Section 171.311 14 CFR Ch. I (1-1-19 Edition) (i) Digital codes. The coding used in the preamble for receiver synchronization is a Barker code logic 11101. The time of the last phase transition midpoint in the code shall be the receiver reference time (see Table 2). The function identification codes must be as shown in Table 3. The last two bits (I11 and I12) of the code are parity bits obeying the equations: TABLE 2 - PREAMBLE TIMING 1 - Continued Event time slot begins at - Event END PREAMBLE ................. 1.600 for all function Code Function TABLE 2 - PREAMBLE TIMING 1 Event time slot begins at - Carrier acquisition: (CW transmission) ............... Receiver reference time code: I1 = 1 .................................... I2 = 1 .................................... I3 = 1 .................................... I4 = 0 .................................... I5 = 1 .................................... Function identification: I6 ........................................... I7 ........................................... I8 ........................................... I9 ........................................... I10 (see table 1) .................... I11 ......................................... I12 ......................................... 25 1 Applies to all functions transmitted. 2 Reference time for receiver synchronization TABLE 3 - FUNCTION IDENTIFICATION CODES (ii) Data modulation. The digital code portions of the preamble must be DPSK modulated in accordance with Section 171.311(c)(1) and must be transmitted throughout the function coverage volume. (2) Angle function formats. The timing of the angle transmissions must be in accordance with Tables 4a, 4b, and 5. The actual timing of the TO and FRO scans must be as required to meet the accuracy requirements of SectionSection 171.313 and 171.317. (i) Preamble. Must be in accordance with requirements of Section 171.311(i)(1). 15.625 kHz clock pulse (number) Time (milliseconds) timing. I6 + I7 + I8 + I9 + I10 + I11 = Even I6 + I8 + I10 + I12 = Even Event 15.625 kHz clock pulse (number) Time (milliseconds) 0 0 13 14 15 16 17 0.832 0.896 0.960 1.024 2 1.088 18 19 20 21 22 23 24 1.152 1.216 1.280 1.344 1.408 1.472 1.536 Approach azimuth .................... High rate approach azimuth ..... Approach elevation .................. Back azimuth ............................ Basic data 1 ............................. Basic data 2 ............................. Basic data 3 ............................. Basic data 4 ............................. Basic data 5 ............................. Dasic data 6 ............................. Auxiliary data A ........................ Auxiliary data B ........................ Auxiliary data C ........................ I6 I7 I8 I9 I10 I11 I12 0 0 1 1 0 0 1 1 1 0 1 1 1 0 0 1 0 1 1 0 0 1 0 1 0 1 1 1 0 0 0 1 1 0 0 0 1 1 1 1 0 0 1 1 1 0 0 1 1 0 0 1 0 1 0 0 0 1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 0 1 1 0 0 0 0 0 1 0 1 0 (ii) Sector signals. In all azimuth formats, sector signals must be transmitted to provide Morse Code identification, airborne antenna selection, and system test signals. These signals are not required in the elevation formats. In addition, if the signal from an installed ground component results in a valid indication in an area where no valid guidance should exist, OCI signals must be radiated as provided for in the signal format (see Tables 4a, 4b, and 5). The sector signals are defined as follows: (A) Morse Code. DPSK transmissions that will permit Morse Code facility identification in the aircraft by a four letter code starting with the letter - M - must be included in all azimuth functions. They must be transmitted and repeated at approximately equal intervals, not less than six times per VerDate Sep<11>2014 08:20 May 17, 2019 Jkt 247048 PO 00000 Frm 00864 Fmt 8010 Sfmt 8010 Y:\SGML\247048.XXX 247048 EC15SE91.010 854