EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: EEVblog on September 20, 2023, 12:09:31 pm
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The Rigol PVP3150 vs the Siglent PP510 oscilloscope probes in x1 mode.
Choose your fighter.
https://www.youtube.com/watch?v=EWR4RQPzB6U (https://www.youtube.com/watch?v=EWR4RQPzB6U)
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1X probes don't get the love they should get... For many tasks that don't require 10's of Mhz - such as audio, many power supplies, serial ports and even many small ucontroller testing a 1X probe can offer better resolution than a 10X probe.
My Probe Master 4901-2 1X/10X has a 1X BW of 10Mhz (love these!). The fixed 1X 4903-2 has a BW of 30Mhz (the shorter 1m cable 4903-1 goes to 38MHz). Even the DIY coax 1X clip probes I made go 20Mhz+
Seems like fixed 1X probes perform better than switchable versions.
But extremely interesting video - I was not aware the Rigol PVP3150 performs that well in 1X mode. That's impressive.
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My Probe Master 4901-2 1X/10X has a 1X BW of 10Mhz (love these!). The fixed 1X 4903-2 has a BW of 30Mhz (the shorter 1m cable 4903-1 goes to 38MHz). Even the DIY coax 1X clip probes I made go 20Mhz+
Seems like fixed 1X probes perform better than switchable versions.
Nice!
https://probemaster.com/4900-oscilloscope-probe-basic-kit-150-300-mhz/
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Rigol PVP2150/2350 also have 35MHz bandwidth in 1x mode.
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Rigol PVP2150/2350 also have 35MHz bandwidth in 1x mode.
Wow! If those are real specs those probes rival much more expensive competitors.
I wonder what the engineering trick is for getting such high BW at 1X... I'm guessing the cable capacitance plays a large part. I've noticed that the coax used on my Probe Master's is a bit thicker and more robust (but even more supple silicone) compared to most oem probes provided - which is great for production floor or rough environments.
Edit - in any event, glad to see 1X demonstrated as being much more capable than generally considered.
Edit 2 - I see the Rigol datasheet has a footnote indicating the 35Mhz BW 'Connected to an appropriate Rigol Oscilloscope'. I'm guessing the scope front end capacitance is also a factor affecting BW.
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Interesting Dave, what were the relative input capacitances on the two test probes? Wonder if they are using inductive peaking in the Rigol to extend the BW in 1X mode?
Best,
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Rigol PVP2150/2350 also have 35MHz bandwidth in 1x mode.
Wow! If those are real specs those probes rival much more expensive competitors.
I wonder what the engineering trick is for getting such high BW at 1X... I'm guessing the cable capacitance plays a large part. I've noticed that the coax used on my Probe Master's is a bit thicker and more robust (but even more supple silicone) compared to most oem probes provided - which is great for production floor or rough environments.
Edit - in any event, glad to see 1X demonstrated as being much more capable than generally considered.
Edit 2 - I see the Rigol datasheet has a footnote indicating the 35Mhz BW 'Connected to an appropriate Rigol Oscilloscope'. I'm guessing the scope front end capacitance is also a factor affecting BW.
The retail price of PVP2150 in China is 185 yuan (equivalent to about 25 US dollars), and its selling point is the bandwidth in 1x mode.
Many sellers are selling the PVP2150/2350 separately, and no one mentioned that it needs to be used with a Rigol's scope to achieve the claimed bandwidth, so I guess it should work with other brands.
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Many sellers are selling the PVP2150/2350 separately, and no one mentioned that it needs to be used with a Rigol's scope to achieve the claimed bandwidth, so I guess it should work with other brands.
I'm sure that it does. Although I don't believe I've ever encountered an issue using different probes, I have read that certain probes can sometimes not play well with equipment it wasn't designed for because of impedance mismatches. But I suspect most of the scopes in this range have similar enough parameters that these probes would work fine.
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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.
