Scope probes

[mansr]

Below are scope screenshots showing the same signal measured using four different probes ranging in price from £50 to £3k.

 

[LTig]

I would prefer the last, or the first if the last is £3k.

What is the source of the signal?

 

[amirm]

Off-topic but you can get very high bandwidth probes for Tek on ebay. I purchased a brand new, 1 GHz one from Singapore I think for a fraction of Tek price. I think they are buying four channel high end scopes and then selling off some of the probes that come with them.

 

[PierreV]

Is that what golden eared audiophiles have been trying to tell us for ages?

tbh, I did not expect such an impact

 

[sergeauckland]

Even the best of those traces looks worse than my old Hitachi 'scope with a £10 probe.

S.

 

[mansr]

I would prefer the last, or the first if the last is £3k.

What is the source of the signal?

The source isn't important. It's not some fancy audiophile clock if that's what you were wondering.

The probes are from top to bottom, TPP0100 (£50), TPP0250 (£280), TPP0500B (£459), and TAP1500 (£3k).

 

[mansr]

Off-topic but you can get very high bandwidth probes for Tek on ebay. I purchased a brand new, 1 GHz one from Singapore I think for a fraction of Tek price. I think they are buying four channel high end scopes and then selling off some of the probes that come with them.

I got the TAP1500 probe off eBay from someone in the UK for a small fraction of the list price. It was practically unused, the accessories kit never opened.

 

[mansr]

Even the best of those traces looks worse than my old Hitachi 'scope with a £10 probe.

Depends on what the signal actually looks like. I doubt it's a perfect square wave to begin with.

 

[LTig]

The source isn't important. It's not some fancy audiophile clock if that's what you were wondering.

I just wanted to know what you used so I can repeat the test with my DSO. The only square signal source I have at hand is the 1 kHz test signal of the scope for adjusting the probe compensation cap. I think about buying a signal generator and the current favorite is the Siglent SDG1062X (60 MHz max) with a rise time of 4.2 ns. Your source seems to have half that risetime though, if I interpret the screenshot correct.

The probes are from top to bottom, TPP0100 (£50), TPP0250 (£280), TPP0500B (£459), and TAP1500 (£3k).

Exactly what I feared ...
Well I have to check my probes, they are certainly much cheaper than £50, the whole scope with 2 probes (Siglent SDS1202X-E) was € 340 with free shipping ...

 

[sergeauckland]

Depends on what the signal actually looks like. I doubt it's a perfect square wave to begin with.

Yes, but the last one looks more or less OK as a square wave, so why don't the others? Nos 2 & 3 look particularly poor. If my cheap £10 probe can render a 'perfect' square wave, why do 2 & 3 look so poor? What are they doing? Makes no sense to me. Were they properly equalised?

S

 

[LTig]

Yes, but the last one looks more or less OK as a square wave, so why don't the others? Nos 2 & 3 look particularly poor. If my cheap £10 probe can render a 'perfect' square wave, why do 2 & 3 look so poor? What are they doing? Makes no sense to me. Were they properly equalised?

The first one just has lower bandwidth. #2 and #3 look broken though.

 

[mhardy6647]

What's the fundamental frequency of the square wave? I could figure it out, but I am very lazy.
The source might be important -- do you (the OP) know that it's a 'clean' square wave source at -- whatever fundamental frequency is being used.

I am kind of surprised and saddened by the apparent performance of those probes for the prices listed.

 

[SIY]

Were these adjusted 10x probes?

 

[mansr]

What's the fundamental frequency of the square wave? I could figure it out, but I am very lazy.

Too lazy to read? It's written at the bottom of each screenshot: 24.5758 MHz.

The source might be important -- do you (the OP) know that it's a 'clean' square wave source at -- whatever fundamental frequency is being used.

The source is the clock output an S/PDIF receiver with a series resistor. With the TPP0500B probe before the resistor, it looks like this:

Were these adjusted 10x probes?

The probes are all 10x. The passive ones were all compensated, the fancy ones automatically. The TAP1500 active probe doesn't have such a setting.

 

[spacevector]

What scope are you using OP? Some of these probes may have specific models they work with. Also, did you compensate the probes? For example, the compensation procedure for TPP0500B lifted from the manual: https://www.tek.com/passive-probe-manual/tpp0250-tpp0500b-1

Compensating the probe
You should compensate the probe after you attach it to an
oscilloscope for the first time, or after you have changed
the probe tip cartridge.
1. Connect the probe to an oscilloscope channel.
2. On MSO/DPO5000 instruments:
a. Connect the probe to the probe compensation output
terminals on the oscilloscope front panel.
b. Select Vertical > Probe Cal....
c. Select the channel number tab of the channel that you
connected the probe to.
d. In the Calibration section, click Calibrate Probe.
On MDO3000 and MDO/MSO/DPO4000B instruments:
a. Press the Channel Menu front panel button for the
channel that you connected the probe to.
b. Push the More button until Probe Setup is selected.
c. Push the Calibrate Probe button and follow the
on-screen instructions.
If the probe compensation fails, verify that the signal
and ground connections are secure at the Probe Comp
connections on the oscilloscope. Also check that the ground
connection is secure at the probe head, the rigid or pogo
tip is secured tightly in the pro

 

[mansr]

If my cheap £10 probe can render a 'perfect' square wave, why do 2 & 3 look so poor?

I doubt your cheap probe can measure a rise time of less than 2 ns, which is what we're looking at here. The distortion is probably the result of interactions between the probe capacitance, source impedance, and PCB + probe ground inductance.

 

[pkane]

Picoscope stock (i.e., cheap) 10x probe. 1MHz, 50kHz, and 1kHz square wave (built-in signal generator):

 

[mansr]

What scope are you using OP? Some of these probes may have specific models they work with. Also, did you compensate the probes?

It's a Tek MDO3054. The TPP0250 and TPP0500B are both sold together with this range of scopes. As I already said, the probes are compensated according to instructions. It's not exactly a difficult procedure.

 

[LTig]

OK, here is my probe (Siglent PP215, 200 MHz) connected to the 1 kHz square generator of the DSO (Siglent SDS 1202X-E, 2 x 200 MHz) in 10:1 mode, proper compensated.

200us per div:

500 ns per div:

10 ns per div :

Oops. Seems the square generator is not the squarest one. Risetime of almost 1 us ...

 

[mansr]

Picoscope stock (i.e., cheap) 10x probe. 1MHz, 50kHz, and 1kHz square wave (built-in signal generator):

View attachment 53698 View attachment 53700 View attachment 53699

That's a much longer rise time. Here's my scope's built-in AFG with the TPP0500B probe showing a rise time of about 4 ns: