So which scope to buy - Page 1
Forum section: electronics / testgear

author: mrpackethead
author_rank: Super Contributor
timestamp: March 21, 2017, 08:27:02 am
content: i was all set to buy a new scope and i've been bombarded with options..The things i do,Most microprocessor based work, with signals up to about 50Mhz.. ( clocks and some data lines )..Switch mode power supplies.. Typically runnig at 200-1500kHzI'd like to be able to do ethernet eye diagrams ( 10 and 100Mbs ) for embedded stuff.

author: BravoV
author_rank: Super Contributor
timestamp: March 21, 2017, 08:30:49 am
content: All answers will be useless if you don't provide the budget.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 21, 2017, 08:31:28 am
content: Depends what you want to spend. You can never have too much scope.Probably worth waiting to see the new Siglent that Dave has, especially as it apparently has serial decode as standard.If your budget stretches to the R&S RTB2004 launch offer, and it's still available and you don't mind waiting a bit, that's a total no-brainer

author: tautech
author_rank: Super Contributor
timestamp: March 21, 2017, 08:34:32 am
content: And you need to even ask on this forum ?SDS2104X with all options, MSO etc NZ$2390 + GST and if you're quick you can have a test drive before I deliver it on Friday.

author: ebclr
author_rank: Super Contributor
timestamp: March 21, 2017, 08:39:40 am
content: This little cheap thing will be more useful than a scope , when using with microprocessorhttps://pt.aliexpress.com/item/USB-Logic-Analyser-24M-8CH-24MHz-For-FPGA-ARM/32704469620.html?spm=2114.02020208.3.10.1DR6lB&ws_ab_test=searchweb0_0,searchweb201602_2_10065_10068_433_434_10136_10137_10138_10060_10062_10141_10056_10140_10055_10054_301_10059_124_10099_10103_10102_10096_10052_10053_10050_10107_10142_10051_10106_10526_10529_10084_10083_10080_10082_10081_10110_10111_10112_10113_10114_10037_10517_10078_10079_10077_10073_10070_10122_10123_10124-10517,searchweb201603_3,afswitch_1,ppcSwitch_5_ppcChannel,single_sort_0_price_asc&btsid=cd3ede7a-d030-4aee-b798-75c8ad79b30d&algo_expid=8f235446-c4d0-4a15-8811-f4d6978773ec-1&algo_pvid=8f235446-c4d0-4a15-8811-f4d6978773ecBut if you want the scope , Rigol DZ1054Z and Keysight Edu can be a option, Tektronics MSO is a must have but for few people with deep pocket

author: mrpackethead
author_rank: Super Contributor
timestamp: March 21, 2017, 08:52:04 am
content: Quote from: tautech on March 21, 2017, 08:34:32 amSorry not touching a siglent, i dont' like the way that you continously spam the forum.

author: mrpackethead
author_rank: Super Contributor
timestamp: March 21, 2017, 08:53:53 am
content: Quote from: BravoV on March 21, 2017, 08:30:49 amCan spend up to USD$7500, but i dont' wnat to spend all of that if i dont' need to. The ethernet eye diagrams are probalby the thing that pushes the spec requirement out.I dont' need serial protocol decodes, i have logic analysers that do an excellent job of that already.

author: mrpackethead
author_rank: Super Contributor
timestamp: March 21, 2017, 08:55:35 am
content: Untill you'r trying to see why somethign is'tn working as expected.. Scope and Logic analyser are good for too differnet jobs.Quote from: ebclr on March 21, 2017, 08:39:40 am

author: tggzzz
author_rank: Super Contributor
timestamp: March 21, 2017, 08:57:53 am
content: Quote from: mrpackethead on March 21, 2017, 08:27:02 amBe aware the bandwidth required depends on the transition time, not on the baud rate - and certainly not on the bit rate! Even for 40yo TTL, 100MHz is barely adequate, and modern jellybean logic signals have transition times much shorter than 1ns.

author: tautech
author_rank: Super Contributor
timestamp: March 21, 2017, 08:59:00 am
content: Quote from: mrpackethead on March 21, 2017, 08:52:04 amOK right then, not even if the packethead Trigger is included free.

author: tautech
author_rank: Super Contributor
timestamp: March 21, 2017, 09:02:57 am
content: Quote from: tggzzz on March 21, 2017, 08:57:53 amOne of my customers can do eye diagrams with a SDS1102CML from CD head read signals, not real brilliant but well enough that he was happy to use it to replace a 100 MHz Philips CRO.

