Publication: Magyar Közlöny
Issue: MK-2007-70 (Year: 2007, Number: 70)
Era: 2004-2010
Section: Melléklet a 2007. évi XLVI. törvényhez
Paragraph Index: 4579

b) at a level lower than 9 dB below the radiated amplitude of P6 within the desired arc of interrogation. 3.1.2.2 REPLY SIGNALS-IN-SPACE CHARACTERISTICS 3.1.2.2.1 Reply carrier frequency. The carrier frequency of all replies (downlink transmissions) from transponders with Mode S capabilities shall be 1 090 plus or minus 1 MHz. 3.1.2.2.2 Reply spectrum. The spectrum of a Mode S reply about the carrier frequency shall not exceed the limits specified in Figure 3-5. 3.1.2.2.3 Polarization. Polarization of the reply transmissions shall be nominally vertical. 3.1.2.2.4 Modulation. The Mode S reply shall consist of a preamble and a data block. The preamble shall be a 4pulse sequence and the data block shall be binary pulse-position modulated at a 1 megabit per second data rate. 3.1.2.2.4.1 Pulse shapes. Pulse shapes shall be as defined in Table 3-2. All values are in microseconds. 3.1.2.2.5 Mode S reply. The Mode S reply shall be as shown in Figure 3-6. The data block in Mode S replies shall consist of either 56 or 112 information bits. 3.1.2.2.5.1 Pulse intervals. All reply pulses shall start at a defined multiple of 0.5 microsecond from the first transmitted pulse. The tolerance in all cases shall be plus or minus 0.05 microsecond. 3.1.2.2.5.1.1 Reply preamble. The preamble shall consist of four pulses, each with a duration of 0.5 microsecond. The pulse intervals from the first transmitted pulse to the second, third and fourth transmitted pulses shall be 1, 3.5 and 4.5 microseconds, respectively. 3.1.2.2.5.1.2 Reply data pulses. The reply data block shall begin 8 microseconds after the leading edge of the first transmitted pulse. Either 56 or 112 one-microsecond bit intervals shall be assigned to each transmission. A 0.5microsecond pulse shall be transmitted either in the first or in the second half of each interval. When a pulse transmitted in the second half of one interval is followed by another pulse transmitted in the first half of the next interval, the two pulses merge and a one-microsecond pulse shall be transmitted. 3.1.2.2.5.2 Pulse amplitudes. The pulse amplitude variation between one pulse and any other pulse in a Mode S reply shall not exceed 2 dB. 2007/70/II. szám Chapter 3 Annex 10 — Aeronautical Telecommunications 3-13 28/11/02 Figure 3-5. Required spectrum limits for transponder transmitter Note.— This figure shows the spectrum centred on the carrier frequency and will therefore shift in its entirety plus or minus 1 MHz along with the carrier frequency. 23 MHz 23 MHz 78 MHz 78 MHz 7 MHz 7 MHz Carrier frequency 1.3 MHz 1.3 MHz 0 dB -3 dB -20 dB -40 dB -60 dB 2007/70/II. szám Annex 10 — Aeronautical Telecommunications Volume IV 28/11/02 3-14 Table 3-2. Pulse shapes — Mode S replies Figure 3-6. Mode S reply 3.1.2.3 MODE S DATA STRUCTURE 3.1.2.3.1 DATA ENCODING 3.1.2.3.1.1 Interrogation data. The interrogation data block shall consist of the sequence of 56 or 112 data chips positioned after the data phase reversals within P6 (3.1.2.1.5.2.3). A 180-degree carrier phase reversal preceding a chip shall characterize that chip as a binary ONE. The absence of a preceding phase reversal shall denote a binary ZERO. 3.1.2.3.1.2 Reply data. The reply data block shall consist of 56 or 112 data bits formed by binary pulse position modulation encoding of the reply data as described in 3.1.2.2.5.1.2. A pulse transmitted in the first half of the interval shall represent a binary ONE whereas a pulse transmitted in the second half shall represent a binary ZERO. 3.1.2.3.1.3 Bit numbering. The bits shall be numbered in the order of their transmission, beginning with bit 1. Unless otherwise stated, numerical values encoded by groups (fields) of bits shall be encoded using positive binary notation and the first bit transmitted shall be the most significant bit (MSB). Information shall be coded in fields which consist of at least one bit. Note.— In the description of Mode S formats the decimal equivalent of the binary code formed by the bit sequence within a field is used as the designator of the field function or command. Pulse duration Duration tolerance (Rise time) (Decay time) Min. Max. Min. Max. 0.5 ±0.05 0.05 0.1 0.05 0.2 1.0 ±0.05 0.05 0.1 0.05 0.2 Preamble 8.0 s m Data block 56 or 112 s m Bit 1 Bit 2 Bit 3 Bit4 Bit N-1 Bit N 1 0 1 0 1 0 1 0 1 0 1 0 8.0 9.0 4.5 3.5 Time ( s) m 0.0 1.0 0.5 Example.