Section 171.311 14 CFR Ch. I (1-1-19 Edition) fall times shall be less then 10 microseconds. It shall be permissible to sequentially transmit two pulses in each out-of-coverage indication time slot. Where pulse pairs are used, the duration of each pulse shall be at least 50 microseconds, and the rise and fall times shall be less then 10 microseconds. The transmission of out-of-coverage indication pulses radiated from antennas with overlapping coverage patterns shall be separated by at least 10 microseconds. NOTE: If desired, two pulses may be sequentially transmitted in each OCI time slot. Where pulse pairs are used, the duration of each pulse must be 45 (Section5) microseconds and the rise and fall times must be less than 10 microseconds. (D) System test. Time slots are provided in Tables 4a and 4b to allow radiation of TO and FRO test pulses. However, radiation of these pulses is not required since the characteristics of these pulses have not yet been standardized. (iii) Angle encoding. The encoding must be as follows: (A) General. Azimuth and elevation angles are encoded by scanning a narrow beam between the limits of the proportional coverage sector first in one direction (the TO scan) and then in the opposite direction (the FRO scan). Angular information must be encoded by the amount of time separation between the beam centers of the TO and FRO scanning beam pulses. The TO and FRO transmissions must be symmetrically disposed about the midscan point listed in Tables 4a, 4b, 5, and 7. The midscan point and the center of the time interval between the TO and FRO scan transmissions must coincide with a tolerance of Section10 microseconds. Angular coding must be linear with angle and properly decoded using the formula: = V 2 (T0 - t ) where: q = Receiver angle in degrees. V = Scan velocity in degrees per microsecond. T0 = Time separation in microseconds between TO and FRO beam centers corresponding to zero degrees. t = Time separation in microseconds between TO and FRO beam centers. The timing requirements are listed in Table 6 and illustrated in Figure 7. VerDate Sep<11>2014 08:20 May 17, 2019 Jkt 247048 PO 00000 Frm 00866 Fmt 8010 Sfmt 8010 Y:\SGML\247048.XXX 247048 EC15SE91.011 856