Radar System Engineering

582 PRIME POWER SUPPLIES FOR RADAR [SEC. 14.9
rectifier cathodes may use up a )arge part of the 50 to 60 watts of available
power.
Two or more vibrator power supplies can be designed for operation in
series or in parallel on the d-c output side, so that larger currents or
voltages can be obtained from small vibrators. Large vibrators, capable
of supplying 200 watts or more from 12- to 14-volt or 24- to 28-volt d-c
supplies, are available, but it is usually more. convenient to use conventional
inverters with transformer-rectifier power supplies for outputs
greater than 250 watts.
Vibrator power supplies usually give efficiencies of 50 to 70 per cent,
based on d-c output vs. d-c input.
Precautions must usually be taken to reduce radio interference from
vibrator power supplies. Small r-f chokes in the power input leads, mica
r-f bypass condensers on input and output, and careful shielding and
grounding usually provide adequate radio interference suppression for
aircraft use. Where extremely low noise level is required it may be
necessary to shield the vibrator, transformer, and each d-c ripple filter
separately, and use r-f chokes in each transformer connection. However,
it is usually less troublesome to suppress radio noise in a vibrator
supply than in a small dynamotor.
Vibrators can be obtained in hermetically sealed containers, making it
possible to design power supplies for operation under extreme conditions
of altitude and humidity.
Production-type small vibrators are available with reed frequencies
from about 100 to 115 cps. These vibrators have a useful life of at least
500 hours when used with well-designed power supplies.
Vibrators have recently been developed with reed frequencies of about
180 cps. Smaller transformers can be used at this higher frequency, so
than an over-all weight reduction of 20 to 25 per cent may be achieved.
The life of such vibrators may be somewhat less than that of low-frequency
vibrators. A more complete treatment of vibrator power SUPplies
is given in Vol. 17, Chap. 12 of the series.
14.9. Summary of Recommendations for Aircraft Radar Power.
1. Consider the radar-radio power-supply problem of a specific aircraft
as a whole. What dynamotor can be eliminated? What
inverters can be combined? Is all equipment uniformly designed
to operate from one standard a-c source? Often enough weight
can be saved to justify such refinements as an electronic voltage
regulator.
2. Use a direct-driven generator whenever possible, either at constant
frequency (if airplane is so equipped) or at variable frequency. If