Which begs the question - are better 1X BW probes like these Rigol examples mentioned here using conventional coax cable, with other engineering design elements negating the need for the resistive lossy wire used in more conventional 1X/10X probes? Perhaps materials and cable technology have evolved since Tek developed the lossy cable design so many years ago? It seems like their 1X 30Mhz+ BW is very similar to straight coax. But if this can be done, I wonder why high BW 1X/10X probes are so rare?
]https://www.youtube.com/watch?v=OiAmER1OJh4] (https://www.youtube.com/watch?v=OiAmER1OJh4)
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Edit 2 - I see the Rigol datasheet has a footnote indicating the 35Mhz BW 'Connected to an appropriate Rigol Oscilloscope'. I'm guessing the scope front end capacitance is also a factor affecting BW.
I think the footnote applies to both bandwidth specs (x1 and x10). The footnote indicator is coincident with the Chinese text for "Bandwidth" and they simply didn't bother also putting it on the English translation.
My guess is that they say the specs apply only when used with Rigol scopes because that they don't want to be bothered with complaints from or supporting people using them with other scopes or with people complaining that they don't get 350MHz bandwidth when they plug their PVP2350's to a DS1054Z (I'm certain this happens more often than you might guess).
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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.
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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.
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) (https://www.pearl-hifi.com/06_Lit_Archive/02_PEARL_Arch/Vol_16/Sec_53/Tek_Circuit_Concepts/Probe_Circuits_11_69.pdf), 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.
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Try simulating it in something like LTspice with a fast pulse.
;)
Real devices are more interesting...
Rigol PVP3150 / X10 - yellow.
Coax 50 Ohm + attenuator 50 Ohm 6 db / X15 - grey.
Delta rise/fall - +500 ps.
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Real devices are more interesting...
Rigol PVP3150 / X10 - yellow.
Coax 50 Ohm + attenuator 50 Ohm / X1 - grey.
Delta rise/fall - +500 ps.
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.
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otherwise it's not x1
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.
with a higher voltage source
The level on the generator is the same on both measurements
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The performance of a x1 probe may depend on the input impedance of the scope. The can make a difference in the response and if one sees a slight peaking or not. Also the signal source impedane can make a difference.
I would expect the switchable x1 / x 10 probes to be some compromise and fixed probes may be a bit better. On the low price end it looks like that one mainly gets the switchable ones.
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The Rigol PVP3150 vs the Siglent PP510 oscilloscope probes in x1 mode.
Choose your fighter.
https://www.youtube.com/watch?v=EWR4RQPzB6U (https://www.youtube.com/watch?v=EWR4RQPzB6U)
Nice video...but...but... absolutely essential informations are missing, so evaluating whether the received data is bullshit or whether it even has any value other than entertainment.
Or is this some kind of "engineer joke".
How you have connected signals (exactly) and how you have setup BodePlot. Is it displaying/measuring Vin/Vout or Vout.. (I do not know how these settings are in R&S
Think example possible VSWR effect. If Bode measure Probe in and then compare it to Ref In (after this coaxial (mismatch to 1M input) and after this other mismatch done with T split to probe input.
It has also been completely forgotten that according to normal practice Probes are classified by measuring the 25ohm source impedance.
So nearly all possible mistakes have been made carefully.
Look your generator output where is connected Probe input using T for split it to Probe and then to coaxial what goes to Bode Reference.
Now if Bode is on Vin/Vout mode signal in probe input is totally other than signal in reference input point... except when signal is very low freq or DC.
Also @artur0089 test may give some reason for thinking...
This is bit alarming in this video. Is this really engineer made test setup what is partially visible here:
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I've only ever owned or used 1 AWG, my SDG2142X. So sometimes when I'm looking at distortions on my scopes, IDK if it comes from the AGW, the probes, or the scopes. Sometimes at higher frequencies I'm sure it's the probes, and reflections. But it makes me wonder what the AWG really outputs sometimes.
But looking at the prices of them, for now I should just get more suitable probes and coax accessories.
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Problem found! The signal swing in the reference cable is reduced.
