Vert setting | No option | 100MHz option | 20MHz BW limit | X1 probe (with 100MHz option) | X10 probe (with 100MHz option) |
200mv | 113MHz | 147MHz | 24.6MHz | 22.9MHz | 142MHz |
500mv | 170MHz | 184MHz | 25.7MHz | 22.7MHz | * |
You only need the rise time. The standard measurements use 10-90.I used 20%/80% as the step response is not OK of the rigol below 500mV/div. This means it does not have a Gaussian or flat frequency response in the 200mV range and below. To show I captured the exact same signal in both 200mV and 500mV range. The saved waveform in 500mV range I amplified to match the display in 200mV range so to make comparison easier (now you see the finite resolution also clearly).
The standard way is:Thanks I've read it. In the 500mV/div range the rise time is 1.62ns. Because of the ringing it's probably a flat response. So bandwidth would even be 450/1.62=278MHz (instead of 350/1.62=216MHz). Both really impressive for a 50MHz scope :-+
http://literature.cdn.keysight.com/litweb/pdf/5988-8008EN.pdf (http://literature.cdn.keysight.com/litweb/pdf/5988-8008EN.pdf)
For Gaussian roll off its ~0.35/Rise time; for brick wall roll off its ~0.45/Rise time.I tried but that's too much for the little rigol. It cannot do math over math.
You need only the fastest edge, because the basis of the bandwidth calculation is that of a unit impulse or Dirac delta function.
I rarely see anyone use the unit impulse alonse to measure BW because its calculation intensive. You would differentiate the impulse then apply an FFT to it, which new fast DSO can do easily:
https://community.keysight.com/community/keysight-blogs/oscilloscopes/blog/2016/09/01/how-to-measure-your-oscilloscope-and-probe-s-bandwidth-yourself (https://community.keysight.com/community/keysight-blogs/oscilloscopes/blog/2016/09/01/how-to-measure-your-oscilloscope-and-probe-s-bandwidth-yourself)
In pure math:
http://lpsa.swarthmore.edu/BackGround/ImpulseFunc/ImpFunc.html (http://lpsa.swarthmore.edu/BackGround/ImpulseFunc/ImpFunc.html)
To measure Tr accurately you need to spread it out on the screen to confirm the automated readings match the graticule readings.What is truth. Any of these measurements must be compensated for the rise time of my E-H research Model-122 pulse generator. So bandwidth of scope must even be higher.
Hope this helps. Eyeballing you graphs your data gives the DSO bandwidth as 233-300 MHz, if your measurements are true.
What is truth. Any of these measurements must be compensated for the rise time of my E-H research Model-122 pulse generator. So bandwidth of scope must even be higher.
Just to make you happy, I manually placed the cursors at the 10%/90% points and removed the falling edge. I then measure 1.5ns, but it could also be 1.6ns as that's the resolution you get.
AFAIK, the ~200MHz bandwidth on an unlocked DS1054 seems to match the measurements done previously of this scope. This scope is quite a value for the money.
[..]Do you happen to have means (and inclination ;D ) to download the measurements and perform the calculations on a PC? I'd wished I had a well-defined fast enough signal source, then I'd do it myself.
All measurements are done from the screen buffer not from the bigger capture memory. I've seen that with time and voltage measurements (up to FFT). The FTT they improved a bit by using 2400 samples from the internal buffer. Vertical resolution could be improved by averaging. That not done. Instead you get truncated vertical values, not higher resolution.
[..]
Do you happen to have means (and inclination ;D ) to download the measurements and perform the calculations on a PC? I'd wished I had a well-defined fast enough signal source, then I'd do it myself.
Do you happen to have some mercury-wetted relays for me to borrow?Do you happen to have means (and inclination ;D ) to download the measurements and perform the calculations on a PC? I'd wished I had a well-defined fast enough signal source, then I'd do it myself.
All you need to measure rise times is a mechanical switch.
(...in the 100-200Mhz range)
My message is only that the bandwidth depends (a lot) on the vertical settings that is chosen.
