Mhz Oscilloscope Component
colpitts oscillator question?
I have built the following colpitts oscillator :
http://en.wikipedia.org/wiki/File:NPN_Colpitts_oscillator_collector_coil.png
I used 100uH L and 22pF caps and got a signal with about 2 MHz freq with 2V amplitude ,Vcc = 9v. And I used a 0.47uF cap at the output to block the DC component. I then applied the output to a 1N4007 diode to obtain a half-wave rectified signal , but when i connected the oscilloscope terminals
to the output i got no signal at all. just 0 output signal. why the diode was not biased with 2V amplitude ?
notes:
* I took the output of the oscillator from the transistor emitter to observe an AC signal , when i measured the output at the collector it gave just a DC signal.
* I tried using several resistor values as the loads between the diode output and the gnd such as 1K , 10k , 32K values and it still did not work.
In addition to what billrussell42 suggested, it seems to me you chose rather small capacitors and a large inductor for your oscillator. Because of this the output impedance of your oscillator is rather high. I suspect your oscilloscope input impedance is affecting the circuit pretty strongly, especially when you connect it to the collector of the transistor. Most scope probes have an impedance of 1 or 10 M ohms of resistance in parallel with 10 to 50 pFof capacitance. The probe capacitance is probably about as large as the 22 pF capacitors you chose, so I think it is affecting the oscillator circuit and maybe is even stopping the oscillations.
Could you choose a smaller inductor, say about 4.7 uH and use about 470 pF capacitors? This would lower the impedance by a factor of about 20 so the scope probe would not load the oscillator so much. Best of luck with your experiments. Have fun!
A look at what is currently available on eBay
 Working Hung Chang OS-620 Oscilloscope Dual Channel 20mhz With Component Tester US $61.67 
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