Need some help deciding on oscilloscope's specs. - Page 1
Forum section: electronics / beginners

author: Sycc90
author_rank: Newbie
timestamp: October 29, 2017, 11:19:17 pm
content: Greetings everyone, this is my first time here so I hope you'll be nice to me =)Now before anything else I want to say I have been reading the forum, I have watched Dave's videos and reviews on the subject and I have found a TON of information here regarding this. However, this is still the first time I'm buying an oscilloscope for myself and it's a big purchase (they're particularly expensive where I live and bringing them from abroad is not really an option) so I figured you could help me figure this out.Taking into account what's available here where I live and my budget I've narrowed it down to basically 3 options. I'm not going to put a number on my budget because, like I said before, they're quite more expensive than the usual sites I see people buy them from (I'm from Argentina), for example, de DS1054Z is $700~800 and I know you can get it at $400 almost anywhere else. In any case, I've narrowed it down to:1) Rigol DS1054Z2) GW-Instek GDS-1054B3) GW-Instek GDS-1072BBoth 1054 are the same price and the 1072B is about 20% less. There's also the 1102B at basically the same price (7% less than 1054, that's about 50-60 bucks). I don't think I'm gonna be hacking the Rigol, at least not while the warranty is running, I know I could do it a couple of years down the line if I need to but I'm not sure what my needs are going to be then, I might just sell whichever I buy now and get a new (better) one.What I mostly need to figure out is whether to get 4 channels at 50MHz or 2 channels at 70MHz.A bit of background about myself. I'm an electronic engineer and have used a couple of scopes at work, although those were LeCroy and Agilent mid-top of the line so it's kind of hard comparing. Still, I haven't used them much because most of my work is FPGAs and microcontrollers and the surrounding bits of the system are designed by other people so I can usually trust that they work (when they don't is the few times I've had to use the scopes).I don't have a particular field I'm going to be using it in, this is mostly for hobby projects and will most likely involve microcontrollers (and maybe lowend FPGAs eventually). I just moved into a bigger apartment and I can finally have some space for a small home "lab" so I wanted to start by buying a couple of things (mostly a soldering station, power supply and scope), I would like to get a scope I know will work good enough for a wide variety of projects.I also had a look at some Owon scopes (SDS7102) but after reading reviews about it here and watching a couple of videos I decided against them.So to sum up, I'm trying to figure out whether less channels but higher bandwidth is better than more channels at less bandwidth. I'm pretty well aware it depends on the application, and that's exactly why I'm here, since I don't have a specific application in mind I was hoping you guys (who have a lot more experience than I do) might help me decide which I should go for as my first "general purpose" scope.Thank you all for your time!Regards,-- Sycc

author: rstofer
author_rank: Super Contributor
timestamp: October 30, 2017, 01:01:11 am
content: Unlocking the DS1054Z gives you 100 MHz and a lot of features. It is reversible if you're worried about warranty. I would bet that it has been done by nearly every person on this forum who owns one.That makes the DS1054Z a legitimate 100 MHz scope with 4 channels and decoding. You should consider these features as a given when comparing to other low end scopes. FFT is not impressive.I have heard good things about GW-Instek (mostly from user nctnico, he posts over in the Test Equipment forum quite a bit).I own the DS1054Z and it works well. I am considering the new Siglent SDS1204X-E as soon as it is released. Presumably the scope will cost about $500 and have 4 channels and 200 MHz bandwidth with all decoding options factory enabled. It should become a best seller! More over in the Test Equipment forum.

