Rigol DHO800 memory depth / bandwidth upgrades and noise level! - Page 1
Forum section: electronics / testgear

author: Bob773
author_rank: Newbie
timestamp: November 06, 2023, 03:04:55 am
content: It seems like nobody is talking about how the memory depth cuts back when adding channels… goes from 25Mpts single channel to 10Mpts with 2 channels, why not 12.5?… then drops to 1Mpts with 3/4 channels?!! This alone is a major deal breaker for me. I use single triggers with multiple channels very often. Anybody have insight to why this would be?

author: PELL
author_rank: Regular Contributor
timestamp: November 06, 2023, 04:25:38 am
content: https://www.eevblog.com/forum/testgear/hacking-the-rigol-dho800900-scope/msg5148330/#msg5148330follow this guide hack the mem-depth, then you can get 10M at 4 channelsI tested it under firmware 1.01 and it works to me

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 09:14:18 am
content: Quote from: Bob773 on November 06, 2023, 03:04:55 amWe've all hacked ours to 50Mpts so we get 10Mpts per channel with all 4 channels on.That's why it doesn't get much discussion - it's a non-issue!All you need is an Ethernet cable...PS: While you're doing that "upgrade" you can also change the bandwidth of a DHO804 to 200MHz (measured).

author: csuhi17
author_rank: Frequent Contributor
timestamp: November 06, 2023, 09:53:38 am
content: Yes, but why do we lose 21M of memory on the 800 and 10M on the 900?

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 10:40:47 am
content: Quote from: csuhi17 on November 06, 2023, 09:53:38 amAll we know is that it's a marketing decision not a hardware thing.

author: magic_smoke
author_rank: Newbie
timestamp: November 06, 2023, 11:09:25 am
content: Quote from: Fungus on November 06, 2023, 09:14:18 amIs there a downside to these upgrades? That goes against the official maximum bandwidth (100Mhz) afaik.

author: ebastler
author_rank: Super Contributor
timestamp: November 06, 2023, 12:05:59 pm
content: Quote from: magic_smoke on November 06, 2023, 11:09:25 amIt is the "nominal 100 MHz" bandwidth. Turns out the actual bandwidth of the scope's front end is larger than stated.(Which is good and bad -- you need to be a bit more careful about potential aliasing when using the scope in 4-channel mode, i.e. with only 312 MSa/s.) The early DHO800 firmware even had a provision for an "official" bandwidth upgrade, but it has apparently disappeared with the more recent firmware release. I don't think anybody has reported side effects beyond the potential aliasing -- which should apply to the unmodified DHO814 as well.There is also an alternative hacking approach which lets the DHO800 think it is a DHO900, which would potentially enable even higher bandwidth. But this comes with side effects, namely offset error (at least in some units) which don't go away upon auto-calibration. It also displays the digital channel control in the bottom row of the screen, which remains non-functional of course because some hardware is missing in the DHO800. Hence, this is not a recommended way to "upgrade" your scope at this time.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 01:31:12 pm
content: Quote from: ebastler on November 06, 2023, 12:05:59 pmYep. I've had my DHO804 up to 280Mhz measured bandwidth.Quote from: ebastler on November 06, 2023, 12:05:59 pmI'm sure that's fixable with a bit more hacking, but... 200MHz is enough for me.

author: Warhawk
author_rank: Frequent Contributor
timestamp: November 06, 2023, 01:42:51 pm
content: Do I get it right that to get the extra memory you need to make the scope thinking that it is the 900 series?

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 02:02:37 pm
content: Quote from: Warhawk on November 06, 2023, 01:42:51 pmNo.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 02:05:43 pm
content: I'm sure this question is going to be asked a million times over the next few years so I'll put this here as a reference.My 'scope says "DHO804" on the front. I've modified the bandwidth and memory options.Here's my new "About" screen:Here's my new "Options" screen:Here's my new memory depth with 4 channels enabled:Here's my measured bandwidth:nb. I'm using the bandwidth math fromhereand Martin72 confirmed the "100Mhz" bandwidth with a 200Mhz sine wavehere.(I don't have a SIGGEN that goes that high so I can only do rise times)All changes are harmless and 100% reversible. There are NO side effects.Notice the difference in rise time and the shape of the yellow waveform between the last two images. That's because 321.5MSa/s isn't enough for a 197Mhz 'scope, ie. I'm seeing some aliasing.(Solution: (a) Be aware, and (b) Turn off some channels when viewing fast signals and see if anything changes. If it does? Aliasing!)

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 02:23:09 pm
content: I just removed my bandwidth upgrade (proof that it's reversible!):Now my measured bandwidth is 128MHz:I have no idea where Rigol get their "70Mhz" from... but don't complain!

author: Warhawk
author_rank: Frequent Contributor
timestamp: November 06, 2023, 03:24:49 pm
content: Thanks, I lost interest in the other thread when it went off-topic with the gibbs' ears. I did not know that there is generally an option for extended memory. I found it now. I am happy for you and others. This was really annoying limitation.

author: ebastler
author_rank: Super Contributor
timestamp: November 06, 2023, 03:27:59 pm
content: I am wondering whether the 0.45 factor to convert risetime to bandwidth is a bit too aggressive here. Historically a factor of 0.35 has been used, which I understand is correct for simple 1- or 2-pole bandwidth limiting filters. The recent transition to 0.45 is justified when steeper, higher-order filters are used for bandwidth limiting.But looking at the nice step response of the DHO800, without overshoot and ringing, I would assume that it uses a relatively "soft" lowpass filter. So maybe the classical factor of 0.35 is closer to the truth here? It would put the bandwidth closer to Rigol's specs.Anybody here with access to a tunable sine wave generator which goes up to 200 MHz to measure the bandwidth in the frequency domain? And ideally an even higher bandwidth scope to check the generator output amplitude?

author: Warhawk
author_rank: Frequent Contributor
timestamp: November 06, 2023, 04:17:35 pm
content: Quote from: ebastler on November 06, 2023, 03:27:59 pmI do have the access but don't have the scope

author: TomKatt
author_rank: Frequent Contributor
timestamp: November 06, 2023, 04:29:44 pm
content: I'm a bit surprised the shared DAC and 312smps at 4 channels isn't more of a concern.

author: Serg65536
author_rank: Regular Contributor
timestamp: November 06, 2023, 04:53:17 pm
content: Quote from: TomKatt on November 06, 2023, 04:29:44 pmIt's NOT a DAC, but ADC!And you are right:250 Msampl/s, as other brands have at a slightlyhigher pricesis much better! And don't forget aboutnoise and quantization step: it's also much higher in competition. So yee.. it's not a good scope...

author: TomKatt
author_rank: Frequent Contributor
timestamp: November 06, 2023, 04:55:53 pm
content: Yes ADC - duh. The DST time shift always puts me off.And I didn't mean to infer the lack of dual ADC's made it unusable, only that sampling rate seems to be an otherwise high priority spec.

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 05:08:59 pm
content: Quote from: Serg65536 on November 06, 2023, 04:53:17 pmIt is not an absolute value competition, but Sample rate / BW combination.If you have 130 MHz -3db BW and 312.5 MS/s then it is fine.If you have 200 MHZ BW and 312 MS/s you are undersampling.What other scope are you refering to specifically?

author: ebastler
author_rank: Super Contributor
timestamp: November 06, 2023, 05:12:53 pm
content: The ADC sample rate has been discussed at some length -- I don't recall in which of the various DHO800/900 threads.The unusual thing with those scopes is that it isnotthe ADC which limits the acquisition rate, but apparently the FPGA or the FPGA/DRAM interface. The same ADC runs at 2 GSa/s in the DHO1000, but only 1.25 GSa/s in the 800/900. And when one activates the digital channels in the DHO900, the ADC even falls back to 625 MSa/s in total -- shared across 1 to 4 channels depending on the setup. The latter fact is unfortunately not disclosed in Rigol's datasheet.So yes, there are tradeoffs which one needs to be aware of. And the advertised 250 MHz bandwidth in the DHO924 is pushing things a bit far for my taste. But overall, it's still a very nice package, even with the logic anaylzer enabled. Compare the acquisition rates with a Saleae Logic Pro 16, for example. (And compare the price tag too.)

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 05:17:01 pm
content: Quote from: ebastler on November 06, 2023, 03:27:59 pmYes, and 0.45 works!https://www.eevblog.com/forum/testgear/hacking-the-rigol-dho800900-scope/msg5132343/#msg5132343

author: ebastler
author_rank: Super Contributor
timestamp: November 06, 2023, 05:31:37 pm
content: Quote from: Fungus on November 06, 2023, 05:17:01 pmThanks! That is good news indeed -- and on the other hand a call to paying some attention to aliasing.I just notice that you had already mentioned Martin's measurements a few posts earlier. I had overlooked the further text below the pictures there, sorry.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 05:37:24 pm
content: Quote from: TomKatt on November 06, 2023, 04:29:44 pmIt is what it is. Just be careful and switch off a channel or two if there's any doubt.You're also free to leave it at Rigol's "70Mhz" if you want to - 128Mhz is still a decent bandwidth and the 'scope is still a bargain for $399.nb. You can switch between 70Mhz/100Mhz options in under a minute. The longest part is waiting for it to reboot.

author: voltsandjolts
author_rank: Unknown
timestamp: November 06, 2023, 05:42:25 pm
content: Perhaps leaving the bandwidth at 70MHz (128MHz actual, apparently) reduces scope noise, compared to 100MHz (200MHz actual, apparently)? I haven't seen anyone posting measurements of ENOB before/after upgrade.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 06:23:25 pm
content: Quote from: voltsandjolts on November 06, 2023, 05:42:25 pmLeaving it at "70Mhz" is a very sensible option if you often work with four high speed signals or simply want the best possible signal fidelity.I can easily measure noise before/after. Hang on...

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 06:57:04 pm
content: The results are in. Here's the RMS noise level of both bandwidth options, with and without bandwidth limiter, nothing connected to the inputs.There's surprisingly little difference, only about 5%. I repeated it three times just to be sure, I honestly expected more.

author: voltsandjolts
author_rank: Unknown
timestamp: November 06, 2023, 07:01:20 pm
content: I see two screenshots, both at 20MHz bandwidth, showing same noise as expected.When you say 'nothing' on the inputs, do you mean floating inputs, or 50 Ohm terminated inputs?

author: ebastler
author_rank: Super Contributor
timestamp: November 06, 2023, 07:05:33 pm
content: Quote from: voltsandjolts on November 06, 2023, 07:01:20 pmLook at channel 2.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 07:16:03 pm
content: Quote from: voltsandjolts on November 06, 2023, 07:01:20 pmThere's two channels on each...Floating inputs.

author: Serg65536
author_rank: Regular Contributor
timestamp: November 06, 2023, 07:17:41 pm
content: Quote from: TomKatt on November 06, 2023, 04:55:53 pmI've got you wrong, sorry.Yes, BW to SR ratio is not good here.But it's always nice to have the ability to capture a signal with the maximum available BW and full 1.25 GS/s.IMHO, it's more disappointing to have very high noise due to 8 GS/s ADC, and use an oscilloscope below 100 MHz on daily basics.

author: ebastler
author_rank: Super Contributor
timestamp: November 06, 2023, 07:33:40 pm
content: Quote from: Fungus on November 06, 2023, 06:57:04 pmThe lack of difference might be due to the fact that decimated screen data are used for the RMS calculation? (I.e. the decimation acts as another bandpass filter.)How do the results change if you change the timebase? Also, doesn't the vertical amplification go up to 500 µV/div -- does that change the result?

author: iMo
author_rank: Super Contributor
timestamp: November 06, 2023, 07:37:46 pm
content: Store the data in the .csv and make the rms calc in the excel, for example.The 40uV rms noise means aprox 270uVpp - that is what you should see on the screen then..Also to measure noise with the open inputs is not the best approach, imho.

author: voltsandjolts
author_rank: Unknown
timestamp: November 06, 2023, 08:02:05 pm
content: Floating inputs are random number generators, use 50 Ohm termination.

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 08:17:24 pm
content: You cannot measure noise on 1µs/div. You are high-pass filtering low frequencies out. Pretty much all of the 1/f noise which is actually large part of noise in scope amps..Set scope at 1 ms/div, 1mv/div, and NO 20 MHz BW limiter.To see what is actual noise with 100 MHz BW.Then repeat with 20 MHz limit.And if you look at your stats, you have very large difference between max and min AC RMS value.This is the point where you reset stats and see again. If you again accumulate have such a large difference between max and min AC RMS something is wrong.Make sure to put a non shorting cap (or wrap a piece of aluminium foil over BNC) on input so there is not induced voltage.Shorting input with 50 Ω is not going to show what noise is with 1MΩ inputs but less, which is not what you going to see with passive probes connected.Whenever i have shown any data from any scope that is how it's done.50Ω measurements are separate set of data.If you still have large excursions in AC RMS, maybe you have some popcorn noise or something.. Or EMC problem.

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 08:19:27 pm
content: Quote from: ebastler on November 06, 2023, 07:33:40 pm: 500 μV/div is a magnification of 1 mV/div setting. For vertical accuracy calculations, use full scale of 8 mV.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 08:34:11 pm
content: Quote from: ebastler on November 06, 2023, 07:33:40 pmI did it at 1us/div. because that's what Dave always does it at.Quote from: ebastler on November 06, 2023, 07:33:40 pmI was told that 1mV and 500uV were just software expansions of the 2mV range. I can't find it in the dtasheets though. I'm sure 2N3055 will fill us in on the details.

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 08:36:37 pm
content: Quote from: Fungus on November 06, 2023, 08:34:11 pmSee my post above. Copied from the datasheet. I'm too lazy to retype that much.: 500 μV/div is a magnification of 1 mV/div setting. For vertical accuracy calculations, use full scale of 8 mV.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 08:41:55 pm
content: Quote from: 2N3055 on November 06, 2023, 08:19:27 pmOk, it was the bottom two scales on the DHO900, only the bottom scale on the DHO800.I found it at the bottom of the datasheet:

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 08:42:19 pm
content: Quote from: Fungus on November 06, 2023, 08:34:11 pmIt was not meant to offend you.I just pointed out the facts. Even 1ms/div is kind of short really.. I would suggest doing it on longer timebases too. Just to see how much low frequency noise is there.As I said before, much as I like Dave, he makes mistakes too and is not always doing lots of preparations before doing videos.

author: ebastler
author_rank: Super Contributor
timestamp: November 06, 2023, 08:44:59 pm
content: Ok, so 1 mV/div is the highest "real" amplification. I think the DSO900 has an additional magnified step at the bottom end, 200 uV/div.If we assume that the scope does its noise calculations from the acquisition buffer (as opposed to the screen data like the DS1054Z), then using the magnified settings should neither improve nor falsify the results.

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 08:52:37 pm
content: Quote from: ebastler on November 06, 2023, 08:44:59 pmAll of the DHO scopes use same front end amp. They all have best 1mV/div. 200 and 500µV/div are software magnifications. 800/900 and 1000/4000...As as side not these are the covers I use. E-bay few bucks for a few of them..

