How to choose an oscilloscope for checking EMI? - Page 1
Forum section: electronics / testgear

author: kayasaman
author_rank: Contributor
timestamp: August 12, 2025, 10:07:53 am
content: Hi everyone,I'm about to start getting in to building drones (civilian / recreational / hobby types) and hope to work my way up to larger cinelifter types that can carry full frame cameras.There will be a lot of soldering needed (woohoo!) but also debug / troubleshooting; and the one thing that I see frequently talked about is electromagnetic interference which does affect things like compasses and other types of sensors susceptible to changes in magnetic fields.I basically need a multimeter for various tests (continuity is highly important) and scope to verify signal output.I researched this a while back and found that I liked the Bryman and Hioki meters the most and after narrowing things down found Hioki to suite my needs best. I'll need to recap on things but I'm probably going to go for a DT4282 there.For scope I have no ideaI did stumble on a post here in the EEVBlog forum, where someone made a list of Tier 1? Chinese branded models with a price point being in the $100-200 range. I did think that was quite low as from memory I recalled scopes being around the $1000 mark at their most basic....In the comments someone pointed out some Tier 2? brands like: Micsig, Regol, and Siglent. 20 years ago when I was at university studying electronics I recall we had a Tektronix LCD scope - I think a 2-channel monochrome version which I think was at the dawn of LCD's instead of the stuff that we used mostly being Tektronix and HP CRO's.I'm looking through this currently:https://www.keysight.com/used/gb/en/knowledge/guides/used-oscilloscope-buying-guide/15-features-you-should-look-for-before-buying-an-oscilloscopemost of the signals are going to be Serial type signals using either TTL or RS232 style signalling, or PWM based. The flight controllers normally have a lot of UARTs and some bus outputs depending on model.I don't have a lot of space on my workbench so I was considering something like a handheld scope or possibly one of the what looks like ultra slim scopes from Tektronix or Micsig.The voltage levels I will be working with will be between ULV to LV levels and mainly DC. I guess anything up to 200MHz bandwidth will be fine as I don't see the need of going up to 1GHz as I don't really plan on doing any RF or high frequency stuff.Looking at things more closely the Siglent SHS series might be an option, and maybe the Micsig STO / SATO / ETO or MHO3 series, or Tektronix 4Series or 5Series or MDO versions (couldn't find pricing yet as the store I looked at doesn't say anything) might be what I'm looking for.Any suggestions would be highly appreciated!

author: 2N3055
author_rank: Super Contributor
timestamp: August 12, 2025, 11:23:48 am
content: For EMC you really need a spectrum analyzer of a sort.Modern scopes with good FFT will show you stuff in their BW. That is some 200 ish MHz max. for affordable scopes.Even a small TinySA will go to GHz region and will be plenty for you to get you started.You might want a set of inexpensive near field "sniffer" probes. Or make them DIY style. Plenty of information on that.That combination might help you find sources of radiation, but they will not be in any way representative what device would look like in real far field test in EMC lab.But they will help you understand your devices and what is happening there. Of course, after you learn how to do it.For scopes, you have Rigol DHO800 and Siglent SDS800xHD as very affordable, but still "real scopes". I personally would not go below that.DHO800 is slightly thinner and has USB-C external power. It is also less capable of the two.Some like it some don't.SDS800xHD has internal power (like a real instrument that is!) it has less tall but a bit deeper case.It has very advanced mathematics and measurements. It is very good device.When combined with Siglent AWG (any type from manufacturer) it can do frequency response (gain/phase plots, Bode plots) analysis.Some like it some don't.Both scopes are miles better than Tek you remember.If you really need portable, Siglent scopemeters are good, and also Micsig has tablet format.Do your research and decide.

