Converting power oscillator for receiving

Hello I have found this power pierce oscillator in an old magazine and I have tried it with sucess, using the 2n2166 which gave max output at 3.5W.

I have also seen this circuit http://py2ohh.w2c.com.br/trx/pititico/pititico.html which is another type of oscillator that is used as a self oscillating mixer in receive mode.

I was wondering is I could convert the first circuit somehow, so that it is used as a self oscillating mixer.

Any ideas would be appreciated.

I wouldn't bother. The 'pititico' works by starving the transistor of current so it stops oscillating (or gets very close to stopping) in order to make it a high gain amplifier with a tuned circuit. Although not very sensitive, the incoming signal will be fairly large compared to it's own signal.

The circuit in the link (which I think might shatter some crystals!) has no method of controlling the current, in fact by virtue of the diode it is self biasing. If you increased the resistor value to limit the current, it would make it less likely to start oscillating at all but still risk bursting into high power mode.

Brian.

So first, the receiving signal must be more powerful than the "oscillator", in order to receive?

Is it true that bigger package crystals, like these vintage HC-6U or even FT-243 are able to pass more current through them, thus better in power oscillators?

I was thinking of adding an emitter resistor so the gain of the transistor drops. I have no idea how much it would be allowed to drop before oscillation stops.

The two are relative to each other, what you are trying to do is either make a high-Q tuned amplifer (if not oscillating) or a direct conversion mixer if it is oscillating. In the mixer situation, you want the signal level and oscillation to be approximately equal for best results but bear in mind the signal may only be a few uV and the oscillation might be several volts, in other words, several million times stonger!
Arguably, ANY power oscillator is a bad one as they invariably produce distorted output. It's quite likely that older ones were more rugged than new ones though. As a rule, the current through a crystal should be kept as low as is practical, they are after all mechanical resonators and can be shaken to death!
The issue with that design is it would be difficult to control the point where oscillation starts. In a 'gentle' oscillator you can usually bring it to the point of oscillation then back it off agin to stop it, that design would likely do nothing up to a certain point then burst into high power mode. I thnk you would find the resistance needed to start and then stop the oscillator would be quite different, once it was going it would try to keep going. It would make it difficult to find the optimum gain point.

Brian.

Thanks a lot!