIDEO interrogation word.

circuits, as mentioned. An integrator/

The M4 VIDEO pulses are shaped in U4 cir-

comparator circuit of U4 measures the per-

cuits, and are then sent to the U2 circuits

centage of times that correct replies are

(U2-TP10). From U2, the pulses are ap-

received (for the number of times the trans-

plied as Interrogation pulses (U2-TP8) to

ponder is interrogated), and causes the

the rf module to modulate the 1030-MHz

ACCEPT lamp to light. if the correct-reply

t r a n s m i t t e r stages.

rate is greater than 80 percent of the inter-

2-37. In response to the M4 PRETRIGGER,

rogation rate. The 80-percent correct-

the KIR-lA equipment also applies an M4

reply criteria applies for testing of single-

channel and diversity transponders. When

GTC signal to the test set. This signal trig-

gers an approximately 78-microsecond gate

testing lobing-type transponders, a lower

to yield a GTC GO signal (U3-TP9), which in

threshold voltage is applied to the U4 com-

turn provides a VIDEO GATE (U3-TP3) that

parator circuit, to cause the ACCEPT indi-

cation to be indicated for correct-reply

enables a 3-pulse decoder in the U4 module.

rates greater than 40 percent of the inter-

2-38. As for SIG mode operation, the trans-

rogation rate.

mitter rf pulses during the encode-cycle

2-35. MODE-3 AND MODE-TEST EMER-

cause the transponder under test (and its

GENCY. Operation of the test set circuits

associated Interrogator Computer equipment)

for Mode-3 and Mode-Test Emergency is

to generate reply pulses, These reply pulses

similar to that described for the SIF modes.

are checked for correct power and frequency

in the rf module circuits, and if correct, are

However, for these M3 and MT Emergency

operations, the code is always 7700. The

detected and sent as the REPLY SAMPLE

proper comparison code states for the par-

data to the digital section (U3-TP10). Upon

ity comparison are then generated by the

receipt of the REPLY SAMPLE data, CLOCK

A&B ENABLE Ul-TP9) and the C&D) DIS-

is desynchronized and the data is loaded into

ABLE code selector (which bypasses the

shift-register stages. At this time, the 3-

front panel CODE SELECT switches). In

pulse decoder that was enabled in response

Mode C, there is no emergency function. Also,

to the GTC GO signal (U3-TP9) checks for

in Mode C, the test set will give an ACCEPT

coincidence of To (U2-.TP4), the 1-micro-

indication, either with or without a SPI pulse.

second tap signal (U2-TP2), and the 2-micro-

second tap signal (U4-TP2). If correct coin-

2-36. MODE-4 OPERATION. For Mode-4

dence occurs for this check, a pulse is

applied to one input of an AND circuit of U4.

(M4) operation, the test set is used in

conjunction with an Interrogator Computer

2-39. The REPLY SAMPLE data, after

KIR-1A. The KH3-1A is connected to the

test set via the M4 cable supplied with

regeneration, is also applied to the KIR-lA

the test set.

Interrogator Computer as the M4 REPLY

2-11