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 09:07:12 pm
content: Quote from: 2N3055 on November 06, 2023, 08:52:37 pmHere's mine:

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 09:10:47 pm
content: The results are in...70Mhz full bw: 61.8uV100Mhz full bw: 64.2uV70MHz with 20Mhz limit: 56.38uV100MHz with 20Mhz limit: 56.83uVLet the arguments begin!

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 09:21:58 pm
content: This is all channels at 100MHz bandwidth. CH1 and CH2 have tinfoil, CH3 and CH4 don't.The winner is: CH3 - no tinfoil!I put a 50 Ohm terminator on CH3 and it went down to 38.8uV average.

author: Martin72
author_rank: Super Contributor
timestamp: November 06, 2023, 09:25:27 pm
content: Try average for acquisition...

author: ebastler
author_rank: Super Contributor
timestamp: November 06, 2023, 09:46:13 pm
content: Quote from: Fungus on November 06, 2023, 09:21:58 pmCould you also measure the residual offset voltage (V_avg) on each channel? It will enter the V_rms calculation and might have a non-negligible effect. Some of the traces do not look perfectly centered to their respective 0V arrows.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 09:49:06 pm
content: Quote from: Martin72 on November 06, 2023, 09:25:27 pmI set 32768 averages and it went down into the nV range. Rigol FTW!

author: Martin72
author_rank: Super Contributor
timestamp: November 06, 2023, 09:50:31 pm
content: @ebastler:All except channel 3, maybe he had forgotten to make a self-cal after his playaround with the bandwith down/upgrades.Btw, the title of the topic is somewhat irritating...Edit:QuoteNo wonder, given the number of passes selected.But then you also have to question the plausibility of the result.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 09:53:50 pm
content: Quote from: Martin72 on November 06, 2023, 09:50:31 pmYeah, I thought that, too. Does it change if somebody changes it?Edit: Apparently not. Maybe is has to be OP...

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 09:54:58 pm
content: Quote from: Fungus on November 06, 2023, 09:21:58 pmThese are nicely made measurements. Now AC RMS is stable and measurements look valid.Now people can compare to other scopes with same settings..FUN FACT: RMS measurements (AC+DC and DC only RMS) will work absolutely perfectly even with scope undersampling. They work by integrating (averaging) and if you just take enough samples it will converge to right result. It is valid technique used in many instruments.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 09:56:17 pm
content: Quote from: ebastler on November 06, 2023, 09:46:13 pmOh, yeah, I haven't done self-cal for a while. I have no idea what the bandwidth configuration was last time I did it.AC RMS shouldn't be affected by offset though.

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 09:58:20 pm
content: Quote from: Fungus on November 06, 2023, 09:49:06 pmWell it is logical...Noise is going to average to zero AC. What is left is DC offset..

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 10:00:03 pm
content: Quote from: Fungus on November 06, 2023, 09:56:17 pmAuto cal should compensate zero offset but also vertical gain..But these differences in channels are within normal spread. We are talking microvolts here...

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 10:01:34 pm
content: Quote from: 2N3055 on November 06, 2023, 09:58:20 pmIn AC RMS mode?

author: Martin72
author_rank: Super Contributor
timestamp: November 06, 2023, 10:03:47 pm
content: Watch the diagram in the vertical menu and think about again...

author: ebastler
author_rank: Super Contributor
timestamp: November 06, 2023, 10:16:10 pm
content: @Fungus -- a quick check for offset contributions in the non-averaged noise measurements is still relevant, I think. Either re-calibrate and do the V.rms measurements again, or measure V.avg in addition to V.rms and calculate V.noise = srqt (V.rms² - V.avg²).I would actually prefer the latter approach, which works even if the auto-calibration leaves some residual offset. As it does in my DS1054Z -- which comes in at approx. 400µV noise with the same 1ms/div, 1mV/div settings, by the way, in case anyone is still looking for a reason to upgrade.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 10:16:33 pm
content: One more before bed time...I did a self-cal and measured Vavg as well as AC-RMS. There's only 3 channels because that's all that fits in the visible area (you guys can't scroll tables up/down like I can):

author: Martin72
author_rank: Super Contributor
timestamp: November 06, 2023, 10:26:50 pm
content: These are pretty good values.One more thing about ac "mode" and dc-offset:When switching to ac coupling, a cap will be switched between signal input and the following stages in the frontend.This will have nearly no effect to the offset.AC coupling will block the dc offset of thesignal.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 10:28:12 pm
content: Quote from: Martin72 on November 06, 2023, 10:26:50 pm$399 Rigol FTW!

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 10:29:51 pm
content: Quote from: ebastler on November 06, 2023, 10:16:10 pmAC RMS (Stdev) excludes DC offset by definition. There is separate RMS measurement that is AC+DC RMS

author: ebastler
author_rank: Super Contributor
timestamp: November 06, 2023, 10:34:32 pm
content: Quote from: 2N3055 on November 06, 2023, 10:29:51 pmAh, thanks -- I had totally overlooked theAC.RMS bit.Just spent several minutes wondering how V.avg could possibly be larger than V.rms...I guess this means it's bedtime for me!

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 10:34:43 pm
content: Quote from: Fungus on November 06, 2023, 10:28:12 pmActually 100-120µV of offset is not so good as it could be . You should run self cal.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2023, 11:03:16 pm
content: Quote from: 2N3055 on November 06, 2023, 10:34:43 pmI just did!What was the spec of the vertical offset amplifiers again?I'm happy with 100uV.

author: 2N3055
author_rank: Super Contributor
timestamp: November 06, 2023, 11:09:06 pm
content: Quote from: Fungus on November 06, 2023, 11:03:16 pmIt is not bad. Just trying to see where is the baseline...

author: ebastler
author_rank: Super Contributor
timestamp: November 06, 2023, 11:10:09 pm
content: Quote from: Fungus on November 06, 2023, 11:03:16 pmI don't think Rigol specifies the allowable residual offset after self-cal. But it seems they know it's not perfect -- that's why the bias adjustment allows you to compensate for small offsets and drifts manually, right? (Section 5.10 of the manual.)

author: bdunham7
author_rank: Super Contributor
timestamp: November 07, 2023, 01:12:39 am
content: Quote from: 2N3055 on November 06, 2023, 09:54:58 pmHere you go:

author: Bob773
author_rank: Newbie
timestamp: November 07, 2023, 03:34:04 am
content: Thanks to all for the information regarding memory depth. BTW I changed the title since this took a bit of a turn… let me know if it needs changed again, I am here to please

author: Fungus
author_rank: Super Contributor
timestamp: November 07, 2023, 06:16:37 am
content: Quote from: bdunham7 on November 07, 2023, 01:12:39 amIs that a 1104X-E?Why is it worse with the bandwidth limit on?

author: tautech
author_rank: Super Contributor
timestamp: November 07, 2023, 06:26:41 am
content: Quote from: Fungus on November 07, 2023, 06:16:37 amOne of the X-E's.Only std dev on std dev is worse.Look at the Current value column.

author: iMo
author_rank: Super Contributor
timestamp: November 07, 2023, 08:28:07 am
content: On the above Siglent picture the aprox 80uVrms noise is aprox 500uVp-p seen on the screen which basically matches the theory. The standard deviation of 2.44uV is the STD for the set of measurements (the 51 measurements of that 80uVrms), not to mix it with the "rms".On the DHO804 picture the aprox 65uVrms is rather high, imho, that should lead to aprox 400uVp-p seen on the screen, so basically the "same level" as the Siglent.

