New scope Siglent SDS1000-E, newbie question - Page 1
Forum section: electronics / testgear

author: Agosto
author_rank: Contributor
timestamp: January 06, 2022, 09:22:12 pm
content: Hi,I am new to the digital scope world. Have much experience with analog (tube) scopes though. Just bought a new scope Siglent SDS1000-E and have the following problem/question:Whenever I display signals, the signals are overlayed with some high frequency distortion. See Photo. Aside from making the read-out more difficult, it also has an influence on the trigger function which causes the image to jump horizontally. I am using the probes supplied with the scope. I also used another (old) test probe from my analog scope. I understand that the scope has some HF filters and I applied them. When doing so the image stabilizes but the image is still distorted. The smaller and more complex the signal (e.g. music), the more prevalent is the distortion.Any suggestions? Much appreciated.

author: bdunham7
author_rank: Super Contributor
timestamp: January 06, 2022, 09:33:44 pm
content: First, get a USB stick so you can do a screen print and then post the PNGs here. It is much neater and easier to see and understand.Try doing a single-shot acquisition and see what your signal looks like under various conditions--exactly as you have it there, with a lower-level signal, with no signal and then the scope disconnected. There's enough noise there that I would expect the scope to trigger on that alone. Then you should expand the noise out and see what it looks like and what frequency it is. Have you tried multiple signal sources?

author: IAmBack
author_rank: Regular Contributor
timestamp: January 06, 2022, 09:49:31 pm
content: What can be seen if probe is shortened (ground connected to the probe tip)?

author: tautech
author_rank: Super Contributor
timestamp: January 06, 2022, 10:33:11 pm
content: I'd lay money it's RFI from your LED lighting or a SMPS wallwart nearby.

author: Agosto
author_rank: Contributor
timestamp: January 06, 2022, 10:43:33 pm
content: Thank you all for your responses! I am working on making myself familiar with the scope including the downloading of images to a USB stick. Sorry for that!If I short the probe I have a high frequency noise floor of about 1mV (see photo). I tried three different probes and the two provided with the scope are the worst. So I am thinking of getting better quality probes (?).I have an LED shop light above my work bench.Switched it off - no difference.Thanks again

author: tautech
author_rank: Super Contributor
timestamp: January 06, 2022, 10:54:26 pm
content: Quote from: Agosto on January 06, 2022, 10:43:33 pmThat's a different screenshot with vastly different settings and what you see is just system noise at highest input sensitivity. There's nothing wrong with the probes.....increased noise just demonstrates their sensitivity.Use the blue Print button to capture screenshots to USB.

author: Agosto
author_rank: Contributor
timestamp: January 06, 2022, 11:15:25 pm
content: OK will do. Will upload tomorrow.

author: tautech
author_rank: Super Contributor
timestamp: January 06, 2022, 11:25:55 pm
content: Quote from: Agosto on January 06, 2022, 11:15:25 pmSome things to experiment with to learn more about the capabilities of these fine little DSO's:Try GND input coupling.Experiment with the differences between 1x and 10x settings on the probe and input attenuation.Keep an eye on the channel tab to be sure your probe and input settings match.Practice displaying the menu most relevant to settings you are trying to convey.For the bulk of scope use we use 10x probes and input settings, become familiar in quickly identifying how you have the scope setup. Use the 1 KHz 3V p-p probe compensation output as your first sanity check.When initially coming to a DSO one must get out of the habit of looking at the controls where instead all the info of how your scope is setup is on the display.Have fun with it as they're a very popular model, yours is a SDS1104X-E, right ?

author: Performa01
author_rank: Super Contributor
timestamp: January 07, 2022, 01:22:15 pm
content: Well, what do you expect from a passive high impedance probe in a noisy environment, when looking at the input signal with a 500µV/div vertical gain - a true full resolution full bandwidth sensitivity that very few other scopes have?Shorting the ground lead to the probe tip doesn't help, this just forms a magnetic loop antenna for high frequencies. The same happens everytime you're probing a low impedance node in your DUT. If you really need to probe signals that low, then use the supplied ground spring to keep that loop as small as possible - and use the bandwidth limiter whenever possible.You can also have fun with your loop antenna though: try sniffing different locations on your bench, other instruments or TFT screens - also the one of your scope - with this loop antenna and see if you can find some interesting looking signalsDisconnect the probe, then the scope should reveal its own noise. For the SDS1104X-E this should be about 460 µVpp and 63 µVrms AC-RMS (Standard Deviation).With the 20 MHz bandwidth limit, these figures should go down to 200 µVpp and 28 µV Stdev.Higher bandwidth probes can make the noise pickup worse. But the 20 MHz bandwidth limit helps a lot and whenever super high sensitivities like 1 mV or less really are required, then the bandwidth limit usually is no real limitation for the vast majority of such tasks.