CH # | Sinc | Average | Risetime |
1 | On | Normal | 1.5ns |
2 | On | Normal | 2.11ns |
2 | On | Averaged | 2.09ns |
4 | Off | Normal | 4.61ns |
4 | On | Normal | 2.83ns |
4 | Off | Averaged | 4.53ns |
4 | On | Averaged | 3.34ns |
I'd use an (RF) generator and use that to determine the -3dB point. No need to derive anything from the risetime which may not be measured accurate enough.
Do you have a rough indication of how it varies and by how much?That's the information I posted when I started the thread. For a not upgraded scope the difference I find huge (+50% more bandwidth at 500mV and higher). I think indeed it has to do with amplifiers being switched in. Since they try to limit a faster intrinsic scope I would have expected a much more accurate bandwidth.
Such gain variations aren't uncommon. Sometimes it is due to a differing number series amplifiers being switched in/out, or because an analogue multipliers bandwidth is level dependent.
I'd use an (RF) generator and use that to determine the -3dB point. No need to derive anything from the risetime which may not be measured accurate enough.I don't have one at home :=\
A step response says more about the quality of the scope frontend than a single figure of merit like bandwidth or risetime.That is a different discussion. You can also choose to make a graph of the amplitude versus frequency using a levelled (or somewhat accurate) generator. Still you have to take into account that getting a signal into a 1M Ohm with (ball park) 15pf paralllel typical oscilloscope input is somewhat challenging if you want to get it absolutely right. A 50 Ohm terminator doesn't really do the trick here because the 15pf capacitor has an impedance around 100 Ohms at 100MHz.
Coudn't resist to test the DS1054Z (liberated) bandwidth the "classic" way. I'm not too sure how accurate my measurement is but the ballpark should be correct. I used the following setup: Signal source is an SSA3021X TG in zero span mode. The TG output is routed to the DS1054Z CH1 input where it is connected via a BNC T. The other side of the BNC T is routed back to the SA input by an identical BNC cable (so everything should be well terminated). I manually selected several individual frequencies and adjusted the TG output level to provide a constant reading on the SA input (within a range of +- 0.5dB). The input sensitivity on the o'scope was selected at 100mV/div. With this configuration, I found the measured Vpp to drop to 0.707 of the value at 50MHz not before I reached 299MHz!You still have a discontinuity at the scope. It's 20pF or so. So the signal from the TG reaches the scope input and sees 20pF in parallel with 50Ohm going to your SA input. That might give reflections that are frequency dependent. It will then depend on the length of your cables and the Instruments termination accuracy.
Can someone try to confirm this -- possibly cable reflections might have affected my measurements?? A similar test without TG level compensation and a 50 Ohm terminator at the "free end" of the BNC T already showed soemthing like 263MHz 3dB single channel bandwidth on my DS1054Z, so the result may also well be accurate.
Can someone try to confirm this -- possibly cable reflections might have affected my measurements?? A similar test without TG level compensation and a 50 Ohm terminator at the "free end" of the BNC T already showed soemthing like 263MHz 3dB single channel bandwidth on my DS1054Z, so the result may also well be accurate.
Many thanks, TheoB! Good to see posts from someone who (a) knows what he is doing, and (b) gives a balanced view of the DS1054Z, putting things in perspective, mentioning strengths and limitations without much fanfare.
