overtone xtal oscillator for PLL
would like to ask about the overtone xtals data sheet , i find that it gives the 1value of motional cap for every overtone, however i expected to see 2 different cap values for the 3rd overtone as example, why ?
is it possible to suppress the fundamental tone using electrode structure , or it should be filtered using the ct. ?
can i use a mosfet ct. instead of BJT for overtone (example, removing BJT from butler and replace it with mosfet)?
iam trying to make 150 MHZ 3rd, or 5th overtone using MOSFET , it should be implemented for a PLL
Many questions you have can be best answered if you study e.g. the ARRL Radio Amateur's Handbook. There are several useful circuits to run a xtal in overtone. Not all crystals are good in any circuit, you will have to try and experiment. I used a grounded-base RF NPN transistors with the crystal in base circuit and the overtone output in collector circuit. The emitter was grounded through a capacitor trimmer to optimize the harmonic operation. Some crystals run in overtone mode very easily, others do not like to.
so can u help me till i download that handbook , thank u :D
Simply build an oscillator at the resulting frequency; I can recommend the one above. Then replace the capacitor (1 nF) from base to ground with the crystal and try again. You will need to "tune" the trimmer from emitter to ground for the best output at crystal harmonic.
For me it always worked well, sometimes some crystals did not like "my" harmonic and I had to select one of two -three. The DC current should be adjusted also to achieve a reliable start; do not attempt to get too much power output. Typically I had 8-10 mW output, just fine to lock a PLO or a synthesizer.
should it be BJT ? (i need to implement it using mosfet sir ), that was my question
I prefer bipolar transistors but with a good RF MOSFET you should be successful, too. You can try a Pierce-type circuit, with the crystal in feedback. As I wrote, there are dozens of good circuits, choose what you prefer and try.
thank u jiripolivka