author: ebclr
author_rank: Super Contributor
timestamp: October 30, 2017, 01:02:11 am
content: Rigold DZ1054Z 510 USD with freight to Argentinahttps://pt.aliexpress.com/item/RIGOL-DS1054Z-50MHz-Digital-Oscilloscope-4-analog-channels-50MHz-bandwidth/32747617970.html?ws_ab_test=searchweb0_0,searchweb201602_1_10152_10065_10151_10068_10130_10344_10345_10547_10342_10343_10340_5620011_10341_10548_10545_10541_10307_10060_5700011_10155_5640011_10154_5370011_10056_10055_10539_10538_10537_10536_10059_10534_10533_100031_10103_10102_10142_10107_5760011_10324_10084_10083_10178_10312_10313_10314_5750011_10073_5630011-10102_10152_10151,searchweb201603_17,ppcSwitch_5&btsid=84c8967f-1ccf-471e-b2d8-a582b5ff4a7c&algo_expid=06a8704b-ff5a-407b-9fc9-0748afdda222-10&algo_pvid=06a8704b-ff5a-407b-9fc9-0748afdda2222,searchweb201603_17,ppcSwitch_5&btsid=84c8967f-1ccf-471e-b2d8-a582b5ff4a7c&algo_expid=06a8704b-ff5a-407b-9fc9-0748afdda222-4&algo_pvid=06a8704b-ff5a-407b-9fc9-0748afdda222Don't worry about the hack/warranty, is easy and reversible, also I beat that no real warranty is available in Argentina, other than sending back and pay a lot on freight

author: tggzzz
author_rank: Super Contributor
timestamp: October 30, 2017, 01:24:24 am
content: One systematic approach with digital circuits isuse a scope to verify signal integrity, so that the analogue circuits in the FPGA (yes, really) can correctly interpret the analogue voltages (yes really) as digital signalsthen switch to the digital domain and use a logic analyser of printf() statements to debug the digital signalsVerifying signal integrity requires the highest bandwidth, decent probes (e.g. resistive divider Z0 probes), and sound probing technique. 100MHz was adequate for LSTTL, back in the early 80s, when the transition times were ~5ns. Modern jellybean logic has sub-nanosecond transition times.

author: ebclr
author_rank: Super Contributor
timestamp: October 30, 2017, 01:31:01 am
content: The key point is sample rate, and all low-cost scopes don't pass the 1GS mark, the better deal is the more channels because you always can disable 2 channels or even 3 channels and get all sampling only for one channel.It's simple 4 is more than 2 for the same sample rate,

author: Sycc90
author_rank: Newbie
timestamp: October 30, 2017, 02:58:08 am
content: Quote from: ebclr on October 30, 2017, 01:02:11 amThank you for taking the time to look that up, however the problem is not buying it but getting it into the country (taxes, expenses, getting through customs it all ends up to a few hundred dollars more).What about the FFT on the Rigol? I watched a video Dave made comparing them and it was terrible, but I do read it has improved with newer firmware.

author: ebclr
author_rank: Super Contributor
timestamp: October 30, 2017, 04:09:24 am
content: FFT is the basics, but on the PC side, have some free software that does quite nice

author: tggzzz
author_rank: Super Contributor
timestamp: October 30, 2017, 08:18:54 am
content: Quote from: ebclr on October 30, 2017, 01:31:01 amThe sampling rate is ofsecondaryimportance; thefront-end bandwidthis of primary importance. The sampling rate is little more than a marketing gee-whiz number - its primary benefit is to simplify anti-aliasing filters, not to allow you to observe fasted signals.If you doubt that, look at the spec for professional scopes. A while ago I used a top-of-the-range HP scope to characterise sub-nanosecond risetimes; that scope was 25MS/s. I currently use a scope with >2.5GHz bandwidth to characterise impedance variations; it has, IIRC 10kS/s.

author: Sycc90
author_rank: Newbie
timestamp: October 30, 2017, 08:03:27 pm
content: Quote from: ebclr on October 30, 2017, 01:31:01 amThat's true, however there's also the difference in price. I'm actually a bit over budget going for either of the 4 channels one so I also want to figure out whether 4ch @ 50MHz es worth the extra cost over 2ch @ 70MHz.

author: Sycc90
author_rank: Newbie
timestamp: October 31, 2017, 06:04:02 pm
content: I want to thank you all for your comments and input, but in the end it was decided for me. None of the local distributors have the Rigol in stock nor are they planning on importing them any time soon, so I've decided to go for the GDS1054B, I think having 4 channels will be a lot more useful than 100MHz of bandwidth.