author: Agosto
author_rank: Contributor
timestamp: January 07, 2022, 03:05:15 pm
content: Thank you for your replies. The reason I selected the 500uV vertical gain was only to better visualize the noise when shorting the probe.. My real issue is (see beginning of my post) that I have this high-frequency noise image on e.g. a 1kHz signal. Connecting the probe to my old analog scope shows a clean image.I am still working on all the suggestions I received and being a newbie with these digital scopes I am still in the process of understanding the menus and the principal setup by reading the manual.I also have not yet figured out how to download an image to a USB device. Looks like I need to download a USBTMC device driver before I can do that. I am using a Mac and the .xml files are opened in a text editor mode which does not result in the image stored.As I said: I am still learning so I appreciate your all patience!

author: bdunham7
author_rank: Super Contributor
timestamp: January 07, 2022, 03:21:13 pm
content: Quote from: Agosto on January 07, 2022, 03:05:15 pmAnd we need to know what the source of that signal is, and if you have any other signal sources that you can use for comparison. Then we can tell you how to use your new scope to further analyze the noise.QuoteYou simply insert the USB drive into the USB connector on the front of the scope and press the blue 'PRINT' button. The scope will create a folder on the drive and store .png files on it. It should do this right out of the box, nothing needs to be installed. The USB drive needs to be FAT32 formatted, but most are so that's usually not an issue.

author: Fungus
author_rank: Super Contributor
timestamp: January 07, 2022, 03:53:34 pm
content: Quote from: Agosto on January 07, 2022, 03:05:15 pmDSOs are much better at showing noise than "old analog 'scopes".

author: 2N3055
author_rank: Super Contributor
timestamp: January 07, 2022, 04:00:40 pm
content: Quote from: Agosto on January 07, 2022, 03:05:15 pmSince you're beginner, a bit of repetition won't hurt.First, it doesn't matter if scope is digital or analog for this particular purpose. You keep comparing what you see to your old CRT scope but you never said which one it is. That would help us compare and give you best advice. It probably has much less bandwidth (max frequency it can see and show on a screen), and less sensitivity (how small signal can it show on screen in large size). We need information to troubleshoot at distance..Despite being entry level scope SDS1104X-E has lot of bandwidth and sensitivity, only few best old CRT scopes had..Like Performa001 said try enabling 20 MHz limiter. Was your old scope also capable of showing 200 MHz signals?What was old scope best sensitivity: 10mV/div, 5mv/div?Set new Siglent to same sensitivity and enable 20MHz limit and note what you see then..Measuring low signals at high bandwidth is an art.Imagine how it looks when I do same thing as you with a scope that also have 500uV/div and more than 1GHz bandwidth... There are no phones allowed in my lab when I measure something. There is no WiFi either.LED lamps are either off or selected for low EMI...Despite all that, at these sensitivities I can clearly see local FM radio station (transmitter is 20 km away) if I use passive probes. Unless you use fully coaxial connections, shielded DUT etc.. you will see anything from your ambient.That is why EMI measurement labs have these large shielded chambers build (that and the fact is that they are anechoic so they don't reflect and resonate) so they can measure with some certainty...

author: 2N3055
author_rank: Super Contributor
timestamp: January 07, 2022, 04:10:07 pm
content: Quote from: Fungus on January 07, 2022, 03:53:34 pmNo No NO.That is not it. Don't confuse the guy. You're not wrong, it is just off topic here.EDITI frequently joke that noise is "object oriented". That is, it the most overloaded word in electronics.Noise from stochastic processes is THE noise.But unfortunately, people got to use the term "noise" for anything that is not the signal. That includes interference, crosstalk, anything. Local radio station is noise, spurs are noise, they call everything noise. So it is all called noise now.That is why we have thermal noise, popcorn noise, deterministic, nondeterministic ... all kinds of categories.OP here speaks about high frequency signal superimposed (injected, whatever) on top of what he thinks should be clean 1 Khz sinewave. There are cleanly visible high frequency spikes. His old CRT scope doesn't show them. There it looks clean.

author: modoran
author_rank: Regular Contributor
timestamp: January 07, 2022, 04:13:30 pm
content: In the picture posted this is not SDS1104X-E, USB port is placed differently.

author: Fungus
author_rank: Super Contributor
timestamp: January 07, 2022, 04:16:19 pm
content: Quote from: 2N3055 on January 07, 2022, 04:10:07 pmOP hasalsospoken about noise with no input signal.Here.The two things are related. In that video Dave also talks about not being able to see very short spikes on analog 'scopes.