DS2302A & DG1062Z, sine wave, sweep 0,1-30 MHz, Linear.
Coaxil - blue.
Rigol PVP3150 - yellow.
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T-split - evil!..
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Think example possible VSWR effect. If Bode measure Probe in and then compare it to Ref In (after this coaxial (mismatch to 1M input) and after this other mismatch done with T split to probe input.
It has also been completely forgotten that according to normal practice Probes are classified by measuring the 25ohm source impedance.
So nearly all possible mistakes have been made carefully.
Look your generator output where is connected Probe input using T for split it to Probe and then to coaxial what goes to Bode Reference.
Now if Bode is on Vin/Vout mode signal in probe input is totally other than signal in reference input point... except when signal is very low freq or DC.
If the probe tip is attached to one leg of the T, and the other leg goes via coax to the (50 Ohm) reference input, then the reference input "sees" the same voltage as the probe tip (delayed by the cable length). Ideally, there won't be significant reflections from the scope back to the T (unless the 50 Ohm input is crap). The voltage at the T is of course not the same as the generator voltage, nevertheless Vin/Vref is the probe's frequency response. But indeed, the source impedance cancels out and the frequency response is measured as if source impedance were zero, i.e. the loading of the circuit by the probe is not considered.
In order to measure the frequency response including a 25 Ohm source resistance, I think the following configuration should work:
Feed the generator output into the input of a 2-resistor power splitter. Connect one output leg of the power splitter to the (50 Ohm) reference input and attach a T to the other output leg of the power splitter. Attach the probe tip to the 2nd leg of the T and terminate the 3rd leg of the T with 50 Ohm. Then the voltage at the probe tip is suposed to be VRef*Zin/(Zin+25), where Zin is the input impedance of the probe, i.e. a 25 Ohm source resistance is included in the measured frequency response.
Look your generator output where is connected Probe input using T for split it to Probe and then to coaxial what goes to Bode Reference.
Now if Bode is on Vin/Vout mode signal in probe input is totally other than signal in reference input point... except when signal is very low freq or DC.
I think you are right, I needed to use a x10 high bandwidth probe here. I'll re-run it and see what I get.
EDIT: I quickly re-ran it and there was little difference.
I don't see how a high-Z probe for the reference measurement would make a significant difference (it rather introduces additional unceretainty, due to its own frequency response). Regardless how you measure the voltage at the probe tip and use it as Vref, you measure the probe's frequency response as if source impedance were zero.
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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..
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Best way
use of two generator channels.
The input capacitance of X1 probes is 50-120 pF.
Without interference and distortion, T-split operates up to 2 MHz.
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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.
:-//
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Best way
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.
Bode plot works by comparing against reference chanel. It is differential measurement...
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Output of AWG is connected to T in CH1. CH1 is set for 50Ω. in other side of T you connect probe and connect probe's BNC to CH3.
In Bode plot you setup CH1 as reference channel and CH3 as output.
Whatever distortion in amplitude and phase happens at T compared to output of AWG is irrelevant.
Bode plot measures phase between CH1 and CH3, not relative to AWG...
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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.
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.
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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..
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.
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Best way
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.
Bode plot works by comparing against reference chanel. It is differential measurement...
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.
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Amplitude +8 dB.
:-+
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Amplitude +8 dB.
:-+
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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Best way
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.
Bode plot works by comparing against reference chanel. It is differential measurement...
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.
I remember. He used this setup with DUT that has 50Ω impedance inputs itself and not probe testing. In addition to that he does say to use it only on low frequencies.
With Bode test we are not concerned with fact that signal from AWG will get amplitude or phase variations. We only need to ensure reference channel sees exactly the same signal as DUT as much as possible.
It is relative measurement.
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Here you go, tests re-run with practically the same results as my original video.
CH1 ref input 50ohm terminated, and CH2 probe to BNC adapter on a CH1 T-piece.
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4 more probes, part numbers in the annotation on screen.
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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.
