2.1 SUBCARRIER OSCILLATORS 
2.1.1 Potentiometer Controlled 
Each potentiometer controlled subcarrier oscillator has individual adjustments for 
setting the high and low band limits and the output level. A test point is provided for check- 
ing oscillator frequency. The control circuit subcarrier oscillators are shown in Figure 19 and 
the readout circuit oscillators in Figure 52. A list of subcarrier frequencies versus control or 
readout potentiometer settings is mounted in the console. When setting the subcarrier 
oscillators a digital frequency meter should be used for checking frequency; this frequency 
meter may be connected directly to the test point of the oscillator. After allowing at least 
30 minutes for warmup, adjust the HIGH and LOW controls to obtain the frequencies listed on 
the chart. Repeat the adjustments if necessary as there is some interaction between controls. 
The procedure for setting the output controls is described in Section IV, 2.3. 
2.1.2 Reactance Controlled 
Reactance controlled subcarrier oscillators are used only in the rpm pickup circuitry. 
The frequency of the oscillators is adjusted by positioning the E-core pickup coil relative to 
the segmented wheel and by soldering silvered mica capacitors across the tank circuit within 
the oscillator. The poles of the E-core should always be parallel to the axis of the propeller 
shaft, and the distance between the core and the wheel varied by adjustment of the two 
lock-nuts. A preliminary check on the frequency deviation of the oscillators may be made by 
slowly rotating the pickup wheel and observing the deflection of the indicator on the discrim- 
inator. For a complete check, the output of an accurately calibrated discriminator should be 
connected to an oscilloscope. The pickup wheel should be rotated at speeds of from zero to 
3000 rpm and the pickup and tank circuit capacity adjusted so that maximum frequency de- 
viation is obtained without exceeding the band limits. It should be noted that the capacity of 
the cable from the pickup to the oscillator forms part of the tank circuit and any changes in 
cable length must be compensated by retuning the circuit. The output control on the 
oscillator should be adjusted as described in Section IV, 2.3. 
2.2 TONE CIRCUITRY 
2.2.1 Tone Oscillators 
There are no adjustments to the tone oscillators except the output amplitude 
controls. The adjustment of these controls is described in Section IV, 2.3. 
2.2.2 Tone Detectors 
The tone detector circuitry consists of a common audio amplifier which drives a 
group of resonant reed relays. A gain control in the amplifier (R1 in the tone detector unit, 
IV-2 