author: ebastler
author_rank: Super Contributor
timestamp: November 07, 2023, 08:35:09 am
content: Quote from: iMo on November 07, 2023, 08:28:07 amItdoesget a bit confusing though, since the measured property isnotcalled "rms" here, but also "StdDev". So there is a measured StdDev, and it is measured with a certain StdDev. All correct, and the table layout does make it clear what's what; but it does invite mis-reading it at a quick glance.

author: iMo
author_rank: Super Contributor
timestamp: November 07, 2023, 08:46:32 am
content: Yep, there is AC.rms, AV+DC.rms, Vpp (or Vpk-pk), and STD.Btw., the noise levels of that Siglent and Rigol as depicted above are "almost the same" (20% diff in the noise is negligible). Thus the question is how the 8bit vs 12bit comparison would apply here..

author: 2N3055
author_rank: Super Contributor
timestamp: November 07, 2023, 09:33:41 am
content: Quote from: iMo on November 07, 2023, 08:46:32 amIt depends. Since SDS1104X-E has 500µV/div real range, for small signal it would be pretty much the same.SDS2000X+ shown above has much less noise than DHO800, despite being 8 bit. At 50Ω it would be even better (but so would DHO800 with external terminator).So like I said many times before, it is not that simple.All in all, Rigol finally made an inexpensive scope with quite competitive noise levels. It is not as good as good 12 bit scopes, and not even as good as best 8bit ones, but good nevertheless. Noise is no longer a problem. Especially for the price bracket.It would be interesting to see how well DHO4000 fares.

author: Serg65536
author_rank: Regular Contributor
timestamp: November 07, 2023, 10:29:34 am
content: Quote from: Fungus on November 06, 2023, 09:56:17 pmPlease, share your experience:1) What is the DC accuracy of your DHO804 scope with DHO924 firmware?The good way to measure it is to test some precisely known voltage around 8V on 100mV/div range with offset.2) You use vendor.bin upgrade or whole 924 firmware image?My 804 has worst accuracy of 1.6% with 924 firmware image, when zero offset is calibrated.

author: ebastler
author_rank: Super Contributor
timestamp: November 07, 2023, 11:38:55 am
content: Quote from: iMo on November 07, 2023, 08:46:32 amI would expect that at the very low end of the range (high amplification), noise levels are dominated by the analog front end. ADC resolution comes into play when you look at the dynamic range. So an 8-bit scope with a carefully designed front end can fare pretty well in this test.The Siglent SDS2000X plus in 10-bit mode has the lowest RMS noise in the measurements above. That makes sense to me, since the oversampling & averaging it performs in that mode should also help to reduce the (digitized) front-end noise.

author: rf-loop
author_rank: Super Contributor
timestamp: November 07, 2023, 12:48:09 pm
content: Quote from: Fungus on November 06, 2023, 10:16:33 pmNot bad at all.For compare.Here Siglent low end model. (1204XHD China only model).Same 1ms/div and 10k Mem but in Siglent it have 1MSa/s instead of 500kSa/s as in Rigol in your image (because Rigol want display here only half length of acquisition and hide other half. Then other half is possible to look only after stop acquisition. Maybe it's exciting when everything isn't shown and revealed right away. I think that kind of thing would be better suited for a bedroom than to a measuring device. But let everyone do it in their own way.)Note here is used 4 channels what all have different setup. 20MHz limit/100MHz limit, 1Mohm input and 50ohm input.(100MHz limit is forced by system when more than 2 channels simultaneously in use - because real ADC samplerate!)

author: ifonlyeverything
author_rank: Regular Contributor
timestamp: November 07, 2023, 01:16:48 pm
content: Is a hacked DHO800 an upgrade from a Siglent SDS1104X-E? I'm interested in the HDMI output + smaller form factor (small workspace) unless it's a bad trade-off in some way or another.

author: ebastler
author_rank: Super Contributor
timestamp: November 07, 2023, 01:56:23 pm
content: Quote from: ifonlyeverything on November 07, 2023, 01:16:48 pmThat depends a lot on which functionality is important to you. Here's my take:Clear advantages of the DHO800:- Smaller form factor, USB-C supply (if powerbank operation is of interest).- Nicely implemented touch interface (plus classical controls and the dual multi-function knobs).- 12 bit resolution -- not so much for lowest-level noise, but dynamic range, e.g. in FFT.Clear advantages of the Siglent (if relevant to you):- Logic analyzer upgrade possible -- although via somewhat expensive external unit with some limitations.- Bode plots, if you have an external Siglent function generator.Both functions would require you to get a DHO9xx or DHO9xxS if you want them in the Rigol series.Philosophical/debatable differences:- The scopes differ in various details, regarding their trigger, protocol decoding and measurement options. No clear winner here in my opinion, but it's worth checking the datasheets if some particular functionality is important to you.- UI design is a matter of taste, I'd say. Siglent fans will argue that the restrained and space-saving design of the Siglent UI is more functional and professional; Rigol fans will argue that the Siglent layout and fonts look a bit old-fashioned and that they find it easier to get their bearings with Rigol's visual cues. Look at a few still pictures and/or Youtube videos to see whether you have a strong personal preference there.

author: bdunham7
author_rank: Super Contributor
timestamp: November 07, 2023, 02:59:19 pm
content: Quote from: Fungus on November 07, 2023, 06:16:37 amIt says "1104X-E" on the front but it thinks it is a 1204X-E, 200MHz BW.The noise is lower at 20MHz BW, as I think has been explained.

author: tautech
author_rank: Super Contributor
timestamp: November 07, 2023, 07:36:27 pm
content: Quote from: ifonlyeverything on November 07, 2023, 01:16:48 pmYou may need to consider a bigger picture.Do you have a PC on/near the bench as the webserver provides for porting to a large display.X-E sampling rates and mem depth are superior with all channels active unless the 800 is hacked which only provides greater mem depth.BTW, did you know all X-E models have been reduced in price.

author: Martin72
author_rank: Super Contributor
timestamp: November 07, 2023, 08:01:33 pm
content: This is not the right thread for this, but...QuoteEveryone hacks their scope...You can expand the memory to 50Mpts and increase the bandwidth to 200Mhz(DHO804).The display is higher resolution and touch, you can get several windows with signals on the screen and it has 12 bit as normal resolution instead of 8bit + 3bit Eres (which costs bandwidth).You can connect a larger screen via hdmi and therefore do not have the problem of having to establish a network connection.The Rigol also has a web server on top.

author: ebastler
author_rank: Super Contributor
timestamp: November 07, 2023, 08:09:04 pm
content: Quote from: tautech on November 07, 2023, 07:36:27 pmNo need to sell him an 1104X-E, he already has one!But I would agree that switching from that to a DHO800 only makes sense if one is explicity interested in the "package" features of the DHO: Small form factor, VESA mount, HDMI out, USB-C supply (with power bank option). And it does imply some compromises, e.g. on the sampling rate when used in 4-channel mode.On the other hand, if HDMI is of particular interest: I would not count the X-E's web server as a replacement for the DHO's HDMI out, especially compared to using an external touch screen on the DHO. While the web interface seems quite responsive, it can't offer the same user experience, by design, since the X-E is not a touch-screen scope.

author: Fungus
author_rank: Super Contributor
timestamp: November 08, 2023, 06:28:51 am
content: Quote from: ebastler on November 07, 2023, 08:09:04 pmQuote from: tautech on November 07, 2023, 07:36:27 pmI wonder why...?

author: Fungus
author_rank: Super Contributor
timestamp: November 08, 2023, 06:47:30 am
content: Quote from: bdunham7 on November 07, 2023, 02:59:19 pmYeah, I know that...I think I'm confused about which channel has the bandwidth limited. I thought it was the cyan channel but it might be the yellow channel.Does this little 'B' indicate the bandwidth limiter?

