oscillator doesn't oscillate as I expect
Hello:
I am trying to test a simple oscillator to see if I can get it to work. It is based on a LC tank and uses one transistor. It uses a 10pf capacitor to turn on or off the transistor.
I was expecting it to oscillate at the 1/(2*pi*sqrt(L * C), that is about 160K HZ. However, I saw from the oscilloscope it is oscillating at about 93 MHz. Actually its oscillating frequency is not that stable. I think it might be because my scope probe loads the LC tank. The scope probe has about 90 pf.
My major question is why it doesn't work at 160K, but instead working on a much higher frequency?
Also, I found this circuit is sensitive to the base transistor, which is right now 100K. If I use a small value like 1K, the oscillation will disappear. The emitter resistor is 330, if I make it 100, the oscillation amplitude would be much smaller. So overall my feeling is that I cannot drive the transistor too hard, which may overwhelm the LC tank or heavily curb it.
Any help/discussion/point is very welcome I come here to learn!
have a nice day!
Hello:
I am trying to test a simple oscillator to see if I can get it to work. It is based on a LC tank and uses one transistor. It uses a 10pf capacitor to turn on or off the transistor.
I was expecting it to oscillate at the 1/(2*pi*sqrt(L * C), that is about 160K HZ. However, I saw from the oscilloscope it is oscillating at about 93 MHz. Actually its oscillating frequency is not that stable. I think it might be because my scope probe loads the LC tank. The scope probe has about 90 pf.
My major question is why it doesn't work at 160K, but instead working on a much higher frequency?
Also, I found this circuit is sensitive to the base transistor, which is right now 100K. If I use a small value like 1K, the oscillation will disappear. The emitter resistor is 330, if I make it 100, the oscillation amplitude would be much smaller. So overall my feeling is that I cannot drive the transistor too hard, which may overwhelm the LC tank or heavily curb it.
Any help/discussion/point is very welcome I come here to learn!
have a nice day!
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