User's Manual

ROCKWELL COLLINS
COMPONENT MAINTENANCE MA NUAL with IPL
TDR-94, PART NO 622-9352
ATCRBS Interrogator Pulse
Figure 6/G RAPHIC 34-50-96-99B-073-A01
(3) ATC Transponder Replies
(a) As mentioned ear lier, the most common transponder modes are mode A and mode
C. Mode A provides ident (identification) information, w hile mode C provides altitude
data. Th
e reply for mats are very similar, differ ing only in pulse spacing (delay).
(b) The ATCR BS mode A transponder reply signal is shown in Figure 7/GRAPHIC
34-50-
96-99B-074-A01. Notice that the signal can consist of from 2 to 16 pulses.
The two framing pulses F1 and F2 are always present and spaced 20.3 μs. An
identification pulse may be transmitted 4.35 μs after the last framing pulse F2. The
interv
ening pulses, A1 through D4, make up the coded reply. The X pulse is not
used. The coded reply consists of twelve pulses; four groupings of three pulses
each. These groupings give four digits of octal data. The digits are formed by
the su
m of the pulse (bit) values; 1, 2, or 4, which can produce a digit value from
0 through 7. The A group (A1, A2, and A4) makes up the first digit, the B group
makes up the second digit, etc. (On the figure, a pulse outlined w ith a s olid line
indi
cates that the pulse is present. A pulse outlined with dashed lines indicates the
position for that pulse when it is present.) The pulse configuration on the figure
indicates a reply code 1324. The first digit, 1, is formed by the presence of only the
A1 pu
lse. The second digit, 3, is formed by the presence of B1 and B2 (1 + 2 =
3). A digit 7 is formed when all three pulses of the group are present (1 + 2 + 4 =
34-50-96
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May 18/06