BendixKing IN-862A System RDR-2100 - Manual (Page 68)

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Effective Date: 9/98 RDR 2100 Pilot's Guide: Rev 1
Combustible Materials. To prevent possible fuel ignition, an installed airborne weather radar should not
be operated while an aircraft is being refueled or defueled.
M.C. Beard
Director of Airworthiness
AC 20-68B 8/8/80
8/8/80 AC-2068B
Appendix 1
APPENDIX 1. SAFE DISTANCE DETERMINATION
The following information can be used in establishing a minimum safe distance from the antenna for per-
sonnel near an operating airborne weather radar.
NEAR FIELD/FAR FIELD INTERSECTION. The distance to the near field/far field intersection can be
computed by:
Ri=G λ (1)
8 π
where Ri=Intersection distance from the antenna (in meters)
λ=Wave length (in meters)
G=Antenna gain
DISTANCE TO 10 mw/cm2 SAFE LIMIT. For a far field power density of 10 mw/cm2, the distance (in
meters) from the antenna may be calculated by:
Rs √GP/400 π (2)
where Rs=The minimum safe distance in meters.
P=Transmitted average power in watts.
G=Antenna gain
PROCEDURES. The above formulas or the graphs of figures 1 and 2 may be used to determine the
minimum safe distance. In either case, the following procedures apply:
a. Determine the distance (Ri) to the near field/far field intersection (paragraph 1).
b. Determine the distance (Rs) to 10 mw/cm2 power density (paragraph 2).
c. If the distance (Rs) determined in b above is less than (Ri) found in a above, use distance (Ri) as the
minimum safe distance.
d. If the distance (Rs) determined in b above is greater than (Ri) found in a above, use distance (Rs) as
the minimum safe distance.
EXAMPLE.
Data. The following is typical data for the airborne weather radar.
Antenna Diameter :22 inches=56 cmTransmitter
Frequency :9375 +30 Mhz
Wave Length :3.2 cm
Pulse Length :1.5 microseconds (search)
Pulse Repetition :400 Hz
Peak Power :40 kilowatts
Average Power :24 watts (search)
Antenna Gain :1000 (30 db)
Calculations:
(1) Distance (Ri) to the near field/far field intersection. (2) Distance (Rs) to 10 mw/cm2 safe limit.
The distance (Rs) is greater than (Ri), therefore, the minimum safe distance is 14.3 feet.
Ri=G λ
8 π
Ri=1000 x 0.032
8 π
=1.27 meters = 4.2 feet
Rs = √GP/400 π
=√1000 x 24/400 π
= 4.37 meters=14.3 feet
Appendix
RDR 2100 PG 3/12/07 3:45 PM Page 64