Why, if everything has been tested and proven a long time ago?
And, most importantly, it complies with the schedule from the manufacturer!
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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.
Why, if everything has been tested and proven a long time ago?
And, most importantly, it complies with the schedule from the manufacturer!
So why are you measuring probes if you already know what manufacturer said?. What is the point of the topic ? ^-^
Take one of those 1x10x probes and experiment with compensation trimmer and see how depending of how probe is set will change response.
With 1x or 10x fixed probe it will also differ which scope are using it for too...
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Keysight distinguishes two different frequency responses of a probe (https://prc.keysight.com/Content/PDF_Files/3121-1312.pdf)
- The response with respect to the probe tip voltage as the probe loads the circuit (which is independent of source impedance)
- The response with respect to the voltage at the probe point as if the probe is not there (assuming 25 Ohm source impedance)
Nobody here seems to consider #2 :-//
(Only rf-loop mentioned "according to normal practice Probes are classified by measuring the 25ohm source impedance" which suggests that he did mean to the latter one.)
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So why are you measuring probes if you already know what manufacturer said?
Trust but check!
What is the point of the topic ? ^-^
Bode plot on this Rohde & Schwarz - not everything is clear...
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Keysight distinguishes two different frequency responses of a probe (https://prc.keysight.com/Content/PDF_Files/3121-1312.pdf)
- The response with respect to the probe tip voltage as the probe loads the circuit (which is independent of source impedance)
- The response with respect to the voltage at the probe point as if the probe is not there (assuming 25 Ohm source impedance)
Nobody here seems to consider #2 :-//
(Only rf-loop mentioned "according to normal practice Probes are classified by measuring the 25ohm source impedance" which suggests that he did mean to the latter one.)
That is something different.
Probe will, by virtue of it's own electrical characteristics, when connected into a circuit, become part of the circuit.
This means that connecting the probe will change voltages, phases, resonant frequencies, currents and whatever in that part of circuit you connected a probe to. That is reason why you cannot measure accurate frequency or sometimes measure at all crystal oscillators etc.. etc.
In some Keysight scopes, they have a software correction mode (Source Estimate) that by presuming 25Ω source impedance it artificially "removes" loading, i.e. it approximates what loading and signal distortion probe caused when connected and tries to approximate how signal looked before. It does that by presuming clean 25Ω resistive source impedance and by knowing what that particular probe loading looks like.
The fancy sounding "True View" is just like normal probe view on every oscilloscope.
This is remotely related to topic here but not relevant. Good read though.
Problem with probes is this:
1. Probes load circuit. By doing that they change real signal in different degrees and levels.
2. Amount of signal "degradation" will depend on signal source impedance and source impedance characteristics.
3. Then we have probe's own transfer function, the measure of how signal on input relates to signal on output, as consequence of it's electrical schematics.
4. Scope input also presents complex schematic but lets pretend that probe output and scope input are already married in probe's electrical schematic to simplify things because probe is supposed to be used that way and this works for us in this case.
5. Combine all of that.
To make possible to have at least some kind of way to compare probes, standardization bodies made standard to test probe BW with 25Ω source impedance. A terminated 50Ω generator. That allows for some kind of comparison but BW measured that way will not correspond with frequency response of probe when connected to any kind of other circuit.
If you connect probe to high impedance source, your BW will be dominated by RC filter (or RLC if source is inductive) created from source impedance and shunting capacitance of probe's tip.
One other way to measure probe is with a Bode plot. But that introduces another complication. Namely, Bode plot will plot phase/gain frequency response, but will REMOVE loading to the signal source by the probe. How? Because it will measure delta, difference, between input and output signal as a ratiometric measurement, compensating for changes in input signal.. In effect, it will provide result of measurements as if source impedance of generator was 0Ω. Of course it is not ideal, but as long loading is within dynamic range of inputs it won't care.
Huh? So no more answers but more questions...
So what do we conclude form this?
