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Page Title:
CHAPTER 5.1 MODE 4 FUNCTIONING AND MAINTENANCE FOR MODE 4 |
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 TM 11-6625-667-45
CHAPTER 5.1
MODE 4 FUNCTIONING AND MAINTENANCE FOR MODE 4
Section I. FUNCTIONING
the test set. The signal consists of a group of
5.1-1. GeneraI
pulses (36 maximum) in response to each pre-
a. The test set performs mode 4 tests when
trigger pulse, and there are four such groups
connected to mode 4 interrogator equipment.
during a test period. The challenge video mod-
A transponder set under test is connected to
ulated RF is transmitted to the transponder set
mode 4 transponder equipment. Test results
by the test set transmitter section.
indicate whether the transponder set and mode
4 equipments are performing correctly. Radia-
c. Mode 4 ISLS pulses are produced in the
tion and direct RF coupling type tests are
mode 4 encoder. When selected, the first mode
4 challenge video pulse causes an ISLS trig-
performed in a manner similar to SIF tests
(modes 1, 2, 3, and C). The test set front pan-
ger forming circuit to produce an ISLS trigger
el MODE 4 switch, RAD-DIR, is set to RAD
p u l s e after 8 microseconds. The resultant
pulse will appear as the fifth pulse of the
for radiation and DIR for direct connection
mode 4 challenge video. Responses from the
tests. Each switch position establishes the con-
transponder to mode 4 challenges are detected
dition necessary for an accept indication. Dur-
and processed by the test set receiver section.
ing SIF tests, 80 percent or more correct re-
The resultant three-pulse reply video is de-
plies provide an accept indication. When mode
4 radiation checks are in progress, 56 or more
coded. When the pulse positions are within es-
tablished limits, a decoded reply video pulse is
correct replies within a 64 pulse recurrence
frequency (prf) evaluation period are required
routed through the MODE 4 jack to the mode
for an accept condition. For mode 4 direct RF
4 interrogation equipment. The mode 4 inter-
coupling tests, 16 consecutive correct replies
rogation equipment returns a time-decoded
video pulse (TVD) to the test set for counting in re-
within the 64 prf evaluation period are re-
quired. When the PUSH TO TEST switch is
sponse to the decoded reply video pulse and a
test ACCEPT or REJECT indication is pro-
depressed, the test begins after approximately
50 prf periods. Testing is not performed on a
duced under the conditions described above.
continuous basis as with SIF tests. A mode 4
indication (ACCEPT or REJECT indicator)
5.1-2. Detailed Functional Analysis
will appear as long as the PUSH TO TEST
a. Mode 4 Decoder Section Challenge Vid-
switch is depressed.
eo Shaping, ISLS Generation, and Reply Eval-
b. When the PUSH TO TEST switch is de-
TO TEST switch is pressed, the mode 4 pre-
pressed, mode 4 pretrigger pulses will be pro-
trigger and prf generator A5Q14/A5Q15 cir-
duced by the encoder in the transmitter section.
cuits are activated. The prf signal is coupled by
These pulses are applied through the MODE
PRF-AMPL A1Q7 to set M4 decode enable
4 jack to the mode 4 interrogation equipment.
A1FF2, thereby enabling ISLS line drive gate
After a delay of time, this equipment returns
A1M8B and enable gate A1M8A. The mode 4
mode 4 challenge video modulation pulses to
pretrigger is directed through the MODE 4
5.1-1
Change 4
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