Try looking for abnormalities on a LORAN-A pulse, for example... a few 10s
of uS of 2 MHz every few 10s of mS, or a disk drive data stream
abnormality.
-John
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So I'm finally getting to unpack all my gear and set up a lab again. As
part of
setting up my bench I am doing basic functionality checks on the
instruments I
intend to use. One is a "straightforward" HP 5335A counter. Hooked it up
to a
HP signal generator putting out a nice 5 volt sine wave at 1000 Hz. What
does
the counter tell me? Around 1800 Hz and unsteady. Analog scope tells me
it
looks great, nice and clean... Try it again on the counter and 1000 Hz on
the
nose and rock solid. I've found in the past that it is very easy to get
the
second harmonic reading on a counter as well. And DVMs, forget about it,
some
read AC riding on DC very strangely, or if you have a non-true-RMS
meter...
There are many cases where you need to understand what you are looking at
and
what you are expecting. You need this to sanity-check the instrument as
well as
to understand what you need to do to verify your reading. Yes, analog
scopes
can show you a very true picture of what's happening but you can easily
miss
some massive fast/short transients too.
To get the most from this gear you need to understand each instrument and
what
it's limitations are. You need to know your tools.
Now what's up with that 5335A and the strange result I am now unable to
duplicate? ;-)
Now back to work...
On 12/31/2012 10:33 AM, J. Forster wrote:
IMO, you simply cannot trust what you see on the screen of a sampling
scope.
-John
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