— Reply data block corresponding to bit sequence 2007/70/II. szám Chapter 3 Annex 10 — Aeronautical Telecommunications 3-15 28/11/02 3.1.2.3.2 FORMATS OF MODE S INTERROGATIONS AND REPLIES Note.— A summary of all Mode S interrogation and reply formats is presented in Figures 3-7 and 3-8. A summary of all fields appearing in uplink and downlink formats is given in Table 3-3 and a summary of all subfields is given in Table 3-4. 3.1.2.3.2.1 Essential fields. Every Mode S transmission shall contain two essential fields. One is a descriptor which shall uniquely define the format of the transmission. This shall appear at the beginning of the transmission for all formats. The descriptors are designated by the UF (uplink format) or DF (downlink format) fields. The second essential field shall be a 24-bit field appearing at the end of each transmission and shall contain parity information. In all uplink and in currently defined downlink formats parity information shall be overlaid either on the aircraft address (3.1.2.4.1.2.3.1) or on the interrogator identifier according to 3.1.2.3.3.2. The designators are AP (address/parity) or PI (parity/interrogator identifier). Note.— The remaining coding space is used to transmit the mission fields. For specific functions, a specific set of mission fields is prescribed. Mode S mission fields have two-letter designators. Subfields may appear within mission fields. Mode S subfields are labelled with three-letter designators. 3.1.2.3.2.1.1 UF: Uplink format. This uplink format field (5 bits long except in format 24 where it is 2 bits long) shall serve as the uplink format descriptor in all Mode S interrogations and shall be coded according to Figure 3-7. 3.1.2.3.2.1.2 DF: Downlink format. This downlink format field (5 bits long except in format 24 where it is 2 bits long) shall serve as the downlink format descriptor in all Mode S replies and shall be coded according to Figure 3-8. 3.1.2.3.2.1.3 AP: Address/parity. This 24-bit (33-56 or 89-112) field shall appear in all uplink and currently defined downlink formats except the Mode S-only all-call reply, DF = 11. The field shall contain parity overlaid on the aircraft address according to 3.1.2.3.3.2. 3.1.2.3.2.1.4 PI: Parity/interrogator identifier. This 24-bit (33-56) or (89-112) downlink field shall have parity overlaid on the interrogator’s identity code according to 3.1.2.3.3.2 and shall appear in the Mode S all-call reply, DF = 11 and in the extended squitter, DF = 17 or DF = 18. If the reply is made in response to a Mode A/C/S all-call, a Mode S-only all-call with CL field (3.1.2.5.2.1.3) and IC field (3.1.2.5.2.1.2) equal to 0, or is an acquisition or an extended squitter (3.1.2.8.5, 3.1.2.8.6 or 3.1.2.8.7), the II and the SI codes shall be 0. 3.1.2.3.2.2 Unassigned coding space. Unassigned coding space shall contain all ZEROs as transmitted by interrogators and transponders. Note.— Certain coding space indicated as unassigned in this section is reserved for other applications such as ACAS, data link, etc. 3.1.2.3.2.3 Zero and unassigned codes. A zero code assignment in all defined fields shall indicate that no action is required by the field. In addition, codes not assigned within the fields shall indicate that no action is required. Note.— The provisions of 3.1.2.3.2.2 and 3.1.2.3.2.3 ensure that future assignments of previously unassigned coding space will not result in ambiguity. That is, Mode S equipment in which the new coding has not been implemented will clearly indicate that no information is being transmitted in newly assigned coding space. 3.1.2.3.3 ERROR PROTECTION 3.1.2.3.3.1 Technique. Parity check coding shall be used within Mode S interrogations and replies to provide protection against the occurrence of errors. 3.1.2.3.3.1.1 Parity check sequence. A sequence of 24 parity check bits shall be generated by the rule described in 3.1.2.3.3.1.2 and shall be incorporated into the field formed by the last 24 bits of all Mode S transmissions. The 24 parity check bits shall be combined with either the address coding or the interrogator identifier coding as described in 3.1.2.3.3.2. The resulting combination then forms either the AP (address/parity, 3.1.2.3.2.1.3) field or the PI (parity/interrogator identifier, 3.1.2.3.2.1.4) field. 2007/70/II. szám Annex 10 — Aeronautical Telecommunications Volume IV 28/11/02 3-16 NOTES: 1. denotes a field designated “XX” which is assigned M bits. 2. denotes unassigned coding space with N available bits. These shall be coded as ZEROs for transmission.

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