Find a list of ATSC pilot frequencies.? They are usually network disciplined.? Try several - I see 2hz variation between them in my area.? This way you can judge the warmup drift of your instrument.? For Ham use, TCXO is plenty good if you calibrate it at lab temp, and you wont have to worry about warmup drift with the OCXO.? If I am really picky, I will let the OCXO warm up for at least 1 hour, but maximum stability is reached by 2 hours.? At room temp, the TCXO will be ready for use while the OCXO will have to wait at least 20 mins to do better.
My other answer was to get one of those surplus e-bay 105243 OCXO, build up a clean power supply for it and leave it running all the time. This is as accurate as warming up the OCXO in my 8920a for 2 hours.
I wonder if there are any issues with keeping the internal OCXO warm with 9v or so from an external dc supply with diode isolation?
