> Again, this is analogous to the 5071A having 1 MHz > spurs of about -90 dBc, yet the ADEV is not much > different than an open loop 10811. How high would > the 1 MHz spurs have to be to affect ADEV?
With ADEV, you have to consider the measurement bandwidth before you can ask questions like this, much less answer them. :) 1 MHz spurs are far outside the restricted measurement bandwidth that would be desirable when measuring a high-performance source like a 5071A. I suppose there might be some influence if you use a DC-to-daylight sampling process such as a counter, but the instrument noise floor will probably obscure any interferers in the -90 dBc range. With a TimePod or similar device, a general rule of thumb is that a spur a few Hz away from a 10 MHz carrier at -120 dBc will cause ripple in the 1E-11 to 1E-12 range. This coincides with typical levels of coupling between nearby RG-58 cables -- see page 38 of http://www.miles.io/TimePod_5330A_user_manual.pdf for instance. That particular situation wouldn't have shown up on a traditional counter-based measurement, but others might. For instance, in your 1 MHz example, I doubt you'd see any effect at exactly 1 MHz, but if your spurs are at 1.000001 MHz and your counter is capable of 1-ns single-shot resolution, I can imagine that there will be some corruption. The exact numbers will depend on so many factors that it's almost easier to set up a test and observe the effects firsthand. -- john, KE5FX Miles Design LLC _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.