or R7 in the readout unit, Figure 19) is adjusted to provide a suitable level of driving current 
for the tone detectors. This current may be measured by reading the voltage drop at the test 
points which are across a 1-ohm resistor in series with the tone relays. Since the value of 
the driving current is subject to change if the system is expanded, the correct levels will be 
posted in the console. 
2.2.3 Test Unit 
A small tone detector test unit (Figure 35) has been constructed for testing the 
control circuits tone equipment. The unit is designed to plug into the motor-generator, motor- 
alternator, and spare tone outlets on the demodulator unit. The indicating lamps are arranged 
to show when the relays are closed. 
In case of trouble with the tone circuitry, the tone relays should be checked first 
since they contain a vibrating contact which is subject to wear. In most cases it will be 
desirable to replace defective relays instead of attempting repair. 
2.3 MIXING NETWORKS 
The tone and subcarrier oscillator mixing networks in the control section of the console 
equipment and in the readout section of the model equipment are arranged so that each of the 
oscillators may be adjusted to supply the proper amount of signal to the PM transmitters. In 
addition to these, master amplitude controls for the transmitters are included. The levels for 
the individual signals are determined by setting up a modulation schedule based on the 
modulation sensitivity and the maximum allowable frequency deviation of the transmitter. 
Since the procedure for setting up this schedule is described in Reference 8, no attempt will 
be made to cover the subject in this report. It should be noted however, that only one of four 
tones in the propulsion-control system is on at a time. Each tone oscillator is set for the 
same amplitude and the modulation schedule is set up as though only one tone is being used. 
Since additional channels may be added to the system, a current modulation schedule for the 
control and readout links will be posted in the console. 
2.4 TRANSMITTERS 
The alignment and maintenance of the transmitters is fully described in the manufacturer’s 
literature.4 It should be noted that the transmitters are operated on a 200-volt supply instead 
of the 250-volt maximum. This reduces power output to about 2 watts. 
2.5 RECEIVERS 
The alignment and maintenance of the receivers is fully described in the manufacturer’s 
literature. ° 
IV-3 
