Colpitts Crystal Oscillator Circuit

Question

In the last couple days I have been experimenting and learning about crystal oscillator circuits. I am doing this with no particular application in mind. I have been able to get a couple circuits to work as expected but there is one circuit that I got from the book " Practical Electronics for Inventors" by Paul Scherz and Simon Monk that I have not been able to get working. I have tried different transistors and I have tried varying the values of the support passives. I am wondering if anyone has had experience with this circuit and can give me a hint as to where to look for my failure to get it to work. There is also one other possibility. This book has been known to include errata from time to time so I wouldn't be completely surprised if there is something wrong with the circuit. Any insights would be appreciated.

John

shabaz · Accepted Answer

Thanks for bringing up the interesting topic, I had some fun experimenting briefly.

This was the circuit I tried, it works (well, it oscillates) although I have no idea about the quality of the output, I didn't check beyond listening for the carrier,

and the output was not loaded (so basically "it works" is a big simplification ; ) Enough output is present at 90MHz, to use a normal FM radio

to test too.

R1 at 1k also worked, C1 I changed between 39pF and 100pF and it still worked, and L1 I removed and it still worked (output level and

quality could be poor). Replacing C2 with a short worked too. I ran the circuit from a 9V PP3, not 12V.

X1 was a super-cheap typical HC49/U (i.e. large can, through-hole) crystal intended for (say) microcontrollers.

Replacing it with a 4MHz crystal also oscillated but output was noticeably less because signal strength was lower.

So, looks like BF199 should be in the basket, and 2N2222 is a bad choice in that book : (

michaelwylie · Answer

I found this information: The information is from here

Colpitts Crystal Oscillator Circuit

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