Electronics > Beginners
Lower bandwidth probes for a higher bandwidth oscilloscope - bad?
David Hess:
--- Quote from: tooki on December 31, 2019, 01:00:06 pm ---What's odd to me is that the Pomona datasheet for that probe (attached below) lists the probe bandwidth as being 150MHz (-3dB), but a "scope bandwidth" of 60MHz. Can someone more knowledgeable explain what they mean here??
--- End quote ---
Probes are not specified by -3 dB bandwidth. The bandwidth number is more about what maximum bandwidth will the probe support.
For instance sticking a 100 MHz probe on a 100 MHz oscilloscope does not result in a 70.7 MHz bandwidth; it results in a 100 MHz bandwidth.
Kleinstein:
It perfectly OK to have a slower probe with a fast scope if one does not need the full BW. Probes tend to have a limited life time as the thin delicate wire in the special coax tends to brake if bend too often. So it is OK to have cheap (today like 150 MHz) probes for every day use and have expensive really high BW probes only if really needed. Automatic detection of the attenuation can still be very handy.
With a modern scopes with multiple inputs one may want 2 to 4 probes anyway.
tooki:
--- Quote from: David Hess on December 31, 2019, 05:05:40 pm ---
--- Quote from: tooki on December 31, 2019, 01:00:06 pm ---What's odd to me is that the Pomona datasheet for that probe (attached below) lists the probe bandwidth as being 150MHz (-3dB), but a "scope bandwidth" of 60MHz. Can someone more knowledgeable explain what they mean here??
--- End quote ---
Probes are not specified by -3 dB bandwidth. The bandwidth number is more about what maximum bandwidth will the probe support.
For instance sticking a 100 MHz probe on a 100 MHz oscilloscope does not result in a 70.7 MHz bandwidth; it results in a 100 MHz bandwidth.
--- End quote ---
Well that's what I'd assumed. But look at the datasheet I attached above. It says 150MHz -3dB, yet it seems to be universally marketed as a 150MHz probe, not the 60MHz "scope bandwidth" the datasheet also mentions. Hence my request for someone more knowledgeable to clarify.
tautech:
--- Quote from: tooki on December 31, 2019, 07:18:29 pm ---
--- Quote from: David Hess on December 31, 2019, 05:05:40 pm ---
--- Quote from: tooki on December 31, 2019, 01:00:06 pm ---What's odd to me is that the Pomona datasheet for that probe (attached below) lists the probe bandwidth as being 150MHz (-3dB), but a "scope bandwidth" of 60MHz. Can someone more knowledgeable explain what they mean here??
--- End quote ---
Probes are not specified by -3 dB bandwidth. The bandwidth number is more about what maximum bandwidth will the probe support.
For instance sticking a 100 MHz probe on a 100 MHz oscilloscope does not result in a 70.7 MHz bandwidth; it results in a 100 MHz bandwidth.
--- End quote ---
Well that's what I'd assumed. But look at the datasheet I attached above. It says 150MHz -3dB, yet it seems to be universally marketed as a 150MHz probe, not the 60MHz "scope bandwidth" the datasheet also mentions. Hence my request for someone more knowledgeable to clarify.
--- End quote ---
And very badly advertised......specs apparently interpreted by some desk jockey ! |O
--- Quote ---Attenuation Ratio 10:1
Maximum Input Voltage CAT II¹ 300 Vrms
Scope Bandwidth MHz 60
Probe Bandwidth MHz (-3 dB) 150
System Risetime (ns) < 2.4
Probe Input Resistance (MΩ) 10
Probe Input Capacitance (pF) < 12.5
Compensation Range (pF) 15 - 40
Cable Length 4 ft. (1.2 m)
--- End quote ---
It's just a 60 MHz probe, no more, no less !
Sure if it's swept to 150 MHz it's response is -3dB but that's NOT how probes are specified ! |O |O |O
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