CH # Sinc Average Risetime 1 On Normal 1.5ns 2 On Normal 2.11ns 2 On Averaged 2.09ns 4 Off Normal 4.61ns 4 On Normal 2.83ns 4 Off Averaged 4.53ns 4 On Averaged 3.34ns
CH # Sinc Average Risetime 1 On Normal 1.5ns 2 On Normal 2.11ns 2 On Averaged 2.09ns 4 Off Normal 4.61ns 4 On Normal 2.83ns 4 Off Averaged 4.53ns 4 On Averaged 3.34ns
From this good table showing effects of sampling rate on bandwidth another thing becomes evident:
Z would be a real kicker if it supported ETS. Because with ETS it would have full analog bw on all channels on repetitive signals. Did not the old models have it? DS1102* 25GSa/s, DS1052* 10GSa/s. Good stuff if you know how to use it :-+
From this good table showing effects of sampling rate on bandwidth another thing becomes evident:Yes ETS (Equivalent Time Sampling, I had to look this one up :-) ) is what my old Philips PM3320A used to have. Fine for repetitive signals. The scope had only 250Msa/s but a bandwidth of 200MHz. I must say, I'm more happy with my little Rigol. Much less noisy, smaller, real time sampling up to 1Gs, 24M deep memory, I love it :-+. Adding ETS would help in the case you need accurate timing with four channels. But that's only for risetimes/delays outside of the spec of the scope (7ns!!). So we cannot complain can we?
Z would be a real kicker if it supported ETS. Because with ETS it would have full analog bw on all channels on repetitive signals. Did not the old models have it? DS1102* 25GSa/s, DS1052* 10GSa/s. Good stuff if you know how to use it :-+
More expensive scopes might trigger before the digitizer. I think the Rigol does everything in the digital domain.
Adding ETS would help in the case you need accurate timing with four channels. But that's only for risetimes/delays outside of the spec of the scope (7ns!!). So we cannot complain can we?
This data is very interesting, but is this right, memory depth is <= 30 pts?? can confound the readings markedly. Any chance you can repeat it what you did on the link and keep memory depth consistent throughout at the highest the 1054z allows?Yes, that's just the time you see times the sample rate (5ns*12*250M=15 points from left to rigth). I indirectly choose the sample rate by enabling more channels. In vector mode it really looks ok, but that's the interpolation. Has nothing to do with samples measured :-). The two screenshots in my previous shows that more clearly.
QuoteThis data is very interesting, but is this right, memory depth is <= 30 pts?? can confound the readings markedly. Any chance you can repeat it what you did on the link and keep memory depth consistent throughout at the highest the 1054z allows?Yes, that's just the time you see times the sample rate (5ns*12*250M=15 points from left to rigth). I indirectly choose the sample rate by enabling more channels. In vector mode it really looks ok, but that's the interpolation. Has nothing to do with samples measured :-). The two screenshots in my previous shows that more clearly.
The maximum at 5ns is 5 samples per division (1Gs/s) or 60 samples per trace. But averaging helps here.
Thanks Theo, I understand. Do you know or have the published datasheet rise time of your EH 122 Pulse Generator?I just have the instrument lying around. No datasheet. Could also not find anything on the internet. It supposed to be able to generate pulses as narrow as 2ns. But I cannot measure that with the rigol scope to confirm. At work I have all the tools I could ever dream about, but at home it's just for hobby :). So I could measure it, but it's heavy and I have to carry it a long way then.
Thanks Theo, I understand. Do you know or have the published datasheet rise time of your EH 122 Pulse Generator?
Thanks Theo, I understand. Do you know or have the published datasheet rise time of your EH 122 Pulse Generator?
Even more importantly, does it have the specifications for aberrations?
One reason I have a real sampling oscilloscope is for calibrating my fast transition reference level pulse generators. Without this, a transient response and bandwidth measurement using a fast edge is of questionable accuracy. These measurements of the DS1054Z input bandwidth are not consistent with earlier measurements using a leveled signal generator and probably reflect the poor quality of the signal source.
Anyone else noticed this difference in bandwidth as a function of vertical gain?Most likely answer is that the bandwidth is limited as some amplifier is enabled for gain settings <= 200mV
QuoteAnyone else noticed this difference in bandwidth as a function of vertical gain?Most likely answer is that the bandwidth is limited as some amplifier is enabled for gain settings <= 200mV
But noticed that Sin(x)/x causes noticeable overshoot.Uhm, I guess that has been discussed to death elsewhere already :horse: and isn't specific to the DS1054Z. You might know that the signal is a square wave and hence consider the flatter graph more faithful, however given the limited sampling rate, the oscilloscope cannot know this. For the available data and input bandwidth the sin(x)/x interpolation is the most faithful representation the oscilloscope (any oscilloscope) can give you. Connecting the dots (samples) using straight lines implies higher frequency components which weren't (couldn't be) sampled or passed the input low pass filter. Showing those is kind of lying.
