Stanley Reynolds wrote:
Looking at the output of Greenray Industries Y-313-16A 160 MHz OCXO I
discovered a new feature of my Hp 54501 scope. It split the signal into 4
traces each with a different amplitude and they are phase shifted from each
other. P to P levels are 2.8V, 116mv, 53mv, and 9mv. Not much difference
running the oxco on a battery or substituting the scope probe with coax cable
rg58 6' with a tee and 50 ohm termination.
Could this be a aliasing effect of the AD sampling the as the scope is a
digital 100Mhz scope ?
No I don't know what I'm doing :-) But I would like to know.
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
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