Pixie tests with VXO and Ceramic Resonators.

Quick test today using ceramic resonators.
40m model:
Even with a 5 - 60pF variable capacitor the frequency could be pulled down to under 7.000MHz, with a ceramic resonator for 7160kHz. The stability, however, was not sufficient with the Pixie. The tuning was fiddly, and the TX signal had a significant chirp, and the receive frequency was drifting too much for my taste. Well, it was clearly audible ...
Further, the RX offset of the oscillator, when using a crystal in series with the variable capacitor, was insufficient at the lowest frequency, even when it was set to maximum, i.e. the RX local oscillator (BFO) was too close to zero beat.
The 80m version did not fare much better. Yes, it was a bit better, but still had chirp on the TX and some drifting on the RX the RX could not be pulled down to the band edge, either, but did have a sufficient range to have been useful.

More experiments with an inductor added to the VXO (crystal) should be an interesting experiment. It might provide for a better stability, and somewhat better offset. This needs to be tested.

It may be possible to use one Pixie as RX and another as TX, providing a "spot" function, but I doubt the stability will be sufficient with the ceramic resonators.

Because VK3YE has tested oscillators and even regenerative receivers with ceramic resonators, and achieved sufficient stability for CW operation, I would consider the Pixie as too simple for good results as a frequency agile CW transceiver. It would be quite suitable for simple fixed frequency operation, e.g. as a monitor receiver for FT8. Crystals for such a receiver (20m and 40m) should arrive in about a week, if not delayed by the corona virus situation. A test of the Pixie as a simple QRSS RX should be another simple experiment.