Uhm, I guess that has been discussed to death elsewhere already :horse: and isn't specific to the DS1054Z.
For the available data and input bandwidth
the sin(x)/x interpolation is the most faithful representation the oscilloscope (any oscilloscope) can give you
Even better: understand the math behind sin(x)/x and you'd know/understand you don't get any extra information from an excessive sampling rate where fs/2 lies beyond the range of the anti-aliasing filter.the sin(x)/x interpolation is the most faithful representation the oscilloscope (any oscilloscope) can give youMost faithful representation is given by excessive sampling rate, either RTS or ETS. Once gain - real data.
Even better: understand the math
he is making a nice video but has no idea what he is yabbering on about.
Even better: understand the math behind sin(x)/x and you'd know/understand you don't get any extra information from an excessive sampling rate where fs/2 lies beyond the range of the anti-aliasing filter.the sin(x)/x interpolation is the most faithful representation the oscilloscope (any oscilloscope) can give youMost faithful representation is given by excessive sampling rate, either RTS or ETS. Once gain - real data.
No one want old crap cheap scopes analog trigger system. These exist only in museum.
If do small home work it can easy see that Rigol Sinc is joke what can result "what ever".
Example if look Siglent and and lot of others, even old Tektronix DSO (example 2440 or 2230) draw Sinc tightly through the sample points (of course).
If do small home work it can easy see that Rigol Sinc is joke what can result "what ever".
Example if look Siglent and and lot of others, even old Tektronix DSO (example 2440 or 2230) draw Sinc tightly through the sample points (of course).
The old Tektronix 2440 series is a great example of this because it can draw the sinc interpolated signal while also highlighting the real sample points and they always line up like they should. The 2230 and 2232 however do not support sinc interpolation at all which makes sense given their relatively slow 8088 and 80C188 processors running at 20MHz/3=6.7MHz and 100MHz/7.5=13.3MHz respectively. The 2440 uses an 8MHz 6809 (system), 4 MHz 6805 (controls), and separate custom waveform processor.
If you drive the 2440 with a fast edge and do not use equivalent time sampling, then the Gibb's phenomena also shows up when sinc interpolation is used which is to be expected given a rise time to support 300 MHz operation and only a 500 MS/s sample rate.
With fast edges (or what ever waveform) as example rectangle/square wave. Corners "wobbling" is just aliasing because some harmonics in signal goes over Nyquist wall. (or better say, too near it).
I have not seen any entry level or bit over this level new digital scope what have acceptable analog side filter system. Still they design front ends like in cheap analog scopes where slow decaying gaussian BW shape is fully ok.
It is not ok in digital scopes in real time "one shot" sampling mode. (ETS is different - but only for repetitive signals). It looks like digital peoples are designing oscilloscopes and no one really care about analog front end before ADC.
Same can see in some scopes what have 50ohm input. Not even close real 50ohm impedance, exept with DC. Perhaps designer do not know what is difference between 50ohm resistance and 50 ohm impedance in case that we handle any other than DC - ELF - VLF.
Best modification is not rise analog bandwidth but reject it and/or modify bandwidth shape more steep like "brickwall" some amount under Nyquist wall. When samplerate drops, corner f need also drop.
...
With well designed analog front end and its BW shape and then perfect made Sin(x)/x interpolation there do not exist any form of signal aliasing. As long as analog BW and its shape is ok for used samplerate and signal reconstruction using Sinc.
With fast edges (or what ever waveform) as example rectangle/square wave. Corners "wobbling" is just aliasing because some harmonics in signal goes over Nyquist wall. (or better say, too near it).