One example: audio power amplifiers or power supplies have very low impedance on their outputs for instance. When measuring those, your probe will behave similar to Bode plot (with added benefit that you will also know phase response of the probe).
If you wanted to measure on 600Ω system (audio) you would be prudent to insert impedance converter between your AWG and probe and run a frequency sweep with 600Ω impedance, characterizing it for that use...
I just tried now and with paralleling terminators I dropped source impedance to 12.5Ω. -3dB pint raised from 24MHz to 28 Mhz.
So when measuring some PSU output for ripple or noise, in usual 20MHz BW for that purpose, my simple 60MHz(10x) rated at 6Mhz when 1x will comfortably and accurately perform that task.
Everything else will be anybody's guess...
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Probe will, by virtue of it's own electrical characteristics, when connected into a circuit, become part of the circuit.
This means that connecting the probe will change voltages, phases, resonant frequencies, currents and whatever in that part of circuit you connected a probe to. That is reason why you cannot measure accurate frequency or sometimes measure at all crystal oscillators etc.. etc.
Sorta the Heisenberg Uncertainty Principle in our field, anything and everything you measure is fundamentally "Wrong", how Wrong depends on many factors!! Thus, we must attempt to minimize the things that influence the measurements towards more Wrong!!
Best,
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The fewer add-ons, the more truthful the result.
Sweep generator - probe - oscilloscope.
Newfangled things are harmful when they are in large quantities.
Take one of those 1x10x probes and experiment with compensation trimmer and see how depending of how probe is set will change response.
The changes were ±2 MHz.
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Why didn't Rigol implement Bode in his previous generation instruments, following the example of Siglent?
The question is rhetorical.
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Why didn't Rigol implement Bode in his previous generation instruments, following the example of Siglent?
The question is rhetorical.
You are wrong, non rhetorically...
They did, and it was a complete joke.
And answer is that Siglent and Rigol seem to have different product strategy.
Respectfully, how is this relevant to the discussion about probes?
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The topic was created based on a video, in which Dave does something that no manufacturer has advertised in their devices.
And what? A complete failure, both in amplitude and phase! Results at frequencies above 15 MHz are unstable and cannot be cloned.
Siglent has a great idea, to use both channels of the generator. I don't have such a kit and can't check it.
All that remains is to regret the “support” of the software from Rigol.
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By the way, if anyone wants to make a Bode plot using the Siglent kit, using two generator channels.
The Rigol DG1000Z comes with only one 50 Ohm coaxial cable.
But, “an old warrior is a wise warrior”...
Immediately, I bought a pair of identical cables on AliExpress. Above, a comparison at 40 MHz, with them. The phases coincided at 0 degrees.
Below is a comparison of the original one (yellow) and the purchased one (blue). The difference in length is 10 mm, the original one is shorter. Length 1120 mm.
Which one is more correct?
Up to 15 MHz the difference is unnoticeable.
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Manually, from two generator channels.
At each frequency, I calibrated the phase and signal level.
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Nice video...but...but... absolutely essential informations are missing, so evaluating whether the received data is bullshit or whether it even has any value other than entertainment.
Or is this some kind of "engineer joke".
How you have connected signals (exactly) and how you have setup BodePlot. Is it displaying/measuring Vin/Vout or Vout.. (I do not know how these settings are in R&S
Think example possible VSWR effect. If Bode measure Probe in and then compare it to Ref In (after this coaxial (mismatch to 1M input) and after this other mismatch done with T split to probe input.
It has also been completely forgotten that according to normal practice Probes are classified by measuring the 25ohm source impedance.
So nearly all possible mistakes have been made carefully.
Look your generator output where is connected Probe input using T for split it to Probe and then to coaxial what goes to Bode Reference.
Now if Bode is on Vin/Vout mode signal in probe input is totally other than signal in reference input point... except when signal is very low freq or DC.
Also @artur0089 test may give some reason for thinking...
This is bit alarming in this video. Is this really engineer made test setup what is partially visible here:
Is there a tutorial on how to do this test properly?