author: ebastler
author_rank: Super Contributor
timestamp: November 08, 2023, 06:53:00 am
content: Quote from: Fungus on November 08, 2023, 06:47:30 amYes, that's the indicator you want to look at. I also got confused at first glance by the "BW Limit 20M" at the bottom of the screen. (In a blue color which looks pretty much the same as the cyan channel to slightly colour-blind me.)

author: tautech
author_rank: Super Contributor
timestamp: November 08, 2023, 07:04:01 am
content: CH1 in white letters indicates which channel menu is selected.

author: Fungus
author_rank: Super Contributor
timestamp: November 08, 2023, 07:35:44 am
content: Quote from: ebastler on November 08, 2023, 06:53:00 amYep, that's what fooled me, too.

author: Fungus
author_rank: Super Contributor
timestamp: November 08, 2023, 07:40:35 am
content: Quote from: tautech on November 08, 2023, 07:04:01 amThis?I'm definitely going with "Rigol wins" on that one...And to the guy who's asking if the Rigol would be an upgrade to his SDS1104X-E: This kinda sums it up for me. Look at the difference in the indicators, fonts, etc. The Rigol is justnewer, and feels like it when you're using it.The overall abilities are very similar but which would you rather own?

author: rf-loop
author_rank: Super Contributor
timestamp: November 08, 2023, 07:54:42 am
content: Quote from: bdunham7 on November 07, 2023, 01:12:39 amExcept that @Fungus have used 500kSa/s and 10k acquisition length. Your images visible traces have up to 4000 times more data...(and data visible only 5k. Least I do not know if Rigol use only visible part of acquisition data for measurements or whole total acquisition length but this is not an important thing in this case. Let's hope some also test this thing using some suitable test signal.)

author: Fungus
author_rank: Super Contributor
timestamp: November 08, 2023, 08:00:52 am
content: Quote from: rf-loop on November 08, 2023, 07:54:42 amNope, this is the image being referred to by 2N3055 :I don't think it will make any difference for RMS though.

author: tautech
author_rank: Super Contributor
timestamp: November 08, 2023, 08:49:02 am
content: Quote from: Fungus on November 08, 2023, 07:40:35 amYes, the channel menu indicator which matches the channel tab info you conveniently deleted.

author: rf-loop
author_rank: Super Contributor
timestamp: November 08, 2023, 08:55:14 am
content: Quote from: Fungus on November 08, 2023, 08:00:52 amOf course. All this is explained in old Agilent paper what all know.Evaluating Oscilloscope Vertical Noise Characteristics, Application Note 1558With this kind of random noise trace visual fatness rise some amount when displayed data density rise (because noise is random and with more data we get more probability to catch more highest peak values..But this leads to one thing.If we use very very different amount of data... as in my previous message I told your one image have 5k data on display and other peoples (@bdunham7) image with other oscilloscope have 4000 times and 2800 times more data on display what produce more "fat" trace and many peoples may only fast look images and mind may produce imagination about noise level from trace fatness instead of measured numbers. We all know how peoples mind produce imaginations.So as far as possible I recommend to use around same settings (this msg was not based to you (and your other image) but as you see other people use image where was just after your 10k/500kSa image his ( @bdunham7 ) images where was used 2GSa 20M and 14Mpts. And my comment was just for this case.

author: Fungus
author_rank: Super Contributor
timestamp: November 08, 2023, 09:08:41 am
content: Quote from: tautech on November 08, 2023, 08:49:02 amI deleted them because I couldn't seeanyindication there that one of them was highlighted or related to the the bottom menu.Is there anything else on screen to indicate which channel is selected apart from the white "CH1"?

author: tautech
author_rank: Super Contributor
timestamp: November 08, 2023, 09:35:45 am
content: Quote from: Fungus on November 08, 2023, 09:08:41 amYes, the active to the controls and selected channel trace is always atop all other channels.The channel button is illuminated and that channel menu is shown unless you use the Hide Menu feature.

author: Fungus
author_rank: Super Contributor
timestamp: November 08, 2023, 09:47:46 am
content: Quote from: tautech on November 08, 2023, 09:35:45 amSo... Rigol has a much shallower learning curve.Got it!

author: tautech
author_rank: Super Contributor
timestamp: November 08, 2023, 09:58:19 am
content: Quote from: Fungus on November 08, 2023, 09:47:46 amYep, no probe attenuation info.

author: Fungus
author_rank: Super Contributor
timestamp: November 08, 2023, 03:38:43 pm
content: Quote from: tautech on November 08, 2023, 09:58:19 amYeah.... that'sSOmuch more important than knowing which trace is going to move or change scale when you twist a knob.All the channel settings are only a gesture away.

author: bdunham7
author_rank: Super Contributor
timestamp: November 08, 2023, 04:06:37 pm
content: Quote from: rf-loop on November 08, 2023, 08:55:14 amFor those of you faked out by the blue menu colors, in real life Siglent is using a blue color for active menu items, including the selected channel parameter, the "Trig'd" indicator, the trigger point and so forth. This is quite distinct in real life from the cyan channel color, although that may not be obvious on your monitor or if you have color-blindness. Unfortunately there's no option to change the colors.I missed the fact that the memory and sample rate were much reduced in the other examples. Why was that done anyway? In any case, here is the SDS1204X-E at 1MSa/s and 14kpts. Also, I added another screenshot showing how much of the noise in the Siglent is low-frequency. In addition, it might be good to compare scopes at 1V/div as well, to see how much of the fat traces are due to front-end noise at the lowest levels and how much is due to other factors. Some scopes don't quiet down proportionally as you decrease the gain and still have fat traces at the higher V/div settings. At 1mV/div, it looks like both the Rigol and the Siglent (1204X-E) have an ENOB of just under 7. I'd hope to see the Rigol doing much better at 1V/div.

author: Fungus
author_rank: Super Contributor
timestamp: November 09, 2023, 11:09:12 am
content: Quote from: bdunham7 on November 08, 2023, 04:06:37 pmYeah, it's obvious (sorta) when youknowit... but it wasn't obvious to a few people just by looking at a screenshot.Hence my comment about "learning curve".

author: bdunham7
author_rank: Super Contributor
timestamp: November 12, 2023, 08:25:41 pm
content: Quote from: Fungus on November 09, 2023, 11:09:12 amIt's obvious enough when you're actually using the scope, so the only learning curve would be for reading screenshots. And Siglent seems to be good about getting most of the necessary information to interpret a signal up on the screen.Can you try what I suggested and post a screenshot of your scope at 20MHz and Full BW, 1ms/div, open connectors but at 1V/div? I'm curious what you'd get for ENOB when you get out of the lowest scales.

author: ebastler
author_rank: Super Contributor
timestamp: November 12, 2023, 09:08:47 pm
content: That would be a tad more than 11 bits of effective resolution, right? Assuming 9 vertical divisions (with a bit of margin at the top and bottom), it's 9*50 mv / 0.2 mV = 2250 > 2048.

author: Fungus
author_rank: Super Contributor
timestamp: November 12, 2023, 09:13:47 pm
content: Quote from: bdunham7 on November 12, 2023, 08:25:41 pmSecond attempt, with the right vertical scale:CH1+CH2 @20MHz, CH3+CH4 full.

author: ebastler
author_rank: Super Contributor
timestamp: November 12, 2023, 09:18:00 pm
content: Hmm -- pity that you deleted the screenshots taken at 50 mV/div. Those actually had a higher ENOB (yes, I know that's not quite it...) than at 1 V/div.For the 1 V/div acquisitions, I get 9*1000 mV / 5 mV = 1800, so a bitlessthan 11 bits.