author: 2N3055
author_rank: Super Contributor
timestamp: January 07, 2022, 04:27:21 pm
content: Quote from: modoran on January 07, 2022, 04:13:30 pmSDS1202X-E

author: 2N3055
author_rank: Super Contributor
timestamp: January 07, 2022, 04:30:08 pm
content: Quote from: Fungus on January 07, 2022, 04:16:19 pmFair enough... I didn't see that.. My bad. I apologize.But still these are two different problems with different causes.You provided good answer to second one, regarding internal noise.High frequency interference is separate topic.

author: Fungus
author_rank: Super Contributor
timestamp: January 07, 2022, 04:39:31 pm
content: Quote from: 2N3055 on January 07, 2022, 04:30:08 pmYep. No argument there.His analog 'scope probably isn't showing show those thin spikes on his signal even though they're there.

author: Agosto
author_rank: Contributor
timestamp: January 07, 2022, 04:54:51 pm
content: Thank you for the continued feedback. Meanwhile I was trying to eliminate (or limit) the high frequency distortion by disconnecting all available and possible sources (power supplies, lighting, other test equipment,..) without great success.I guess "2N3055" is right when stating that my old analog scope does not have the bandwidth to show these high frequencies, thus resulting in a "clean" image.The high frequency distortion is not stable, it fluctuates and occasionally disappears. Playing around with the ground connection alters the image as well. So I guess the distorted image is a combination of these two (plus other) effects. The 20MHz limiter does not bring visible improvement.I am mostly working with NF signals (audio repairs) where test voltages/signals may go as low as a few mV. Hence a clean imaging is really important. So I guess I will continue to play around and gain more knowledge in working with a digital, high bandwidth scope.Can somebody recommend me a source for good test probes? I think the ground clamping on the probes supplied by the scope manufacturer is not the best solution and contributes to the issue.@bdunham7: Thank you for the "Print" advice. I tried that before based on an earlier input but that failed due to a bad stick. Tried it again - works fine.Once again: Many thanks to all!!

author: bdunham7
author_rank: Super Contributor
timestamp: January 07, 2022, 05:59:14 pm
content: Quote from: Agosto on January 07, 2022, 04:54:51 pmIt looks like the periodic rate of your interference or undesired signal is about 25kHz or so, but you would have to expand your trace to see what it looks like and what bandwidth it has, IOW how short the spikes are vs how often they occur. I also work with audio and low-level signals and I'd recommend you be a bit cautious about what you conclude. "Clean imaging" can be often accomplished with techniques like BW limiting and averaging, but it may be deceptive--those spikes might be interference in the scope circuit only and not matter to your device(s) or it may be a signal that is actually there throughout. Instead of treating this issue like a nuisance, use it as an opportunity to learn about your new scope and appropriate probing techniques. A description of your signal source and a photo of how you have everything hooked up would be helpful as well.If you got the PP215 probes with the scope, they are absolutely fine. Perhaps not industrial quality, but performance wise there's no reason to be looking for replacements. The low-level noise you see at the 500uV/div level is of no importance to your original question and the random changes in that noise with different probes and positions is also unimportant. For audio-level signals, I recommend you get some breakout cables that go from BNC to alligator or extendable hook tips.

author: Agosto
author_rank: Contributor
timestamp: January 07, 2022, 06:16:07 pm
content: Thank you for your recommendation. Re the breakout cables: I already have those

author: Fungus
author_rank: Super Contributor
timestamp: January 07, 2022, 06:28:29 pm
content: Quote from: Agosto on January 07, 2022, 04:54:51 pmIt happens to everybody:

author: tautech
author_rank: Super Contributor
timestamp: January 07, 2022, 07:57:25 pm
content: Quote from: bdunham7 on January 07, 2022, 05:59:14 pmExactly why I mentioned SMPS RFI in an earlier post.I've seen this before with owners new to such scopes where they have been insistent there's a problem with the scope whenalwaysit's instead some nearby wallwart or such spewing garbage to mess with measurements.The only way to find such little bastards is to go right through the house turning everything unneeded OFF.It's not uncommon it's found yards away or even in another room.

author: Performa01
author_rank: Super Contributor
timestamp: January 07, 2022, 09:41:36 pm
content: Quote from: Agosto on January 07, 2022, 04:54:51 pmIf different positions and different orientations of the probe change the superimposed high frequency signal, then it's very likely not coming from your DUT.In that case you can try to clean the signal by using the ERES and Average acquisition modes.Average does not reduce the input bandwidth, but it supresses any modulation. So it is only usable on static signals with asynchronous interferences.ERES is a digital lowpass filter with a sample rate dependant corner frequency. If you're dealing with audio, then about 6.7 MHz bandwidth at full sample rate (500 MSa/s or 1 GSa/s, depending on activated channels) should be plenty, so you can use ERES with 3.0 bits.More info on the various acquisition modes and most other functions can be found in the documents attached here:https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-in-depth-review/

author: Agosto
author_rank: Contributor
timestamp: January 07, 2022, 10:26:43 pm
content: Perfect - Thanks!