Most Helpful Member
So the writeup I am working from says to adjust the circuit such that the air/open setting on the capacitor is about 1.3 MHz.
As discussed earlier, although this oscillator circuit works, it does have its limitations.As I went to higher frequencies and amplitudes, I found that the waveform shifted from an almost sawtooth form (rounded on the rise) to what you see here. I was able to get the frequency up to 1 MHz and the amplitude up to about 500 mV, but as I did so, the bottom of the waveform seemed to get cut off (like you see in the picture, but more extreme) and the smaller extra peak before the main peak grew in prominence. And that extra peak seemed to depend as well on the external cell capacitance, leading me to worry that the frequency counter might start picking them up as separate pulses, screwing up the measurement.
Scratching my head, I remembered a circuit for a 1MHz oscillator which I knocked up for someone a few years ago.
It runs at 1MHz and is easily adjusted by varying the turns on a single layer coil.
The output from the emitter of the transistor is a close approximation to a sine wave with an amplitude of nearly 2.5v p-p.
To re-iterate what I said yesterday:
JimBIf I were starting from scratch, I would select an oscillator circuit which used a simple inductor (ie just one winding).
Then using a reel of wire and suitable former, it would be easy (five minute job) to make whatever inductor was required.
PS, I think that I have "oscilloscope envy".