L5 System: 39A Precision Oscillator

The 39A oscillator was developed to meet the precise frequencycontrol requirements of the L5 jumbogroup frequency supply. The need for frequency control as exemplified by the 39A oscillator is explained in the paper on the jumbogroup frequency supply in this issue. This 5.12-MHz precision oscillator is characterized by long-term stability of 1 X 10~10 per day, and by short-term stability of 1 X 10~8 for a 1-millisecond sampling time or 2 X 10 _u for a 10-second sampling time. External frequency control is accomplished utilizing a compatible digital word applied to the oscillator's 14-bit, TTL, precision, digital-toanalog converter. Setting range of the converter is > ±4 X 10 -7 , which gives a least-significant-bit resolution of X 10 -11 ; the converter section incorporates a linearizing network to reduce the frequency-set deviation from a straight-line function to ± 5 X 10-11 over a ±4 X 10~8 tuning range, and to a maximum variation of tuning sensitivity of ± 3 0 percent over the entire range of ±4 X 10 -7 , with less than ± 1 X 10-10 departure from a smooth curve. 2097