author: pdenisowski
author_rank: Super Contributor
timestamp: August 12, 2025, 11:39:34 am
content: Quote from: 2N3055 on August 12, 2025, 11:23:48 amYes, you absolutely need some kind of frequency-domain / spectrum analysis capability - the speed / usability of the FFT function on a scope would be, by far, the most important feature I would be looking at.And yes, you also want near field probes, especially H-field / loop type probes. As 2N3055 mentioned, these can be easily home-brewed.I did a short video on precisely this topic (some parts would not apply to this application though):and one one near-field probes

author: TERRA Operative
author_rank: Super Contributor
timestamp: August 12, 2025, 11:49:19 am
content: And while you are looking into EMC probes, also have a look at EMC test cells and EMI RF Shielded Tent Enclosures.You may need something like this to do pre-compliance testing

author: kayasaman
author_rank: Contributor
timestamp: August 12, 2025, 12:08:14 pm
content: Hmm.... that gives me something to think about!! Thank you both :-)Yeah as pointed out research is key here of which I haven't done much of as I had no reference point. All I was thinking is view the output in "time domain" and see if there's any "ripple" effect on the crest of the waveform and rise and slope areas, then using the 'drone builder practical mentality' start moving the sensors away from the battery leads (main source of EMI) and see when you get to a cleaner signal.For my final year project I used an HP Frequency Analyzer with a very cool green on black CRT display. One of my favorite analysis tools, though I was in the audio domain 20-20KHz which the project was essentially based off of acoustics and acoustic response within different mediums etc...Similar kind of questions here to mine:https://www.eevblog.com/forum/testgear/i-recommend-choosing-a-combo-oscilloscope/https://www.eevblog.com/forum/testgear/handheld-scope-with-fft/One recommendation was the DHO800. I wonder is it better to get a separate scope and analyzer, combined scope and analyzer or an FFT scope? I'll also research "near field probes" as I have never used them before... I only used the crock clip style probes or the pointy ended ones like multimeters have.I guess the main emphasis for the university at the time was teaching the mathematics necessary to understand things like Fourier and LaPlace analysis - of which I remember nothing todayBasically this is the kind of stuff I am trying to get started with for now:https://oscarliang.com/how-to-build-fpv-drone/

author: 2N3055
author_rank: Super Contributor
timestamp: August 12, 2025, 01:26:05 pm
content: I reread OPs post, and would like to add:If this is really with emphasis on very low frequency EM fields, you might need some fluxmeters that go to DC, i.e. to permanent fields.For low frequency EM fields, there is a specialty tool from AIM-TTI in UK.It is called I-prober 520, which is a DC-5MHz magnetic field probe.I have been eyeing it for a long time, never pulling the trigger..It is VERY interesting and unusual probe.

author: 2N3055
author_rank: Super Contributor
timestamp: August 12, 2025, 01:30:06 pm
content: Quote from: kayasaman on August 12, 2025, 12:08:14 pmRigol DHO800 is neither handheld nor it's FFT is best.SDS800xHD has more elaborate FFT implementation. Both are benchtop instruments.For handheld you need SHS800/1000 from Siglent (or more expensive from big brands) or Micsig, that is fat tablet so it is kind of handheld.

author: kayasaman
author_rank: Contributor
timestamp: August 12, 2025, 02:19:59 pm
content: Quote from: 2N3055 on August 12, 2025, 01:30:06 pmThank you, sorry I probably phrased things wrongly and should have said either - small footprint Benchtop or Handheld.I'll take a look at the fluxmeter you mentioned: I-prober 520 too.I just watched both @pdesinowski's videos which was really interesting. It got me thinking a little bit when using H or E field probes, in that does one then need an in-phase FFT?I'm going through this topic right now:https://www.eevblog.com/forum/testgear/oscilloscope-for-fft-functions/which discuss about "phase information" and suggests that the scopes that retain this are in higher tier levels from what I am looking at.Though they recommend the GW Instek GDS-1000B or 2000E having the best "budget" FFT capability:https://www.gwinstek.com/en-global/products/detail/GDS-1000BInteresting.... the I-probe is an actually probe that connects to a scope:https://www.aimtti.com/product-category/current-probes/aim-i-prober-520Oh ok I see now.... it is an H-field probe :-)