author: Fungus
author_rank: Super Contributor
timestamp: November 12, 2023, 09:21:29 pm
content: Quote from: ebastler on November 12, 2023, 09:18:00 pmI can do them again:

author: bdunham7
author_rank: Super Contributor
timestamp: November 12, 2023, 09:30:36 pm
content: Quote from: ebastler on November 12, 2023, 09:18:00 pm9? But yeah, I'm seeing 10+ ENOB, pretty good actually.

author: ebastler
author_rank: Super Contributor
timestamp: November 12, 2023, 09:33:20 pm
content: Quote from: bdunham7 on November 12, 2023, 09:30:36 pmI don't have the DHO800 myself, but was assuming that the full ADC range is not mapped to exactly 8 vertical divisions, but that there is approx. half a division of "margin" at the top and bottom.Edit: Dave shows it here for the MSO4000.

author: bdunham7
author_rank: Super Contributor
timestamp: November 12, 2023, 09:33:56 pm
content: So here is the SDS1204X-E, the second one is expanded after capture to show that there's essentially 1LSB of flipping, so the noise probably can't get any better. But I get an ENOB ofa bit more than 8 bits--8.977.5 based only on noise? IOW, this is as far as 8-bit tech can go here and the DHO800 clearly exceeds that at these scales.

author: Martin72
author_rank: Super Contributor
timestamp: November 12, 2023, 09:34:36 pm
content: Determining the ENOBs ( at 10Mhz) of a DHO4000 and R&SMX04:https://electronicprojectsforfun.wordpress.com/to-enob-or-not-to-enob/

author: gf
author_rank: Super Contributor
timestamp: November 12, 2023, 09:39:38 pm
content: Quote from: ebastler on November 12, 2023, 09:18:00 pmQuote from: bdunham7 on November 12, 2023, 09:30:36 pmBut 9Vpp(provided that is the full scale range of the ADC) is only 3.182VRMS, for a full scale sine wave. Then the SNR is 20*log10(3.182/0.005) = 56.075 dBFS, or equivalently (56.075-1.76)/6.02 = 9.0224 ENOB.

author: bdunham7
author_rank: Super Contributor
timestamp: November 12, 2023, 09:41:31 pm
content: Quote from: gf on November 12, 2023, 09:39:38 pmDoh! I knew I had some error in there somewhere.

author: ebastler
author_rank: Super Contributor
timestamp: November 12, 2023, 09:55:03 pm
content: Quote from: bdunham7 on November 12, 2023, 09:41:31 pmSame here... Thanks!

author: Fungus
author_rank: Super Contributor
timestamp: November 13, 2023, 02:07:48 am
content: Quote from: ebastler on November 12, 2023, 09:33:20 pmI can grab a 2Vpp signal in the 200mV/div range. That means it has a whole division above/below the screen.Quote from: bdunham7 on November 12, 2023, 09:30:36 pmThis one goes to 10!

author: Fungus
author_rank: Super Contributor
timestamp: November 13, 2023, 02:17:23 am
content: Quote from: gf on November 12, 2023, 09:39:38 pmOn the 1V range: 20*log10(3.535/0.005) = 56.998dB = 9.17 ENOBQuote from: ebastler on November 12, 2023, 09:18:00 pmOn the 50mV range I get ... 64.95dB = 10.5 ENOB

author: 2N3055
author_rank: Super Contributor
timestamp: November 13, 2023, 07:38:45 am
content: Quote from: Fungus on November 13, 2023, 02:17:23 amMartin posted a link to article about ENOB measurements. It seems not all read it, but here we are, magic numbers are coming out of the hat.Measuring ENOB in scopes is made in accordance to IEEE Std 1057™ standard "IEEE Standard for Digitizing Waveform Recorders".There are many nice articles by various scope manufacturers on the topic.ENOB is calculated from SINAD (Signal to noise and distortion) ratio. It is measured by inputting low distortion sinewave (better than scope measured) and sweeping across a frequency BW of scope. ENOB is measured as a curve, a graph, not a single number.It will vary with with frequency.On scopes it is measured with signal that is 90% of full screen.In this case it would be 7.2V P-P for DHO800 1V/div.That curve than gets statistics treatment and some kind of average or worst case scenario number is picked by marketing. Siglent publishes worst case scenario ENOB number with some reserve included, for instance, making it very conservative number. They guarantee it will be better than number published. It is always better than that. Most manufacturers are the same in that regard. Rarely manufacturers (any of them) publish full characterisation of ENOB curves directly in datasheet.It is definitelynota ratio of scope AC RMS measurement of noise floor and theoretical RANGE of ADC.Since really measuring ENOB is out of reach of many (no wide BW signal source of sufficient quality) we can compare and talk about just noise floor levels VS full screen scale. Which is definitely not the same as ENOB.In which case it is simply SNR (signal to noise ratio). Expressed in dB.We could talk about bits equivalent of SNR but that is not usually made because it has no practical meaning.But this is not ENOB. ENOB needs signal applied and includes distortions (nonlinearities, sampling jitter...) . It is already a simplified metrics....One another note: DHO800 has 8v P-P range on screen. That equates to 2,8369 V RMS sinewave.That is your usable full dynamic range. The rest is reserve to prevent clipping.

author: Fungus
author_rank: Super Contributor
timestamp: November 13, 2023, 09:14:05 am
content: Quote from: 2N3055 on November 13, 2023, 07:38:45 amThat's when you're measuring THD, which we aren't. If you're measuring noise you should use the full range of the ADC for most accurate results.Quote from: 2N3055 on November 13, 2023, 07:38:45 amhttps://en.wikipedia.org/wiki/Effective_number_of_bitsThe SNR tells you the ENOB when distortion is zero.As noted: Calculating THD requires a lot of fancy gear that most people simply don't have.OTOH it's a safe bet that THD is small, almost negligible. SNRwillgive a good approximation. It's the best number we have until more data comes along.It's also a safe bet that using the same method on different 'scopes is a good way to compare them. We measured the "benchmark" Siglent using the same yardstick and found the new Rigol has two or three more bits more.I think that's a fair assumption to make.ie. Rigol's 12 bits are a big advance and this little 'scope has proved itself to be the new reference point.

author: ebastler
author_rank: Super Contributor
timestamp: November 13, 2023, 09:44:02 am
content: Quote from: 2N3055 on November 13, 2023, 07:38:45 amYes, I know. That's why I initially talked about "effective resolution", and then added a disclaimer ("I know that's not quite it") when I mentioned ENOB later. Using the full ADC range was obvioulsy a brain fart, but when using full RMS signal amplitude instead -- how big is the difference between proper ENOB and that simplified "RMS full swing / RMS noise" in practice?QuoteNot sure I agree on this. The oscilloscope has the larger range captured, as witnessed by the ability to zoom out (vertically) on the stored data. You can also use the full range when you want to zoom in on small signal details which sit on top of a large signal swing. And I am pretty sure that the extended vertical range can also be used for measurements.

author: gf
author_rank: Super Contributor
timestamp: November 13, 2023, 09:55:11 am
content: Quote from: 2N3055 on November 13, 2023, 07:38:45 amYes, actually it should be calculated from SINAD, and it is a function of frequency.Calculating it from SNR is just a first order approximation, assuming distortion is low.At low frequencies it is not unlikely that this is granted, but at high frequencies I would not be so sure.EDIT: DC non-linearity could also be measured during factor calibration, and compensated. But of course I don't know if the manufacturer does that.

