[G0HZU_JMR]

I couldn't resist trying the MMIC oscillator in the shielded enclosure when set for a loop gain margin of just over 1dB and a lowish output power. This required 5dB attenuation in the feedback and a reduction in bias current to 27mA. This keeps it close to that sweetspot region where the onset of oscillation (rising from the regenerative noise peak) only gives a 20Hz shift in frequency

There is about -5dBm at the analyser but this is via a 10dB attenuator. So the power that is split to the resonator is (+5dBm - 5dB) in the feedback attenuator = 0dBm.

Because this is a 5V MMIC and I'm biasing it from about 12V via a dropper resistor and an active supply filter circuit there is about 330mW Pdiss on the PCB. This means that this oscillator drifts a fair bit from cold. However, I left it for 45minutes in the enclosure to stabilise and then measured the drift at just 60Hz in an hour and a half! This is at twice the frequency of the 5.2MHz Franklin oscillator. The close in noise plot on a 100Hz span is given below and this is notably cleaner than the 100Hz plot of the (already impressive) Franklin circuit given earlier post #32 and I've repeated this plot below on the right.

At this lower power level and with minimal gain margin in the feedback the trainer oscillator now has a sharper and cleaner peak and it shows less phase noise close to carrier. I think it just edges out the Franklin oscillator on drift as well. However, the MMIC oscillator would be a worse choice as a VFO because of the warmup drift. Also, I suspect it will drift a lot if I were to subject it to a step change in temperature.

It would be interesting to try building this circuit with the MMIC on an ally heatsink and with a remote airwound resonator a few inches away. This would hopefully improve the warmup drift.