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Determining the frequency of a colpitts oscillator

时间:04-08 整理:3721RD 点击:
I have designed the attached colpitts oscillator however i'm not sure at which point on the circuit should I put the probes to test the frequency( i'm using a frequency counter and also a multimeter which can measure frequency)(by the way i do not yet know whether my circuit oscillates)

Could someone help me from the schematic attached how will i go by measuring this frequency.

many thanks in advance.I will highly appreciate your input as I have been struggling with this for some time!

I guess it doesn't, because of a rather unsuitable dimensioning. The 1 nF capacitor doesn't provide enough feedback, I fear. Also the collector to emitter resistor ratio seems too high.

You should check the signal in the point between the 1nF capacitor and the inductor.

Also, you should use an oscilloscope instead of a multimeter and frequencimeter.
Multimeter's input impedance can be low (100kΩ for analog multimeters) which will affect the circuit and may prevent it from oscillating. Maybe that's not your case.

Oscillation frequency should be around:

f=1/[2Π√[L*(C1*C2)/(C1+C2)]] if we ignore the resistors and transistor impedance.

Unless the transistor has a too low beta, it is in saturation.
You should start choosing the polarization point of the transistor.
The collector resistor can be replaced by a suitable RF choke (in that case the transistor will not be saturated).
Regards
Z

Thanks for all the reply.Sorry for the confusion, the capacitors are microfaradays, sorry the u looks like n.

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