So the first attempt at a switching power supply was a bust. But while the TCXO that I'm using does meet the performance goals, I'd really like to at least try an OCXO to see if the performance is worth the extra $20. The problem with an OCXO is that it requires two orders of magnitude more power, and it's just too much to ask for an LDO to come up with it.

The SC189Z fixed 3.3v buck converter looks like a miracle solution. In particular, it runs at ~2 MHz and the datasheet has ripple graphs (under load, no less) that are incredible to behold. It's also reasonably cheap and requires (in addition to parts that are already on the board) only a single 0805 inductor. It can come up with up to 1.5A @ 3.3v. It does, however, require input voltage no higher than 5v, so a 5W 5V power supply would be called for. In addition, assuming that it lives up to its stability promise, it would be conceivable to have one board support either the DOT050V TCXO or the DOC020V OCXO, with the latter being a premium option.

I've ordered some prototype boards to try this out. The real test is going to see the 4 cornered hat with the Rubidium standard, the current version of the board, the next one with the TCXO and the next one with the OCXO.