Radar System Engineering

SEC. l’k~~] SHIP RADAR SYSTEMS 587
lators have a tendency to be unstable, exhibiting rapid hunting of about
20 to 40 cps. This may not be troublesome on lighting or motor loads,
but it is one of the major causes of spoking of PPI displays and instability
of other forms of radar presentation.
One method of using regulators has been followed with some degree
of success. That is to provide a rheostat in series with the regulating
resistance of the regulator in the field circuit. Assuming that 115-volt
output is desired, the regulator can be adjusted to regulate at 118 to 120
volts and enough resistance cut in, by means of the rheostat, so that
the voltage is 115 volts at full radar load with everything at normal
operating temperature. Under normal operating conditions, then, the
regulator is all out and not functioning. If the voltage should rise, as
during warmup period or when the radar is on stand-by, the regulator
will cut in when the voltage comes up to 118 to 120 volts and prevent
further rise in voltage. If there is a load greater than normal causing the
output voltage to drop, the manual rheostat will have to be adjusted.
However, with the motor-generator set acting as an electromechanical
flywheel to take up transient fluctuations in the ship’s power supply,
operation is reasonably steady and satisfactory.