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x1 Oscilloscope Probe Shootout
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gf:

--- Quote from: 2N3055 on September 25, 2023, 08:28:19 am ---Best way would be to go with coax from AWG output to a T that is connected directly on BNC on reference channel set to 50Ω. Then connect a probe to that T. That creates 25Ω feed point directly on reference input channel.

--- End quote ---

The probe "sees" 25Ω, nevertheless the Vin/Vref quotient still represents the frequency response as if the probe were fed with zero source impedance, because the measured Vref is the voltage at the probe tip and not the open circuit voltage of the virtual 25Ω source. Whenever you measure Vref at the probe tip, it does not matter which source impedance the pobe can "see" during the measurement -- it cancels out.
EEVblog:

--- Quote from: 2N3055 on September 25, 2023, 08:28:19 am ---Best way would be to go with coax from AWG output to a T that is connected directly on BNC on reference channel set to 50Ω. Then connect a probe to that T.
That creates 25Ω feed point directly on reference input channel.
That is optimal way for Bode and also for waveform comparisons...
It is not important what is on output of AWG but what the reference scope channel sees..

--- End quote ---

Yes, this is the optimal way. I'll rerun these tomorrow, and maybe test some more brand probes. I'll also turn off the annoying graph autoranging.
tautech:

--- Quote from: 2N3055 on September 25, 2023, 09:21:38 am ---
--- Quote from: artur0089 on September 25, 2023, 08:49:48 am ---
--- Quote from: 2N3055 on September 25, 2023, 08:28:19 am ---Best way

--- End quote ---
use of two generator channels.
The input capacitance of X1 probes is 50-90 pF.
Without interference and distortion, T-split operates up to 2 MHz.

--- End quote ---

Bode plot works by comparing against reference chanel. It is differential measurement...

--- End quote ---
FYI, the Bode plot connection image artur0089 linked is from rf-loop in first page of his Bode Plot II thread.
It is a valid connection type once AWG channels have been copied/linked and aligned and does not require BNC Tees.
artur0089:
Amplitude +8 dB.
 :-+
2N3055:

--- Quote from: artur0089 on September 25, 2023, 10:26:53 am ---Amplitude +8 dB.
 :-+

--- End quote ---

That is just some 1x/10x 60MHz probe from old Picoscope.

Now that you mentioned it I went back and did another measurement.
But I did something else before.

Despite what people tell you that compensation trimmer should not make difference in 1x mode and is used only in 10x mode, on some probes it does stay in circuit, at least partially, or maybe simply parasitically.

Therefore I went and adjusted compensation in 1X mode for minimum peaking.  That of course completely screwed up 10x compensation but that is not important now.
Point is that I managed to change frequency response very much..
Now peak is only 3.4 dB... And -3dB point is 35 Mhz

That shows how comparison of measurement equipment, even as simple one as probes calls for lot of scrutiny, preparation and attention to detail to ensure really level playing field.

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