author: 2N3055
author_rank: Super Contributor
timestamp: November 13, 2023, 10:22:19 am
content: Quote from: Fungus on November 13, 2023, 09:14:05 amYes we all know you are smarter than IEEE combined...SNR tells you what is SNR. Without signal. There is no "zero distortion" in real life. Why do you think ADCs with nominal 12 bit resolution barely break 10bit ENOB?Nonlinearities. So no it is not negligible and no it is not even close to good approximation. Take a look at IEEE Std 1057™. It is 181 pages or so...We measure and calculate. As I said there are excellent white papers by R&S, Keysight and Tek on the topic. Also few good ones on EDN.No fancy anything needed for that. Just will to read and learn."An encyclopedia (American English) or encyclopædia (British English) is a reference work or compendium providing summaries of knowledge either general or specialto a particular field or discipline" . Quote from Wikipedia itself.Wikipedia is encyclopedia. It is just a summary to explain what word means. And to point you in the right direction where can knowledge of the topic be found. It is simply the index to give you starting point on a path to knowledge. It is not THE knowledge.Fact that you cannot measure it means exactly that. YOUcannotmeasure it. Live with it. You have no clue what ENOB is on DHO800 and you never will unless either you acquire capability to measure it, or someone measure it for you. Stop inventing fantasy numbers. If you want to gamble go to bookies..Comparing SNR is not wrong. I sad that. But you keep inventing "your special" ways of doing it. To be able to compare you need to compare at same conditions.I told you how: full screen is considered full range. By Tektronix, Keysight LeCroy, Siglent ... For your scope that is 8 div vertical. 8 V P-PAt 1 V/div and full BW your scope has cca 55dB od SNR. At 20 MHz BW about 56-57 dB.55dB at almost 200MHz BW is not bad. Not bad at all.

author: 2N3055
author_rank: Super Contributor
timestamp: November 13, 2023, 10:28:07 am
content: Quote from: gf on November 13, 2023, 09:55:11 amYes, as I said we can compare SNR as it is a simple measurement and can be done in consistent manner and give good insight in large part of performance envelope.If scope SNR is bad , ENOB won't be better.As a rough estimate, if two scopes have same ranges and similar BW simply putting them in same range makes simple noise AC RMS comparisons meaningful.If scope has 10 vertical divisions and another one has 8 at 1V/div they won't be the same but simple linear scaling works here.Some scopes have nonlinearity compensation as a part of ADC calibration of masivelly interleaved ADCs (Keysight for instance. Maybe Rigol does something similar.in its ASIC ADC) Some have digital compensation after ADC, but not in this price range.

author: 2N3055
author_rank: Super Contributor
timestamp: November 13, 2023, 10:44:20 am
content: Quote from: ebastler on November 13, 2023, 09:44:02 amIn practice difference will be exactly based on how much distortion is there. Make note that whole spectra of distortion artefacts from full BW will add up to RMS of baseline. Death by thousands cuts type of scenario.As for vertical range used for calculation, I said what is industry practice. It stems from the fact that scope screen is visual reference and part that manufacturer guarantees specifications for. Not my invention.By all means, if you use scope as sampler, and pull data somewhere else and postprocess, characterize it fully for full usable dynamic range (by characterizing distortion and clipping behaviour) and enjoy.But on a scope you are left at mercy of manufacturer provided usage envelope.Small part of dynamic range is reserve not mapped in normal use for user.It is same for everyone. It is still fair if you compare like for like..

author: Martin72
author_rank: Super Contributor
timestamp: November 13, 2023, 10:55:59 pm
content: At the moment I am working on the ENOB measurement from the linked page as a kind of side project.I have already finished the 10Mhz oscillator and successfully put it into operation, I have summarized the filters used for it and designed 2 circuit boards for it, I will soon know if this works.And open a new thread for it, the test object will of course be my HD from siglent - but I also have the DHO804.The website operator is a user from here, he has measured a DHO4000 there and an MX04.At first I was amazed that he came up with such "high" results, over 10 bits after all.Rigol had simply stated "over 8bit" in the data sheet, siglent is a bit more precise and declares values between 8.4 and 8.7.When I later looked into the ENOB thing, it was clear why.And therefore it is also clear why this thread comes to just under 11bit, because the frequency is left out or is much lower(10Mhz) than used by the manufacturers.Very professional, by the way:Rigol simply states "over 8 bit" and conceals the measuring circumstances.Siglent also states the underlying frequency (50 or 100Mhz) in addition to the more precise values.It was clear to me that ENOB depends on the frequency, among other things.More on this soon, probably towards the end of the year when I don't have to work.

author: gf
author_rank: Super Contributor
timestamp: November 14, 2023, 08:40:02 am
content: Quote from: Martin72 on November 12, 2023, 09:34:36 pmLet me supplement this with a fairly comprehensive application note from LeCroy:https://cdn.teledynelecroy.com/files/appnotes/computation_of_effective_no_bits.pdf

author: gf
author_rank: Super Contributor
timestamp: November 14, 2023, 03:55:48 pm
content: Quote from: Martin72 on November 13, 2023, 10:55:59 pmIf the aim is to measure only at a single frequency, then I wonder, why not use a high-Q bandpass filter?Google found for me e.g. these crystal filters:https://www.amazon.de/Kristallfilter-Schmalbandfilter-Langlebig-spezielle-Instrumente/dp/B09MJP1Y14They seems to be available from various sellers, and also for a couple of different frequencies, e.g. herehttps://de.aliexpress.com/item/1005003627277580.htmlThey promise > 80dB stopband attenuation, and if they deliver what they promise, this should be more than enough for measuring a 12-bit ADC (-74dBFSquantization noise), in conjunction with an AWG like SDG2000X which achieves already -65dB harmonic distortion up to 10MHz and -70dB non-harmonic spurs out of the box (according to the datasheet).

author: Martin72
author_rank: Super Contributor
timestamp: November 14, 2023, 10:50:50 pm
content: Interesting comments, but I would like to take them up in a separate thread.That would go beyond the scope of this article.

author: JDW
author_rank: Frequent Contributor
timestamp: January 17, 2024, 04:25:57 am
content: Quote from: Fungus on November 12, 2023, 09:21:29 pmWhen I try to repeat the same test using the same settings, even when testing only a single channel (leaving the probe disconnected as Fungus apparently did), I get 60Hz noise that makes it impossible to detect the true noise floor. Noise remained unchanged with or without the ground cable attached to wall socket Earth Ground.Note that my Probe switch was set to 10x, and the "Probe" setting (in CH1) was also set to 10x.

author: ebastler
author_rank: Super Contributor
timestamp: January 17, 2024, 08:20:27 am
content: Quote from: JDW on January 17, 2024, 04:25:57 amBut your probe isnotdisconnected! Your photo shows that it is connected to the scope, and its tip is left "floating", not connected to any defined potential. It is normal that the probe essentially acts as an antenna then, picking up all kinds of noise from the environment.I don't know how Fungus had configured the inputs for his earlier measurements, but it am pretty sure it was not the configuration you show:When people refer to "open inputs", they mean that nothing at all is connected to the scope's BNC jack.To really measure the internal noise of the scope, the inputs should be shorted directly at the BNC jack, or a 50 Ohm termination installed there.If you want to measure the background you can expext in a "real world" scenario, you can connect the probe to the scope, and then connect the probe's little ground strap to the tip. Even that little loop can pick up magnetic fields from the environment; we had reports from one user who could receive nearby FM radio stations that way.