author: tggzzz
author_rank: Super Contributor
timestamp: October 31, 2017, 06:15:55 pm
content: Since you may not be able to demonstrate the absence of signal integrity problems, you may think it prudent to take precautions to ensure thereareno such problems.Good engineering is, to a large extent, avoiding problems.

author: Sycc90
author_rank: Newbie
timestamp: October 31, 2017, 07:40:35 pm
content: Of course, you're absolutely right about that.After thinking about it for a while I realized that to verify signal integrity I'd probably need quite a lot more bandwidth than either 50 or 100MHz. Sure, there might be some specific cases which fall right into that gap, but I don't think that'll be the case most of the time. Specially since microcontrollers make a huge leap between really basic 8-bit ones (8-16MHz) to the big 32-bit ones running at 100MHz or more. And with usually much faster edges than I'd be able to measure either way.Edit: going back in the thread, that's exactly what you mentioned on your first post, that current technology (and not top of the line) has much faster edges than I'd be able to measure with any of these entry-level scopes. I guess I didn't think about it on my own but my brain just pondered on what you had said without realizing it =P

author: khs
author_rank: Regular Contributor
timestamp: October 31, 2017, 09:54:11 pm
content: Quote from: Sycc90 on October 30, 2017, 08:03:27 pmFrom my experiences, definitively yes.By example, a four channel oscilloscope can be used as a (simple) logic analyzer too. In many cases the correlation between the signals is more important than the waveform.The difference between 50 MHz and 70 MHz is not much. To verify signal integrity more than 200 MHz BW (and a good probe) is required. But a FPGA don't make glitches - as long as your wires on your board are not too long. A FPGA makes nonsense, if there is a bug in the code (Exceptions prove the rule).

author: tggzzz
author_rank: Super Contributor
timestamp: October 31, 2017, 10:12:01 pm
content: Quote from: Sycc90 on October 31, 2017, 07:40:35 pmIt is always a pleasure to come across someone thatre-reads andthinks. That makes it worth writing something in the first place

author: ebclr
author_rank: Super Contributor
timestamp: November 02, 2017, 02:22:37 am
content: It' s impossible to measure a single cycle 2 Ghz with sample rate of 1Ghz, even if god make the front end for infinite bandwidth, Sample rate and front end must be matched otherwise is wasting resources in one of those

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2017, 09:12:59 am
content: Quote from: ebclr on November 02, 2017, 02:22:37 amAh, I see your problem: you are only considering a limited range of how scopes can beand areused.You should consider and understand a use for which scopes areuniquelysuitable: assessing signal integrity. Understanding why decent manufacturers prominently show eye-diagrams in their advertising will help in that respect.Perhaps you should look atthis pictureof a 1960 scope, and ask yourself what the sampling rate is. I recently played with one at a Maker Faire which was measuring a 700ps risetime with ease.Finally, I presume youdoknow what is the minimum sampling rate to fully recover a 10kHz signal on a 1GHz carrier.

author: Sycc90
author_rank: Newbie
timestamp: November 02, 2017, 11:32:56 am
content: Quote from: tggzzz on November 02, 2017, 09:12:59 amIsn't that just equivalent-time sampling rate? I don't mean per se, but rather the principle behind it. Since you have a repetitive waveform you just sample a bunch of times (eye diagrams do it randomly, don't they?) and you don't need a high sampling rate.

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2017, 12:19:34 pm
content: Quote from: Sycc90 on November 02, 2017, 11:32:56 amTo all intents and purposes, yes. There are a number of variants, but they don't affect the point.The key point is to disassociate MHz and S/s in people's minds; they are orthogonal concepts. People that conflate them often get the wrong answer to "if I have a 10kHz signal on a 10MHz carrier, how fast must I sample in order to see the signal?". As I mentioned earlier, I have ~2.5GHz scope with a ~10kS/s rate.

