Publication: Magyar Közlöny
Issue: MK-2009-104 (Year: 2009, Number: 104)
Era: 2004-2010
Section: 
Paragraph Index: 2332

b) at all signal levels between MTL +3 dB and –21 dBm, have a reply ratio of at least 99 per cent if the received amplitude of P6 exceeds the received amplitude of P5 by 12 dB or more. 3.1.2.10.3.2 Mode S dead time. Dead time shall be defined as the time interval beginning at the end of a reply transmission and ending when the transponder has regained sensitivity to within 3 dB of MTL. Mode S transponders shall not have more than 125 microseconds’ dead time. 3.1.2.10.3.3 Mode S receiver desensitization. The transponder’s receiver shall be desensitized according to 3.1.1.7.7.1 on receipt of any pulse of more than 0.7 microseconds duration. 3.1.2.10.3.3.1 Recovery from desensitization. Recovery from desensitization shall begin at the trailing edge of each pulse of a received signal and shall occur at the rate prescribed in 3.1.1.7.7.2, provided that no reply or data transfer is made in response to the received signal. 3.1.2.10.3.4 Recovery after Mode S interrogations that do not elicit replies 3.1.2.10.3.4.1 Recovery after a single Mode S interrogation 3.1.2.10.3.4.1.1 The transponder shall recover sensitivity to within 3 dB of MTL no later than 128 microseconds after receipt of the sync phase reversal following a Mode S interrogation that is not accepted (3.1.2.4.1.2) or that is accepted but requires no reply. 3.1.2.10.3.4.1.2 Recommendation.— The transponder should recover sensitivity to within 3 dB of MTL no later than 45 microseconds after receipt of the sync phase reversal following a Mode S interrogation that is not accepted (3.1.2.4.1.2) or that is accepted but requires no reply. 3.1.2.10.3.4.1.3 All Mode S transponders installed on or after 1 January 1999 shall recover sensitivity to within 3 dB of MTL no later than 45 microseconds after receipt of the sync phase reversal following a Mode S interrogation that is not accepted (3.1.2.4.1.2) or that is accepted but requires no reply. 3.1.2.10.3.4.2 Recovery after a Mode S Comm-C interrogation. A Mode S transponder with Comm-C capability shall recover sensitivity to within 3 dB of MTL no later than 45 microseconds after receipt of the sync phase reversal following acceptance of a Comm-C interrogation for which no reply is required. 3.1.2.10.3.5 Unwanted Mode S replies. Mode S transponders shall not generate unwanted Mode S replies more often than once in 10 seconds. Installation in the aircraft shall be made in such a manner that this standard shall be achieved when all possible interfering equipments installed in the same aircraft are operating at maximum interference levels. 3.1.2.10.3.5.1 Unwanted Mode S replies in the presence of low-level in-band CW interference. In the presence of non-coherent CW interference at a frequency of 1 030 ±0.2 MHz and at signal levels of -60 dBm or less, and in the absence of valid interrogation signals, Mode S transponders shall not generate unwanted Mode S replies more often than once per 10 seconds. 3.1.2.10.3.6 Reply rate limiting Note.— Reply rate limiting is prescribed separately for Modes A and C and for Mode S. 3.1.2.10.3.6.1 Mode S reply rate limiting. Reply rate limiting is not required for the Mode S formats of a transponder. If such limiting is incorporated for circuit protection, it shall permit the minimum reply rates required in 3.1.2.10.3.7.2 and 3.1.2.10.3.7.3. Annex 10 — Aeronautical Telecommunications Volume IV 22/11/07 3-64 3.1.2.10.3.6.2 Modes A and C reply rate limiting. Reply rate limiting for Modes A and C shall be effected according to 3.1.1.7.9.1. The prescribed sensitivity reduction (3.1.1.7.9.2) shall not affect the Mode S performance of the transponder. 3.1.2.10.3.7 Minimum reply rate capability, Modes A, C and S 3.1.2.10.3.7.1 All reply rates specified in 3.1.2.10.3.7 shall be in addition to any squitter transmissions that the transponder is required to make. 3.1.2.10.3.7.2 Minimum reply rate capability, Modes A and C. The minimum reply rate capability for Modes A and C shall be in accordance with 3.1.1.7.9. 3.1.2.10.3.7.3 Minimum reply rate capability, Mode S. A transponder capable of transmitting only short Mode S replies shall be able to generate replies at the following rates: 50 Mode S replies in any 1-second interval 18 Mode S replies in a 100-millisecond interval 8 Mode S replies in a 25-millisecond interval 4 Mode S replies in a 1.6-millisecond interval In addition to any downlink ELM transmissions, a level 2, 3 or 4 transponder shall be able to generate as long replies at least: 16 of 50 Mode S replies in any 1-second interval 6 of 18 Mode S replies in a 100-millisecond interval 4 of 8 Mode S replies in a 25-millisecond interval 2 of 4 Mode S replies in a 1.6-millisecond interval In addition to downlink ELM transmissions, a level 5 transponder shall be able to generate as long replies at least: 24 of 50 Mode S replies in any 1-second interval 9 of 18 Mode S replies in a 100-millisecond interval 6 of 8 Mode S replies in a 25-millisecond interval 2 of 4 Mode S replies in a 1.6-millisecond interval In addition, a transponder within an ACAS installation shall be able to generate as ACAS coordination replies at least 3 of 50 Mode S replies in any 1-second interval. 