Annex 10 — Aeronautical Telecommunications Volume IV
28/11/02 3-6
3.1.1.7.8 Random triggering rate. In the absence of valid interrogation signals, Mode A/C transponders shall not
generate more than 30 unwanted Mode A or Mode C replies per second as integrated over an interval equivalent to at least
300 random triggers, or 30 seconds, whichever is less. This random triggering rate shall not be exceeded when all possible
interfering equipments installed in the same aircraft are operating at maximum interference levels.
3.1.1.7.9 R
EPLY
RATE
3.1.1.7.9.1 The transponder shall be capable of at least 1 200 replies per second for a 15-pulse coded reply, except
that, for transponder installations used solely below 4 500 m (15 000 ft), or below a lesser altitude established by the
appropriate authority or by regional air navigation agreement, transponders capable of at least 1 000 replies per second
for a 15-pulse coded reply shall be permitted.
3.1.1.7.9.2 Reply rate limit control. To protect the system from the effects of transponder over-interrogation by
preventing response to weaker signals when a predetermined reply rate has been reached, a sensitivity reduction type reply
limit control shall be incorporated in the equipment. The range of this control shall permit adjustment, as a minimum, to
any value between 500 and 2 000 replies per second, or to the maximum reply rate capability if less than 2 000 replies
per second, without regard to the number of pulses in each reply. Sensitivity reduction in excess of 3 dB shall not take
effect until 90 per cent of the selected value is exceeded. Sensitivity reduction shall be at least 30 dB for rates in excess
of 150 per cent of the selected value.
3.1.1.7.9.3 Recommendation.— The reply rate limit should be set at 1 200 replies per second, or the maximum value
below 1 200 replies per second of which the transponder is capable.
3.1.1.7.10 Reply delay and jitter. The time delay between the arrival, at the transponder receiver, of the leading edge
of P
3
and the transmission of the leading edge of the first pulse of the reply shall be 3 plus or minus 0.5 microseconds.
The total jitter of the reply pulse code group, with respect to P
3
, shall not exceed 0.1 microsecond for receiver input levels
between 3 dB and 50 dB above minimum triggering level. Delay variations between modes on which the transponder is
capable of replying shall not exceed 0.2 microsecond.
3.1.1.7.11 T
RANSPONDER
POWER
OUTPUT
AND
DUTY
CYCLE
3.1.1.7.11.1 The peak pulse power available at the antenna end of the transmission line of the transponder shall be
at least 21 dB and not more than 27 dB above 1 W, except that for transponder installations used solely below 4 500 m
(15 000 ft), or below a lesser altitude established by the appropriate authority or by regional air navigation agreement, a
peak pulse power available at the antenna end of the transmission line of the transponder of at least 18.5 dB and not more
than 27 dB above 1 W shall be permitted.
3.1.1.7.11.2 Recommendation.— The peak pulse power specified in 3.1.1.7.11.1 should be maintained over a range
of replies from code 0000 at a rate of 400 replies per second to a maximum pulse content at a rate of 1 200 replies per
second or a maximum value below 1 200 replies per second of which the transponder is capable.
3.1.1.7.12 R
EPLY
CODES
3.1.1.7.12.1 Identification. The reply to a Mode A interrogation shall consist of the two framing pulses specified in
3.1.1.6.1 together with the information pulses (Mode A code) specified in 3.1.1.6.2.
Note.— The Mode A code designation is a sequence of four digits in accordance with 3.1.1.6.6.
3.1.1.7.12.1.1 The Mode A code shall be manually selected from the 4 096 codes available.
3.1.1.7.12.2 Pressure-altitude transmission. The reply to Mode C interrogation shall consist of the two framing pulses
specified in 3.1.1.6.1 above. When digitized pressure-altitude information is available, the information pulses specified in
3.1.1.6.2 shall also be transmitted.
3.1.1.7.12.2.1 Transponders shall be provided with means to remove the information pulses but to retain the framing
pulses when the provision of 3.1.1.7.12.2.4 below is not complied with in reply to Mode C interrogation.