capacitance load of oscilloscope probes

[Blue]

I am looking for oscilloscope probes. There are a number of choices on
ebay. I am looking for passive 1x/10x probes for a 60 MHz scope with
input capacitance of 30 pF.

One of the choices is a probe with capacitance that can be changed from
15-40 pF. Its capacitance load is 90pF/20pF (I assume for the two
attenuations). Would this be okay with the scope? Any other pointers
what to keep in mind wrt to the capacity of the probes?

Thanks.

 

[Blue]

That sounds like that should work fine.

Jon

Thanks. I was reading a bit more about probes and realized that the
variable capacitor on the probe is used to cancel the scope's input
capacitance. Hence the former should have the latter within its range.
However, that leaves us with the probe's own capacitance. In this case,
it is 90pF/20pF (for 1:1/1:10 attenuation). Are these values typical for
probes for 60 MHz scopes?

 

[Blue]

Yes, pretty typical. At 1:1 attenuation, the probe is basically just a
length of coax cable, and the capacitance of those is always pretty
high, tens of pF per foot for even the best. 20 pF for a standard X10
probe is about normal, some really high-end Tektronix probes with 400
MHz bandwidth that cost $400 each about 20 years ago, are 14 pF.

If you need lower capacitance, you have to go to amplified probes, and
those cost several thousand $.

Jon

Okay, thanks for the explanations.

One more point I just was wondering about. Is it typical that probes for
different bandwidths have same capacitance? e.g. should a 60 MHz probe
have the same capacitance as a 200 MHz probe? I am suspecting that
higher frequency probes are going to have lower capacitance else higher
freqs are going to be attenuated more. But I could be wrong, because
based on your explanation, at 1:1 all probes are going to have the same
capacity.

 

[StepNfetchit]

I am looking for oscilloscope probes. There are a number of choices on
ebay. I am looking for passive 1x/10x probes for a 60 MHz scope with
input capacitance of 30 pF.

One of the choices is a probe with capacitance that can be changed from
15-40 pF. Its capacitance load is 90pF/20pF (I assume for the two
attenuations). Would this be okay with the scope? Any other pointers
what to keep in mind wrt to the capacity of the probes?

Thanks.

Many good o'scope and probe tech and learning pdf's at the following
including Tektronix ABC's of probes:
http://www.ko4bb.com/cgi-bin/manuals.pl?dir=Tektronix/Tektronix_-_Probes