3.1.2.10.3.7.4 Minimum Mode S ELM peak reply rate Note 1.— When a downlink ELM is initialized (3.1.2.7.7.1), the Mode S transponder announces the length (in segments) of the waiting message. The transponder must be able to transmit this number of segments, plus an additional margin to make up for missed replies, during the beam dwell of the ground interrogator. At least once every second a Mode S transponder equipped for ELM downlink operation shall be capable of transmitting in a 25-millisecond interval, at least 25 per cent more segments than have been announced in the initialization (3.1.2.7.7.1). The minimum length downlink ELM capability for level 4 and 5 transponders shall be as specified in 3.1.2.10.5.2.2.2. Note 2.— A transponder capable of processing the maximum length downlink ELM (16 segments) is therefore required to be able to transmit 20 long replies under the above conditions. Level 4 transponders may be built which process less than the maximum message length. These transponders cannot initialize a message length that exceeds their transmitter capability. For example, a transponder that can transmit at most 10 long replies under the above conditions can never announce a message of more than 8 segments. Chapter 3 Annex 10 — Aeronautical Telecommunications 3-65 22/11/07 3.1.2.10.3.8 Reply delay and jitter Note.— After an interrogation has been accepted and if a reply is required, this reply transmission begins after a fixed delay needed to carry out the protocols. Different values for this delay are assigned for Modes A and C, for Mode S and for Modes A/C/S all-call replies. 3.1.2.10.3.8.1 Reply delay and jitter for Modes A and C. The reply delay and jitter for Modes A and C transactions shall be as prescribed in 3.1.1.7.10. 3.1.2.10.3.8.2 Reply delay and jitter for Mode S. For all input signal levels between MTL and –21 dBm, the leading edge of the first preamble pulse of the reply (3.1.2.2.5.1.1) shall occur 128 plus or minus 0.25 microsecond after the sync phase reversal (3.1.2.1.5.2.2) of the received P6. The jitter of the reply delay shall not exceed 0.08 microsecond, peak (99.9 percentile). 3.1.2.10.3.8.3 Reply delay and jitter for Modes A/C/S all call. For all input signal levels between MTL +3 dB and –21 dBm the leading edge of the first preamble pulse of the reply (3.1.2.2.5.1.1) shall occur 128 plus or minus 0.5 microseconds after the leading edge of the P4 pulse of the interrogation (3.1.2.1.5.1.1). Jitter shall not exceed 0.1 microsecond, peak (99.9 percentile). Note.— A peak jitter of 0.1 microsecond is consistent with the jitter prescribed in 3.1.1.7.10. 3.1.2.10.3.9 Timers. Duration and features of timers shall be as shown in Table 3-10. All timers shall be capable of being restarted. On receipt of any start command, they shall run for their specified times. This shall occur regardless of whether they are in the running or the non-running state at the time that the start command is received. A command to reset a timer shall cause the timer to stop running and to return to its initial state in preparation for a subsequent start command. 3.1.2.10.3.10 Inhibition of replies. Replies to Mode A/C/S all-call and Mode S-only all-call interrogations shall always be inhibited when the aircraft declares the on-the-ground state. It shall not be possible to inhibit replies to discretely addressed Mode S interrogations regardless of whether the aircraft is airborne or on the ground. 3.1.2.10.3.10.1 Recommendation.— Aircraft should provide means to determine the on-the-ground state automatically and provide that information to the transponder. 3.1.2.10.3.10.2 Recommendation.— Mode A/C replies should be inhibited when the aircraft is on the ground to prevent interference when in close proximity to an interrogator or other aircraft. Note.— Mode S discretely addressed interrogations do not give rise to such interference and may be required for data link communications with aircraft on the airport surface. Acquisition squitter transmissions may be used for passive surveillance of aircraft on the airport surface. 3.1.2.10.3.10.3 Inhibition of squitter transmissions. It shall not be possible to inhibit extended squitter transmissions except as specified in 3.1.2.8.6 or acquisition squitter transmissions except as specified in 3.1.2.8.5 regardless of whether the aircraft is airborne or on the ground. Note.— For additional information on squitter inhibition see the Manual of the Secondary Surveillance Radar (SSR) Systems (Doc 9684). 3.1.2.10.4 Transponder antenna system and diversity operation. Mode S transponders equipped for diversity operation shall have two RF ports for operation with two antennas, one antenna on the top and the other on the bottom of the aircraft’s fuselage. The received signal from one of the antennas shall be selected for acceptance and the reply shall be transmitted from the selected antenna only. Annex 10 — Aeronautical Telecommunications Volume IV 22/11/07 3-66 3.1.2.10.4.1 Radiation pattern. The radiation pattern of Mode S antennas when installed on an aircraft shall be nominally equivalent to that of a quarter-wave monopole on a ground plane. Note.