Dave M wrote:
... Here are some
attributions that elaborate on the effects of a probe on the overall
bandwidth of a scope/probe combination.
http://books.google.com/books?id=xHA...0probe&f=false

http://www.adler-instrumentos.es/ima...%C3%B1al.pd f
pg 3

http://www.freelists.org/post/si-lis...nt-equipment,9

http://www.analog.com/library/analog...cd/vol41n1.pdf pg 13

As you can see from the documents, the scope and probe bandwidths do
interact as the RMS sum of the two. The vertical bandwidth or
risetime of scopes is specified at the scope's input connector. If
the bandwidth specification includes the probe, it will be specified
as such. In those cases, the scope's bandwidth will be specified
separately, and will be higher than the scope/probe combination.
Vertical bandwidth on many high quality scopes will be described in
their manuals or spec sheets when using a variety of probes, and
will reflect the equivalent bandwidth accordingly.


I'm interested in seeing info on the Tektronix way that proves that I am
mistaken. I provided several sources that defend my statements. Did you
read the sources that I provided links for? All quite credible sources.
Did you do the math, or is your conclusion just an opinion? How would you
calculate the combined risetime/bandwidth of a scope/probe combination?

Please don't interpret my questions as being confrontational, I'm genuinely
interested in learning if the technique that I used for years in calibration
labs was, in fact, correct or totally wrong. The technique that we used was
this:
Using a high bandwidth scope, measure its risetime without the probe being
connected (scope connected directly to a fast-rise pulse generator).
Connect the probe being calibrated to the scope input, and connect the probe
tip directly to the pulse generator output.
Measure the resulting pulse risetime.
Using the formula that I gave previously (rearranged to find the probe's
risetime), calculate the probe's risetime and bandwidth.
This method of measuring the performance of a probe worked quite well for
the lab and our customers for the years that I was a cal technician
(commercial and military).

I started looking for a reference that I could trust - and I found it in
a Tektronix note - a note that totally supports your position.

Ooops! I was wrong - with a misplaced sense of what one can measure with
Tektronix scopes. Sorry.... I appreciate your level tone though!

http://www.tek.com/Measurement/App_N...55_18024_0.pdf


Brian Whatcott Altus OK