Products > Test Equipment
Probe into probes. What's up?
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gf:

--- Quote from: BillyO on February 01, 2023, 06:05:47 pm ---This one is 1m long, 500R.  It looks like it's suffering from a little bit of reflection.

--- End quote ---

You can try a 500R/56R divider instead of the 500R series resistor. If there is a load mismatch at the scope end of the cable, then an additional source termination of the cable helps to dampen repeated back and forth reflections. You can also check the scope's 50 Ohm input with a VNA to verify that it is really 50 Ohm and ohmic up to say 1GHz.
bdunham7:

--- Quote from: BillyO on February 01, 2023, 06:05:47 pm ---It looks like it's suffering from a little bit of reflection.

--- End quote ---

Even the P6156 has a bit of ruffling in the first part of the signal which is related to the length of the cable and so on.

Here is another comparison, the scope set for 50R vs the scope set for 1M with a 50R pass-thru terminator on the pulser.

Njk:
Sometimes, it's not only the pulse edge fidelity that matters. For floating measurements in an LV applications, I'd usually powered the scope from the battery (TDS3BAT), because using the math function for two channels would be less accurate (all the errors doubled). What is less expensive now, a battery or a super-duper floating probe?
jonpaul:
Njk:

Wideband fast measurements (as in the posts above) are seldom done on battery scopes.

In power/mains/HV work, indeed a battery operated scope is useful

The differential probes are costly and seldom needed.
In Over 50 years of work we used a simple setup:

mains>>variac>>1:1 isolation transformer

Usually a Staco or GenRad 3..20A variac and   Signal 2..5 kVa 120/240:120/240 transformer.

Then a normal grounded scope and NO diff probe.

Jon

Njk:

--- Quote from: jonpaul on February 01, 2023, 09:40:49 pm ---mains>>variac>>1:1 isolation transformer

Usually a Staco or GenRad 3..20A variac and   Signal 2..5 kVa 120/240:120/240 transformer.

--- End quote ---
Sure, but all that stuff can form a bulky setup.

I recall in a POTS line connected devices, the isolation strength requirement (between the line side and the SELV side) is of kV units, because of possible lightning strikes, etc. So in telephone modems, the common approach was to use a transformer. Later, the chips were introduced (pioneered by Silicon Labs, IIRC) that were using a capacitive digital link over an isolation barrier to communicate between the line part and the SELV part within the chip. And the last modem designs were transformer-less. I was thinking the same approach could be used to design a floating probe. Not of GHz BW, of course. A diff probe is totally different thing as it requires ground connection.
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