— Transponder antennas designed to increase gain at the expense of vertical beamwidth are undesirable because of their poor performance during turns. 3.1.2.10.4.2 Antenna location. The top and bottom antennas shall be mounted as near as possible to the centre line of the fuselage. Antennas shall be located so as to minimize obstruction to their fields in the horizontal plane. 3.1.2.10.4.2.1 Recommendation.— The horizontal distance between the top and bottom antennas should not be greater than 7.6 m (25 ft). Note.— This recommendation is intended to support the operation of any diversity transponder (including cables) with any diversity antenna installation and still satisfy the requirement of 3.1.2.10.4.5. 3.1.2.10.4.3 Antenna selection. Mode S transponders equipped for diversity operation shall have the capability to evaluate a pulse sequence simultaneously received on both antenna channels to determine individually for each channel if the P1 pulse and the P2 pulse of a Mode S interrogation preamble meet the requirements for a Mode S interrogation as defined in 3.1.2.1 and if the P1 pulse and the P3 pulse of a Mode A, Mode C or intermode interrogation meet the requirements for Mode A and Mode C interrogations as defined in 3.1.1. Note.— Transponders equipped for diversity operation may optionally have the capability to evaluate additional characteristics of the received pulses of the interrogations in making a diversity channel selection. The transponder may as an option evaluate a complete Mode S interrogation simultaneously received on both channels to determine individually for each channel if the interrogation meets the requirements for Mode S interrogation acceptance as defined in 3.1.2.4.1.2.3. 3.1.2.10.4.3.1 If the two channels simultaneously receive at least a P1 – P2 pulse pair that meets the requirements for a Mode S interrogation, or a P1 – P3 pulse pair that meets the requirements for a Mode A or Mode C interrogation, or if the two channels simultaneously accept a complete interrogation, the antenna at which the signal strength is greater shall be selected for the reception of the remainder (if any) of the interrogation and for the transmission of the reply. 3.1.2.10.4.3.2 If only one channel receives a pulse pair that meets the requirements for an interrogation, or if only one channel accepts an interrogation, the antenna associated with that channel shall be selected regardless of received signal strength. 3.1.2.10.4.3.3 Selection threshold. If antenna selection is based on signal level, it shall be carried out at all signal levels between MTL and –21 dBm. Note.— Either antenna may be selected if the difference in signal level is less than 3 dB. 3.1.2.10.4.3.4 Received signal delay tolerance. If an interrogation is received at one antenna 0.125 microsecond or less in advance of reception at the other antenna, the interrogations shall be considered to be simultaneous interrogations, and the above antenna selection criteria applied. If an accepted interrogation is received at either antenna 0.375 microsecond or more in advance of reception at the other antenna, the antenna selected for the reply shall be that which received the earlier interrogation. If the relative time of receipt is between 0.125 and 0.375 microsecond, the transponder shall select the antenna for reply either on the basis of the simultaneous interrogation criteria or on the basis of the earlier time of arrival. 3.1.2.10.4.4 Diversity transmission channel isolation. The peak RF power transmitted from the selected antenna shall exceed the power transmitted from the non-selected antenna by at least 20 dB. 3.1.2.10.4.5 Reply delay of diversity transponders. The total two-way transmission difference in mean reply delay between the two antenna channels (including the differential delay caused by transponder-to-antenna cables and the horizontal distance along the aircraft centre line between the two antennas) shall not exceed 0.13 microsecond for interrogations of equal Chapter 3 Annex 10 — Aeronautical Telecommunications 3-67 22/11/07 amplitude. This requirement shall hold for interrogation signal strengths between MTL +3 dB and –21 dBm. The jitter requirements on each individual channel shall remain as specified for non-diversity transponders. Note.— This requirement limits apparent jitter caused by antenna switching and by cable delay differences. 3.1.2.10.5 DATA PROCESSING AND INTERFACES 3.1.2.10.5.1 Direct data. Direct data shall be those which are required for the surveillance protocol of the Mode S system. 3.1.2.10.5.1.1 Fixed direct data. Fixed direct data are data from the aircraft which do not change in flight and shall be:

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