Service manual

STP 11-25R13-SM-TG
U - 12
(a) Compressor/dehydrator units to supply regulated dry air can be fully automatic (the desiccant is
dried out periodically by the unit) or semiautomatic (where the desiccant must be replaced or dried out by
an operator).
(b) To avoid rapid cycling of the compressor, the volume of air in the system should not be less
than 1.5 cubic feet; this can be achieved in small systems by fitting a regulating tank. The typical loss per
hundred feet of several types of feeder is listed in Table U-1.
Table U-1. Typical Loss per Hundred Feet of Cable
d. Passive Repeaters. On some hops a passive repeater is used to clear an obstacle rather than
an active repeater. The passive repeater may be either a billboard type or two parabolas back to back.
The flat billboard type has efficiency near 55 percent.
(1) Because the "gain" of a passive repeater of a given size is proportional to the square of the
frequency, their use is mostly limited to frequencies of 6 GHz and above.
At 950 MHz/Loss per 100 feet
Foam dielectric (aluminum) coax:
1/2-inch diameter = 3.7 dB
7/8-inch diameter = 2 dB
1 5/8-inch diameter = l.4 dB
Air dielectric coax:
7/8-inch diameter = 1.6 dB
1 5/8-inch diameter = 0.8 dB
At 7 GHz/Loss per 100 feet:
Elliptical waveguide EW-63 = 1.4 dB
Rigid rectangular waveguide WR 137 = 1.8 dB
At 13 GHz/Loss per 100 feet:
Elliptical waveguide EW-63 = 3.6 dB
Rigid rectangular waveguide WR 75 = 4.2 dB
At 18 GHz/Loss per 100 feet:
Elliptical waveguide type EW 180 = 5.9 dB
Rectangular waveguide WR 42 = 14 dB
At 2 GHz/Loss per 100 feet
Foam dielectric (copper) coax:
1/2-inch diameter = 3.5 dB
7/8-inch diameter = 1.9 dB
1 5/8-inch diameter = l.4 dB
Air dielectric coax:
7/8-inch diameter = 1.9 dB
1 5/8-inch inch diameter = 1 dB