[time-nuts] bad ocxo or measurement artifact ?

Stanley Reynolds stanley_reynolds at yahoo.com
Sat Jan 16 21:50:56 UTC 2010


The HP 54401 has 100 MHz bandwidth, but only 10 Msa/s sampling rate at the most. Channel 1&2 mux into a common T/H and A/D and similarly for the channel 3&4. I could not find the fact in the manual, but I suspect that enabling channel 2 and 4 lowers the sampling rate. It's quite common.

Regardless, sampling a 160 MHz signal with 5 or 10 MHz sampling rate causes alot of aliasing phenomenes. The scope is undersampling for all signals above 5 MHz. Undersampling scopes can be confusing until you master it. It's a fine compromise, but the burst-sampling rate is getting very high now.

Cheers,
Magnus

Yes when I disable channels 2-4 the display looks better without the cross-talk the waveform is still a little asymmetric on the negative side, maybe the calibration issue John mentioned. The way the display updates with parts of the wave form changing over several seconds I understand now, thinking about the under sampling, and it is more noticeable at this high frequency.

Guess the OCXO waveform is OK now off to check stability .....

Stanley



More information about the time-nuts mailing list