author: macboy
author_rank: Super Contributor
timestamp: November 02, 2017, 02:47:00 pm
content: Quote from: tggzzz on November 02, 2017, 12:19:34 pmYour scope is a "sampling" oscilloscope and can not be used for one-shot signals. It absolutely requires a stable, repetitive signal in order to generate a waveform over a relatively long period of time, spanning hundreds to many thousands of cycles of that waveform. This is a special purpose instrument and can be very good at what it can do, but there is a long list of things that it can't do as a result of its principle of operation. Its limitations are similar to those of an analog CRT oscilloscope.Due to improvements in ADC and memory speed, most oscilloscopes these days are "real time" oscilloscopes. A real time scope can capture and display a waveform in one shot (one trigger), at its full bandwidth. This is the only way to capture and view non-repetitive signals. Only the fastest (10's of GHz) scopes will use equivalent time sampling, though many higher end scopes are real-time with an optional equivalent time sampling mode for better detail on high speed repetitive signals.For example, if you want to analyze a clock on your digital board, you can use a sampling scope. If you want to use your scope to view or analyze a serial data stream, you'll need a real time scope. Another example, you might have two uncorrelated signals, like a modulated signal, or an amplifier output that is oscillating. You may not see that with the sampling scope as the oscillations won't be in phase with the signal the scope is triggering on. At best it will show noise on top of a signal.

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2017, 03:04:02 pm
content: Quote from: macboy on November 02, 2017, 02:47:00 pmCorrect.QuoteThat is true of all scopes, and indeed of all instruments.QuoteNonsense. Clearly your experience is limited. Start by considering analogue scopes that store single-shot waveforms without digitising them.QuoteTrue; the advances in ADCs over the past 15 years has been remarkable. But that doesn't affect the point.QuoteI wonder how we managed for the decades before decent ADCs became available? Oh, yes, we used skill and imagination; cue the aphorism in my .sigIn particular, we used scopes and eye diagrams to verify (analogue) signal integrity. Once that was assured, we flipped to debugging in the digital domain with logic analysers and printf statements.That's still a very sound development strategypartly because it works at all speeds not merely the trifling slow-speed stuff like MCUs.QuoteIf you are looking at modulation, you should consider modulation domain analysersIf you are looking at oscillators, scopes are likely to be unrevealing: you need a spectrum analyser with very good phase noise characteristics.Choose the appropriate tool for the job at hand.

author: macboy
author_rank: Super Contributor
timestamp: November 02, 2017, 05:54:49 pm
content: Quote from: tggzzz on November 02, 2017, 03:04:02 pmYou don't need to resort to attacks.It is not nonsense. Or show me how it is. I chose my wording carefully. "similar to", not "identical to".My experience is not "clearly limited".QuoteAnalog storage CRT oscilloscopes are exceptional and very uncommon. The vast majority of analog oscilloscopes ever produced required a repetitive waveform to display a static image. Either that or a Polaroid camera attachment to capture a one-shot. Ask anyone who didthatback in the day if they'd rather have a modern real time scope with advanced triggering capabilities instead.QuoteNote again my carefully chosen wording: "If youwant to use your scopeto view or analyze a serial data stream, you'll need a real time scope."I did not suggest this is the only or best tool for the job, but if it is the tool that you have at hand, then it can be the right tool.QuoteAppropriate tools these daysincludescopes that sample fast enough to be useful in much broader usage scenarios than the limited scopes of yesteryear.The budget for a "spectrum analyzer with very good phase noise characteristics" is well beyond most hobbyists, especially those participating in a Beginners forum. A modulation domain analyzer is another special tool which does one thing very very well. The rest of the time it is just an expensive shelf queen. A fancy high speed logic analyzer would be great to have, but again it is expensive and takes up a pile of space. The average Beginner who is considering the likes of a low end Rigol scope probably doesn't need or want such things. One carefully chosen tool in the hands of someone who understands it capabilitiesand limitationscan cover a broad set of measurement tasks. Maybe you lost my point about the limitations of sampling scopes compared to real time ones. Or maybe you just love your scope so much that it biases your opinion. I get that, really I do. But let's be pragmatic here. If a person has only one scope on the bench, they would be poorly served by a low speed, high bandwidth sampling scope, especially with all the affordable options in 2017.Oh, and I didn't say anything about oscillators.