I'm pleased to report some good news about the Si5351A Breakout Board reference oscillator situation. While the original Abracon TCXO is still basically unavailable as of the date of this post, I have found a suitable replacement TCXO for now. I spent a few days in the lab running a batch of test boards through the normal test and calibration routine (which they passed with flying colors), but also doing extended testing on frequency stability, temperature sensitivity, and very narrowband TCXO tuning compensation behavior. The new TCXO looks at least as good as the Abracon osc, and could possibly be even a bit better (although that's based on an estimation, since I didn't directly put the two different oscillators through the same tests at the same time). They are certainly suitable for the Si5351A Breakout Board according to my standards, so I will be using these going forward.

I've secured a decent amount of these, which should keep me supplied for at least a few months. Once the Abracon oscillators are available again, I may continue to use them if supplies of this new oscillator become scarce, but I don't expect that users will notice any significant difference between the two.

Also, I wanted to note a small change in the Si5351A Breakout Board calibration report due to some confusion. In previous reports, the calibration factor was written in the sign needed to add or subtract from the nominal 25 MHz ref osc frequency (in other words, if the ref osc was 1000 ppb high, the report would print the correction as "-1000 ppb"). However, in the Etherkit Si5351 Arduino library, the factor you need to use to set the correction has the opposite sign, so in the previous example, you'd need to put in a positive correction, not negative. From this date forward, our calibration reports will use the latter standard, so that you put the number printed on the calibration report as is into the Arduino library correction method.