author: kayasaman
author_rank: Contributor
timestamp: August 12, 2025, 02:31:41 pm
content: Actually what's a bit embarrassing for me and the reason I'm asking for either handheld or small footprint bench top device is that this is the amount of space I have got to work with.Sadly I live in a very squished and small country with heavy over-population, meaning that space is a premium no matter where you go; which is enough to give anyone claustrophobia

author: 2N3055
author_rank: Super Contributor
timestamp: August 12, 2025, 02:52:57 pm
content: Quote from: kayasaman on August 12, 2025, 02:31:41 pmThere is plenty of space here for both DHO800 and SDS800xHD.

author: oz2cpu
author_rank: Frequent Contributor
timestamp: August 12, 2025, 03:06:46 pm
content: see this videohttps://youtu.be/M_57a7WzHCQSiglent SSA3021X at emc lab, using EMC settings, sweep time comparedSiglent SSA3021X wins 1.1 secRohde & Schwartz ESCS 30 looses 20 minswe made 23 measurements today,so that is 460 mins (7½hrs) saved by the SSA3021X, thanks Siglent..

author: kayasaman
author_rank: Contributor
timestamp: August 12, 2025, 03:27:09 pm
content: Quote from: oz2cpu on August 12, 2025, 03:06:46 pmIs the SSA series an older model lineup? All I see on the website under Oscilloscopes is the SDS series...Going to @2N3055's suggestion of the SDS800x series I am currently looking at this model:siglent-sds824x-hd-4ch-200mhz-2gsa-s-12-bit-hd-high-resolution-oscilloscope/which seems to feature:* Serial bus triggering and decoder, supports protocols I2C, SPI, UART, CAN, LIN Fitted as standard.* Provides 4 Math traces with options for FFT, addition, subtraction, multiplication, division, integration, differential, square root, etc., and supports formula editing* Provides various interfaces including USB Hosts, USB Device (USBTMC), LAN (VXI-11/Telnet/Socket), Pass/Fail, and Trigger OutThat's good news to me as UART and CAN bus is interesting! Does decode mean that it can read information at the data or application level? I'll start digging through the manual in a second though it would be kinda interesting to have the scope read and understand stuff like NMEA 0183 sentencesAlso it features a LAN port and telnet input which is great, meaning there are commands to be run and information to be received.

author: nctnico
author_rank: Super Contributor
timestamp: August 12, 2025, 03:28:16 pm
content: Quote from: oz2cpu on August 12, 2025, 03:06:46 pmI think that is because the ESCS has quasi peak enabled. That is a slow measurement to do. At the EMC lab I visit every now end then, they only do quasi peak on suspect frequencies (at worst case angle) after scanning the DUT at various angles, not the entire sweep for every measurement.

author: 2N3055
author_rank: Super Contributor
timestamp: August 12, 2025, 04:57:56 pm
content: Quote from: kayasaman on August 12, 2025, 03:27:09 pmSerial protocol decoding means it will decode addresses and numerical/hex/ASCII data payload, together with checking acks, checksums and all kinds of malformation errors.Symbolic decoding (where you map CAN message 334_100 to Throtlle position 100%) is reserved to much more expensive devices, sorry.Before finally comitting to the SDS800xHD you can check this topic :https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293741/#msg5293741It is absolute gem of info on the scope.

author: kayasaman
author_rank: Contributor
timestamp: August 12, 2025, 05:08:29 pm
content: Quote from: 2N3055 on August 12, 2025, 04:57:56 pmThank you so much!! I am actually just reading the manual right now on UART decode :-)It gives you information similar to the OSI stack model layer 2 and 3 (data and link layers)Do you know how many points the FFT gives? I can't find it in the specs on the website - maybe it's in the manual? I just want to compare it to the GW GDS-2000E which has up to 1M points

