I would like to add some perspective to this discussion. The 10811 oscillator simply uses a plain vanilla Pierce circuit configured so that one terminal of the crystal is at ground. The base emitter capacitor is replaced by a mode suppression network to force operation to the correct overtone and mode (C as opposed to B). It uses a common (at the time) transistor, the 2N5179. The AGC varies the DC collector current in the transistor. A zener diode of a type which is known to have low noise is used to bias the varactor. There is no magic here.
The results are that below 100 Hz, the noise is strictly determined by the intrinsic crystal noise (yes, crystals have their own noise). Intrinsic crystal noise can be measured with an HP3048 type phase noise system, if you know what you are doing. At 1 kHz and above, the noise is strictly determined by the buffer amplifier following the oscillator circuit. Read Rob Burgoon's patent to understand why his patented buffer is the best that can be built (ie limited by physics). The actual buffer used in the 10811 has some compromises in it that increase the phase noise floor. You can easily get back to optimum performance by using a string of common base amplifiers. It is therefore puzzling to me that there is a search for the holy grail low noise oscillator circuit. What is it that you do not like about the 10811 circuit? Rick Karlquist N6RK _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
