TRANSISTOR OSCILLATOR FOR MULTIFREQl 



K\(\ IMLSING 



1327 



The effect of the various factors mentioned before on the frequency of 

 operation are shown in Fig. 12. Since several of the factors causing a shift 

 in frequency were in the negative direction only, the adjustment hmits 

 were set correspondingly higher. The over-all frequency variations could 

 be reduced by reducing adjustment tolerances. 



The starting condition is important in this type of circuit since energy 

 must be introduced into the oscillatory circuit before the dynamic char- 

 acteristics of the circuit become effective. This means that the build up 

 time is dependent upon the amount of energy introduced into the system 

 at the start. In this application energy is introduced by the current which 

 flows when the dc voltage is apphed to the collector circuit. The value of 

 this current is largely dependent upon the collector to base dc resistance 



i.oif 



EFFECT OF TEMP 

 ON COIL 

 AND COND 

 ±0.2% 



EFFECT OF 

 LOAD -0.1% 



ACCEPTABLE 

 ADJUSTMENT 

 + 0.7% -0.3% 



"^NOMINAL 



EFFECT OF 



EXCESSIVE 



FEEDBACK 



-0.25% 



ACCEPTABLE 

 LIMITS 



0.99f 



Jl 



"^(700,900,1100,1300, 1500 OR 1700'V.) 



Fig. 12 — Frequency of output with effect of various factors that may alter 

 the frequency indicated. 



which is in turn affected by the ambient temperature. This resistance is 

 between approximately 4,000 and 20,000 ohms. 



The oscillograms shown in Fig. 13 illustrate this effect. Both are for 

 the same circuit operating under normal conditions of adjustment. Qi 

 for this condition is approximately 18. Oscillogram (a) is for the applica- 

 tion of voltage in the normal fashion to the voltage divider circuit. The 

 closure occurs at the point oscillation starts. Oscillogram (b) shows the 

 build up obtained when no impulse is applied to start oscillation except 

 for minor irregularities in the dc voltage applied. Starting is prevented 

 in this case by a short circuit on 4-5 widing that was removed approxi- 

 mately 2 ms after the start of the trace. The amolitude of oscillation is so 

 low however for the first few cycles that the start is difficult to distin- 

 guish. The build up time for (a) is approximately 27 milliseconds and for 

 (b) it is approximately 37 milliseconds. The exponential build up of ampH- 

 tude is modified greatly by the rapid change in the transistor's a as 

 the voltage approaches the cutoff region. 



It should be noted also that oscillation would not have started under 