author: JDW
author_rank: Frequent Contributor
timestamp: January 17, 2024, 08:50:37 am
content: Quote from: ebastler on January 17, 2024, 08:20:27 amThank you for explaining. I choose to be more clear in my own personal wording in that if I mean for somebody not to connect any probe at all, I will tell them "no probe attached." That's 100% clear, with zero guesswork for veterans or newbies alike. Words like "disconnected" can mean multiple different things. Even "open input" isn't necessarily clear if you've not learned the meaning. "No probe attached" is just that.I don't have a 50Ω terminator, and I am basically trying to replicate what Fungus did because that is established data we can go by. No, his work is not a gold standard, but it is a nice frame of reference that other people can try to see if we get the same thing.Currently, my scope's "Probe" settings for each channel are set to10x, and that's because I normally use my Probes mechanically switched to the 10x setting. But we're doing this particular test with "no probe attached" so...When displaying only CH1 and with CH1 set to Probe:10X: The "Current" column shows about600uV(Fungus was about 200uV)When displaying only CH1 and with CH1 set to Probe:1X: The "Current" column shows about60uV(Fungus was about 200uV)I assume Fungus must have used 1x or 10x, so in either of those cases, my numbers are not close to his.When I attach my probe to CH1 and mechanically set its switch to 10x, then set the scope's CH1 setting to Probe: 10x too, and then connect the probe's GND to the probe's tip (as per your bullet point 3): The "Current" column shows about476uV(Fungus was about 200uV) But you will likely explain that as being a matter of the ground strap picking up noise and radio stations.I then tried your bullet point #2, shorting the inner gold pin of the CH1 BNC to its ground using the shortest wire possible. I get a "Current" column value of256uV, which is higher than the values Fungus showed, but we don't know exactly how he measured either. Even so, it least this test was in the ballpark of his. So I am largely satisfied with that result.Thank you for your kind assistance.

author: 2N3055
author_rank: Super Contributor
timestamp: January 17, 2024, 09:15:25 am
content: It depends on what are you measuring.Putting a 50Ω on 1MΩ input "simulates" what noise would be if input were 50 Ω.Putting a shielding cover over BNC better "simulates" noise at 1MΩ input impedance.Setting probe ratio to 1:1 will measure "native" noise.Setting probe to 10x (which is really 1/10 but that is another story) will measure probe tip referred noise, i.e. what is your baseline noise floor when using 10x probe.A probe "simulator" could be made, with low noise 9 MΩ resistor to ground, in a nice shielded box, connected to input BNC directly. That would simulate connected probe with grounded tip, with no interference. WIth scope set to 10x it would best simulate what a baseline nose would be at 1 MΩ with the ideal 10x probe.Like I said before, just measuring something without establishing clear protocols and rules ends up with bunch of measurements that means very little because they cannot be directly compared and have no correlation any real world scenario.And unlike BW measurements that need expensive and calibrated signal generators, some things require little investment, but some rigor and attention and some set rules.

author: ebastler
author_rank: Super Contributor
timestamp: January 17, 2024, 09:41:15 am
content: Quote from: JDW on January 17, 2024, 08:50:37 amWhen you are interested in the noise generated internally in the scope, you should always use 1x as the probe setting. In the 10x setting the scope will "assume" that the signal it sees has been divided by 10 by an external probe. So e.g. 60 µV of noise from its internal input amplifiers will be reported as 600 µV, which is misleading.If you don't have a termination resistor handy, leaving the BNC input unconnected but shielded is probably the most meaningful test you can do. As 2N3055 explained, that will give you the noise generated by the scope's input section when set to 1 MOhm (i.e. ready for an external probe), but without the "antenna" contributions from an actual probe. You can try and make some improvised shielding from copper or aluminim foil around the BNC jack.When comparing noise figures, you will also notice that they depend on the scope's time base setting and sampling rate. Going to slower time bases lets the scope capture the low-frequency components of the noise -- which are significant, since there are noise cmponents where the amplitude follows a 1/f curve. Increasing the sampling rate (by increasing the memory depth used, in the Acquisition menu) lets the scope capture higher-frequency contributions, which also add more noise. So when comparing to measurements made by others, be sure to use the same acquisition settings.

author: Aldo22
author_rank: Super Contributor
timestamp: January 17, 2024, 11:06:49 am
content: Interesting topic (noise measurement).I only have a Hantek at the moment, but the problem will probably remain the same.Without a checklist, you always forget a setting.- Acquisition Mode: Normal - Average - Peak - HR give different results.- 20MHz bandwidth limitation- Probe attenuation settings- V/div and s/div- Input coupling GND- With the Hantek, the sampling rate also makes a difference.Have I forgotten something?All these settings give me different noise values. Is it the same with the Rigol?The "calibration kit" (Open, Short, Load) of the NanoVNA is quite handy for testing with a BNC-SMA adapter (Attachment) ...and cheap..

author: Fungus
author_rank: Super Contributor
timestamp: January 17, 2024, 08:09:46 pm
content: Quote from: JDW on January 17, 2024, 08:50:37 amJust don't connect anything to it. Bare BNCs. 50Ω terminator isn't necessary.I tried covering them with tin foil to prevent radio interference but it made no difference here.YMMV, it depends where you live and what's around you.Quote from: JDW on January 17, 2024, 08:50:37 amGee, thanks...Quote from: JDW on January 17, 2024, 08:50:37 amThe ONLY thing probe 10x setting does is divide all the numbers shown on screen by 10 because the probe has a 10x resistor divider inside it. It makesnochanges to the hardware.The setting should obviously be at 1x to show correct values for this test.

author: Bud
author_rank: Super Contributor
timestamp: January 17, 2024, 09:48:16 pm
content: Quote from: Aldo22 on January 17, 2024, 11:06:49 amYes. A cookie tin box large enough for the scope to fit inside, strapped with a gage 8 wire to the cold water pipe.

author: JDW
author_rank: Frequent Contributor
timestamp: January 17, 2024, 10:08:45 pm
content: Quote from: Fungus on January 17, 2024, 08:09:46 pmReally?? 1x?As mentioned in the closing sentence of my previous post, I get a "Current" column value of256uVwhen the scope is set to10x. Changing the scope setting for CH1, which is the channel I was testing) to1xwould then show a value of25.6uV. Your measured values were approximately200uV. Therefore, I do believe the 10x setting on the scope must be correct unless one wishes to argue that a measured value of 25.6uV is correct, which would then means my scope is significantly lower noise than yours.Note that in that final test, I had no probes attached. I merely shorted the middle BNC pin to its outer ground via the shortest wire possible.

author: Bud
author_rank: Super Contributor
timestamp: January 17, 2024, 10:14:36 pm
content: Quote from: JDW on January 17, 2024, 10:08:45 pmNo "would". Switch and check. You were advised to do the right thing.

author: JDW
author_rank: Frequent Contributor
timestamp: January 18, 2024, 01:30:37 am
content: Quote from: Bud on January 17, 2024, 10:14:36 pmBased on your strongly worded remarks above, I suspect that if I had said"When you wet your fingers and then short them across bare wires in your wall socket with active AC power flowing, you would receive a shock"you would have told me: "try it and see."Here's the video proof you asked for, which again, is only common sense and is but an extension of the same testing I did yesterday...https://youtu.be/OEXGotlZeiIFor those too lazy to watch the video evidence, the fact is that the numbers shown in the "Current" column are 10x larger when you set your channel to 10x (scope setting) as compared to the numbers in the "Current" column when you set the scope to 1x, for the particular channel being used at the time, which in my case is CH1. This is exactly what I said previously.Now I hope that settles it.

author: Aldo22
author_rank: Super Contributor
timestamp: January 18, 2024, 12:17:52 pm
content: Quote from: Bud on January 17, 2024, 09:48:16 pmTo shield the lab from the noise of the oscilloscope or the other way around?

author: ebastler
author_rank: Super Contributor
timestamp: January 18, 2024, 06:31:32 pm
content: Quote from: JDW on January 18, 2024, 01:30:37 amThat's just Bud. He is very much into short and strongly worded remarks.