author: kayasaman
author_rank: Contributor
timestamp: August 12, 2025, 05:21:32 pm
content: Bit confusing but I wonder if this means 2Mpts?Code:FFT sample rate (Sa): FFT operation results present the first Nyquist zone (DC ~ Sa/2) of thefrequency spectrum. Be aware that the FFT sample rate may be inconsistent with the samplerate in the time domain. Assuming the max points value is set to 2 Mpts:✓ When the number of points in the time domain, N, is less than 2 Mpts, the FFT takes thenumber which is an integer power of 2 closest to N. In this case, FFT sample rate = samplerate in the time domain.✓ When N is greater than 2 Mpts, FFT first decimates N by D and then takes the first 2 Mptsfor the calculation. In this case, FFT sample rate = sample rate in time domain/D.For example, in the case of sample rate in the time domain is 2 GSa/s and the number ofsamples is 10 Mpts, the FFT first decimates the samples by 4, to 2.5 Mpts, and then takesthe first 2 Mpts to calculate the spectrum. In this example, FFT sample rate = 2GSa/s ÷ 4 =500 MSa/s Reading on it definitely says 2Mpts:Code:FFT points (Curr): The current FFT points, which is an integer power of 2. The SDS800X HDsupports up to 2 M points (2097152, to be exact).

author: 2N3055
author_rank: Super Contributor
timestamp: August 12, 2025, 05:23:18 pm
content: Quote from: kayasaman on August 12, 2025, 05:21:32 pmYes.Check datasheet

author: kayasaman
author_rank: Contributor
timestamp: August 13, 2025, 01:47:45 pm
content: I've just gone through the link provided by @2N3055 and it contains a very in-depth amount of information, which mostly was quite advanced for my understand level as I haven't done this stuff for a long time and of course never used such an advanced type of scope.I really liked the information of the FFT analysis and the Serial stuff using the SLA1016 SBUS breakout connector.One thing though that sticks out is the lack of 50ohm impedance on the inputs of the SDS800X series. From Paul's video above he discusses that the probes usually pickup very low level signals either requiring a low impedance input or some kind of inline amplification.I have been looking at the SDS824X-HD but I wonder if it's worth spending a little bit more money and going for the SDS1204X HD model?The i-Prober H-field probe seems to have a power amplifier in any case so that means it will be fine with the 824 so that's fine.Though I did find these probes from Siglent: SRF5030T Near-Field Probe which are passive and you get 3x H-field and 1x E-field.For now I'm just searching for data interpretation as in how things will look on the scope in Frequency domain. This video shows the angular component of the EM propagation:I'm a little confused as to where the EM part lies? Just re-watching at around 5.50 there is a higher power in the lower frequency range so I'm guessing that, this is where the EM noise resides.So if the probe is placed around one of these modules:One should see a higher amplitude of low frequencies indicating that there is EM noise, thus throwing the compass readings off?Just stumbled across this video and it was more along the lines of what I envisioned initially though in a completely different context by using a CNC machine:The tests at the end on insulating certain portions of the wiring and their various effects was also particularly interesting.

author: pdenisowski
author_rank: Super Contributor
timestamp: August 13, 2025, 03:26:02 pm
content: Quote from: kayasaman on August 12, 2025, 02:19:59 pmFor EMC, phase information is generally unimportant - you simply are looking at a power as a function of frequency. Ultimately, the primary goals are to identify emissions (intentional or otherwise) that could cause problems to nearby devices and then locate the physical source of those emissions.Quote from: kayasaman on August 13, 2025, 01:47:45 pmIn my experience the most important thing is the noise / sensitivity at the scope input - if the "undesired" signal you're looking for is beneath the noise (so to speak), you won't be able to find it. Some near field probe sets (ours and others') have an optional preamplifier that usually eliminates most concerns about noise / sensitivity - if you can't see the spur with a preamp, it's probably not much of a spurIf the lack of 50 ohms concerns you, you can get a 50 ohm feedthrough fairly cheaply - I use these regularly on our (R&S) entry-level scopes that also don't have 50 ohms and they work just fine. But again, this probably won't be a significant concern for EMC testing.