[time-nuts] bad ocxo or measurement artifact ?

[J. Forster]

Really, using a scope is not a good way to check an oscillator with such a
high output frequency. Even a Tek 7104 (1 GHz Real Time) would only show
the 3rd and 5th harmonic. It's a job for an SA, IMO.

-John

==============



> 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
>
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