The subcarrier channel signals are separated from the composite receiver output by 
the frequency-selective input circuitry of the discriminators. Following stages of the discrim- 
inators clip and demodulate the subcarrier signal and produce an output current or voltage pro- 
portional to the signal applied to the subcarrier oscillator in the transmitting end of the radio 
link. The discriminator is insensitive to variations in amplitude of the input signal, above 
threshold, and responds only to frequency variations. Two controls, for balance and output 
level, are provided in each discriminator in addition to a meter which indicates relative 
amplitude of the output signal. 
The low-frequency tone signals are separated from the composite receiver output signal 
by a low-pass filter. The tone signals are then amplified and applied to a group of resonant- 
reed relays. These relays are highly frequency-selective and are tuned to frequencies matching 
the resonant-reed oscillator-control units in the transmitting end of the radio link. The con- 
tacts on the resonant-reed relays close for only 5 percent of each cycle of their resonant fre- 
quency and have limited current-carrying capabilities. These short contact closures are used 
to charge a capacitor in the grid circuit of a vacuum tube amplifier. The plate circuit of the 
amplifier contains a multi-contact relay which is capable of handling the currents required 
by other sections of the control or readout instrumentation. 
3. CONTROL EQUIPMENT 
3.1 RUDDER CHANNEL 
The rudder control system is designed to operate one or two rudders from a common 
servo system. Three groups of rudder controls are included to handle various types of 
maneuvering tests. The PRESET or STEP methods of control should be used when it is 
desired that the rudder run into a new position at a constant velocity. The WHEEL control 
will be most useful for random maneuvers and for adjustment of average course when an ex- 
ternal programming signal is used. The servo system is designed to be used with the radio- 
control link or in a cable-controlled system. It may be used as a simple proportional servo, 
with a no-load run-in rate of about 56 degrees per second which is desirable for external pro- 
gramming, or as a velocity-stabilized system with adjustable run-in rate. The servo unit 
contains adjustable limit cams which reduce servo torque at any desired shaft positions. 
Mechanical linkage is provided for coupling a second rudder shaft to the servo unit. An adapter 
plate and two bearing assemblies are included for using existing rudder-force dynamometers 
on one or two shafts. 
All console rudder controls are mounted on the left panel of the console, Figure 5. 
Type of control is selected by the switch on the left side of the panel. The first type of con- 
trol is PRESET. In this mode of operation the three controls at the top of the panel are used. 
The multiturn potentiometers are calibrated directly in degrees and may be set for any desired 
Port and Starboard rudder angles. The selector switch at the top center of the panel may 
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