Hi Joe I am just a radio amateur and I build a lot of oscillators for my need, including a GPSDO "tunable" with CW25-TIM GPS receiver chip set. Please allow me to share my usual trouble shooting when oscillator is not working properly. I see an oscillator is just only a high gain amplifier with positive feed back via "narrow band pass" filtering to sustain an oscillation in a controllable manner. I had a look at your circuit with all Vcbe of all transistors transcribed, it seems to me all transistors are within normal limit (bias # 0v7). Please look at the "narrow filter", my suggestion is to check this circuit. 1) 22pF in parallel with a serial (10uH - 30pF) is a diplexer, high impedance to ground for 10 MHz and low impedance to ground for unwanted spectrum. 2) 80 pF feed back capacitor. 3) 10 MHz Xtal
Now I can perform a differential diagnosis: All transistors are correctly biased, can eliminated fault from power supply and transistors. A quick and dirty approach is to do a loose coupling (capacitor or inductor) with the 10 uH inductor, connect to an external 10 MHz variable output source, check gain of all transistor stages to the last output Check high impedance to ground for 10 MHz, disconnect the "diplexer", check magnitude of output signal, signal is increasing, hurray we see the problem. Same signal level, put the diplexer back to the circuit, check the 80 pF cap, all else failed, the last component of the "narrow filter" is the Xtal. Good luck Pascal Nguyen vk2ihl / xv2pn _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
