For a rubidium frequency standard, there are usually two separate things to check:
- Is the rubidium physics package actually locked?
- Is the 10 MHz output present and stable?
On most rubidium modules, the best indication is a dedicated LOCK / UNLOCK / STATUS output. After power-up, the unit warms up, searches for the rubidium resonance, and then changes the state of that pin when lock is achieved. This commonly takes a few minutes, although the exact behaviour depends on the module.
You can also check the 10 MHz output with an oscilloscope or frequency counter. You should see a clean, continuous 10 MHz signal almost immediately on many units, but the presence of 10 MHz alone does not prove rubidium lock—during warm-up the oscillator can still generate 10 MHz while the atomic servo has not yet locked.
For the refurbished rubidium board you bought, the most useful test would therefore be:
Power supply → rubidium board → monitor LOCK/STATUS pin + measure 10 MHz output.
Once locked, you could feed the 10 MHz into a good frequency counter. An ordinary counter will verify that it’s producing approximately 10,000,000 Hz, but demonstrating the accuracy of the rubidium standard requires a better reference—typically GPSDO, another known atomic standard, or a suitable comparison technique.
If you want, I can go back to the photos of the actual rubidium unit you bought and identify exactly where/how to check its lock indication and what voltage or signal you should expect.