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x1 Oscilloscope Probe Shootout

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artur0089:
There is a mistake somewhere in the video!!!
There is no increase in frequency response!

DS2302A & DG1062Z, sine wave, sweep 0,1-30 MHz, Linear.

alm:

--- Quote from: TomKatt on September 20, 2023, 02:24:13 pm ---So I definitely should have watched Dave's video explaining 1X probes and why their BW is frequently so much lower than the 10X switched setting, where he explains that the probe cable is not regular coax but rather a specialized resistance wire designed as a lossy transmission line to help improve the higher BW on the 10X setting.  This also explains why my home-made 1X probe with generic coax performs so much better than a typical 1X/10X probe.
--- End quote ---
What makes you think reflections from the impedance mismatch at the scope and circuit ends are not a problem for 1x probes? I know Dave was a bit misleading in this video, but see page 14 and further of Tektronix Probe Circuit Concepts (1969), despite the age the most thorough thorough published resource on oscilloscope probes.

It may well be that the optimal resistance of the coax is different for 1x and 10x, but I sincerely doubt a plain 50 Ohm coax of any decent length will give good performance with a high impedance circuit. Try simulating it in something like LTspice with a fast pulse. I just measured a dedicated 1x probe (Tek P6101B), and the resistance was about 260 Ohm for the 2m version.

I don't like switchable attenuation probes just because the switch will always switch to the other setting at the worst moment and you'll spend a while messing around until you figure out it was the stupid switch, and then go out and buy dedicated 10x and 1x probes. The bandwidth of 1x probes are rarely an issue for me. If I need bandwidth, I'll use other solutions like low-Z probes (source permitting), extra amplification, active (differential) probes or other solutions. 1x probes are just the easiest / cheapest solution.

artur0089:

--- Quote from: alm on September 23, 2023, 05:41:26 pm ---Try simulating it in something like LTspice with a fast pulse.

--- End quote ---
;)
Real devices are more interesting...
Rigol PVP3150 / X10 - yellow.
Coax 50 Ohm + attenuator 50 Ohm 6 db / X15 - grey.
Delta rise/fall - +500 ps.

alm:

--- Quote from: artur0089 on September 23, 2023, 09:59:54 pm ---Real devices are more interesting...
Rigol PVP3150 / X10 - yellow.
Coax 50 Ohm + attenuator 50 Ohm / X1 - grey.
Delta rise/fall - +500 ps.

--- End quote ---
Assuming that 50 Ohm attenuator is a terminator (otherwise it's not x1), then of course it will perform well for a low impedance source. But it's irrelevant to this topic, which is about x1 high impedance probes, which are a different beast. Try using this probe on a high impedance (~kOhm) source, or with a higher voltage source, and see how it performs. The latter might burn out the terminator.

artur0089:

--- Quote from: alm on September 24, 2023, 08:39:28 am ---otherwise it's not x1

--- End quote ---
You are right, 6 dB reduces the amplitude by half, i.e. "X5".
I provided this screenshot to show the REAL operation of the equipment, and not its simulation in software.
Each probe behaves individually on a square wave.
Rigol PVP3150 is very good! FFT won't let me lie.
The signal after Rigol PVP2350 is more distorted.

--- Quote from: alm on September 24, 2023, 08:39:28 am ---with a higher voltage source

--- End quote ---
The level on the generator is the same on both measurements

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