With perfect sampling, the sinc filtering of a fast edge should only produce the Gibb's phenomena which is phase coherent with the input signal and looks like preshoot and overshoot. I think the actual "wobulation" sometimes seen is caused by intermodulation distortion in the digitizer which results in additional frequency spurs which are also aliased. In both cases, increasing the sample rate or bandwidth limiting the input signal helps.QuoteI have not seen any entry level or bit over this level new digital scope what have acceptable analog side filter system. Still they design front ends like in cheap analog scopes where slow decaying gaussian BW shape is fully ok.
It is not ok in digital scopes in real time "one shot" sampling mode. (ETS is different - but only for repetitive signals). It looks like digital peoples are designing oscilloscopes and no one really care about analog front end before ADC.
Some of the very early Tektronix DSOs included four pole 24dB/octave Gaussian filters which should have helped with this but I do not know if their unfiltered input bandwidth also had a 4 pole Gaussian response. On an analog oscilloscope it hardly matters except for noise measurements.QuoteSame can see in some scopes what have 50ohm input. Not even close real 50ohm impedance, exept with DC. Perhaps designer do not know what is difference between 50ohm resistance and 50 ohm impedance in case that we handle any other than DC - ELF - VLF.
Most designs implement a switchable 50 ohm feedthrough termination in front of the high impedance buffer which adds significant input capacitance compromising the 50 ohm input impedance. At 200 MHz and below this is not a problem but above that it can be; my 300 MHz 2440 handles it well enough. Some oscilloscopes route the input signal around the high impedance buffer when in 50 ohm mode like the 350 MHz Tektronix 485 and dedicated high frequency oscilloscope usually lack a high input impedance buffer.QuoteBest modification is not rise analog bandwidth but reject it and/or modify bandwidth shape more steep like "brickwall" some amount under Nyquist wall. When samplerate drops, corner f need also drop.
...
With well designed analog front end and its BW shape and then perfect made Sin(x)/x interpolation there do not exist any form of signal aliasing. As long as analog BW and its shape is ok for used samplerate and signal reconstruction using Sinc.
Except for raising the real time sample rate or using equivalent time sampling, there is no good solution for this in a time domain instrument. If the filter shape does not have linear phase, then the filter itself will effectively create the same problem which rules out filters which have higher performance in the frequency domain. The best solution I have seen is in some early Tektronix DSOs which implemented 4 pole Gaussian bandwidth filters.
IMHO there is not much use in trying to use an oscilloscope beyonds it's specifications especially a lower end one without dedicated 50 Ohm inputs. For starters there is the capacitance of the typical 1:10 probes which is a huge load for frequency components in the 100MHz region. And even if you use external 50 Ohm terminators the input capacitance of the scope will screw things up. At the end of the day you are just stacking errors on top of errors when trying to use an instrument beyond it's limits.
IMHO there is not much use in trying to use an oscilloscope beyonds it's specifications especially a lower end one without dedicated 50 Ohm inputs. For starters there is the capacitance of the typical 1:10 probes which is a huge load for frequency components in the 100MHz region. And even if you use external 50 Ohm terminators the input capacitance of the scope will screw things up. At the end of the day you are just stacking errors on top of errors when trying to use an instrument beyond it's limits.
Apply math and physics like they use the 'Josephson effect' to produce a voltage reference.IMHO there is not much use in trying to use an oscilloscope beyonds it's specifications especially a lower end one without dedicated 50 Ohm inputs. For starters there is the capacitance of the typical 1:10 probes which is a huge load for frequency components in the 100MHz region. And even if you use external 50 Ohm terminators the input capacitance of the scope will screw things up. At the end of the day you are just stacking errors on top of errors when trying to use an instrument beyond it's limits.I wonder how anybody ever built and verified the performance of the worlds highest performance scope/SA/etc :)
I wonder how anybody ever built and verified the performance of the worlds highest performance scope/SA/etc :)
Apply math and physics like they use the 'Josephson effect' to produce a voltage reference.