856 

14 CFR Ch. I (1–1–19 Edition) 

§ 171.311 

fall times shall be less then 10 micro-
seconds. It shall be permissible to se-
quentially transmit two pulses in each 
out-of-coverage indication time slot. 
Where pulse pairs are used, the dura-
tion of each pulse shall be at least 50 
microseconds, and the rise and fall 
times shall be less then 10 microsec-
onds. The transmission of out-of-cov-
erage indication pulses radiated from 
antennas with overlapping coverage 
patterns shall be separated by at least 
10 microseconds. 

N

OTE

: If desired, two pulses may be sequen-

tially transmitted in each OCI time slot. 
Where pulse pairs are used, the duration of 
each pulse must be 45 (

±

5) microseconds and 

the rise and fall times must be less than 10 
microseconds. 

(D) 

System test. 

Time slots are pro-

vided in Tables 4a and 4b to allow radi-
ation of TO and FRO test pulses. How-
ever, radiation of these pulses is not re-
quired since the characteristics of 
these pulses have not yet been stand-
ardized. 

(iii) 

Angle encoding. 

The encoding 

must be as follows: 

(A) 

General. 

Azimuth and elevation 

angles are encoded by scanning a nar-
row 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 be-
tween the beam centers of the TO and 
FRO scanning beam pulses. The TO and 
FRO transmissions must be symmetri-
cally 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 

±

10 microseconds. Angu-

lar coding must be linear with angle 
and properly decoded using the for-
mula: 

θ

=

V

2

T

t

0

−

(

)

where: 

q 

= Receiver angle in degrees. 

V = Scan velocity in degrees per micro-

second. 

T

0

= Time separation in microseconds be-

tween TO and FRO beam centers cor-
responding 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. 

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