author: mrpackethead
author_rank: Super Contributor
timestamp: March 21, 2017, 09:09:33 am
content: Absolutely, i have a 100Mhz Scope on teh bench right now and its just not fast enough to accurately show/meaure the rise time.. At a minimum i think i need 200Mhz, and ideally faster.Ethernet signals are 125Mhz, the book of words i have suggests you need 1Ghz to sensibly see that.Quote from: tggzzz on March 21, 2017, 08:57:53 am

author: mrpackethead
author_rank: Super Contributor
timestamp: March 21, 2017, 09:17:10 am
content: Quote from: tautech on March 21, 2017, 08:59:00 amnot even. A 100Mhz scope won't be fast enough for me.. and the packethead trigger would have to be minus money. Ie you'd have to pay me to take it off you.

author: tggzzz
author_rank: Super Contributor
timestamp: March 21, 2017, 10:17:12 am
content: Quote from: mrpackethead on March 21, 2017, 09:09:33 amThat "5*clock frequency" concept is basically false. It stems from considering the Fourier series of a square wave, and that if you eyeball up to and including the 5th harmonic, then itlooks likeareasonablysquare wave. Of course a circuit doesn't give a tinker's cuss about what the waveform "looks like". Consider a 1Hz TTL square wave; does it make any sense to use a 5Hz high pass filter with the signal!What you need to do is look at the frequency spectrum of the transmitted signal. For modern comms systems that has to beverywell specified and controlled, in order to maximise the channel's bit rate while minimising crosstalk and interference.Find the spectrum by either looking at the standards, or simulating of a waveform and doing an FFT. Find out the required bandwidth by simulating subtly faulty signals, then comparing the spectrum with an ideal signal.If you can't do that, then if the scope has a gaussian input frequency response (which isn't necessary and can be suboptimal) calculate BW=0.35/tr. That corresponds to 1ns<=>340MHz.But ignore the bit rate and baud rate and clock frequency; they are all irrelevant.Quote

author: nctnico
author_rank: Super Contributor
timestamp: March 21, 2017, 11:25:08 am
content: Quote from: mrpackethead on March 21, 2017, 08:27:02 amWhy would you want to do ethernet eye diagrams? There is no use for stuff like that unless you are designing ethernet PHYs. If you are worried about impedance then a network analyser is a much more usefull tool. Also the 100Mbit ethernet signals have frequencies up to 125MHz so a 500MHz oscilloscope should be enough. Keep in mind that the frequency content at 125MHz is already attenuated by 25dB so that only leaves a few ADC counts to display this content on an oscilloscope.

author: irakandjii
author_rank: Regular Contributor
timestamp: March 21, 2017, 01:42:53 pm
content: With a budget ceiling of $7500.00 I don't think this is a technical discussion.You would be better served by a cost / needs analysis focusing on your expected needs defined by a performance envelope for your DUT's.For example, if your MicroProcessors are 16 Mhz, (I use 180 Mhz Teensy, so I would use 180 Mhz for example)Extreme case probing clk line 16 MhzThen the very worst case ceiling on pins is is 8 Mhz on a pin, 1 clk HIGH, 1 clk LOW Generally overheads make this unreachable.List the rest of your circuit elements here.Capture the worst cases and select the highest one and you have your basic bandwidth. Determine the Nyquist / oversample factor you want. Usually 5X to 10X, some folks use 3X it depends on your sensitivity to accuracy / aliasing.Envelope = basic bandwidth X oversample Factor.Final Sample rate Envelope = Envelope X future proof factor ( I use 2, to account for a 360 Mhz Teensy within life of scope), but you pick the number you want)How often will you hit your envelope / sample rate? % of time, 75%, 50% of envelope etc ( design the table to meet your needs )How important is it to you (or your product) that you execute tests at the edges of the envelope? How much are you prepared to pay for the rare cases at the edge?(Example: My worst case final envelope would be 180 X 5 X 2 = 1.8 Gs/sec)Observations1) Anything above 360 MHz is wasted.2) Anything above 1.8 Gs/ sec is not worth paying for, but might be nice to have (note this implies a 70-100 Mhz scope).3) In my case, the highest expected "need" would be a decode on a 100 Mhz SPI bus. But, this would be very rare << 1%I constructed a table and found the following worst cases:Bit Bang (180 Mhz) - 0.9 Gs/sec per channel (highly unlikely to implement)SPI (100 Mhz) - 0.5 Gs/sec across 4 channels = 2 Gs/s totalI2C (5 Mb/s) - 0.025 Gs/sec across 2 channels = 0.5 Gs/s totalUART (.4608 Mb/s) - Not significantCan Bus (1 Mb/s) - Not significantNext features:Decodes = MandatoryNumber of channels = 4 - I want 4 so I can decode 4 wire SPI and 4 wire proprietary bussesAWG = Yes , I just want it. No real justification except conserve desk space which is a premium for meTouch Screen = nice to haveMSO = Yes, most of my work is digitalMemory = This ended up being a HUGE factor, more belowI/O (LAN USB etc) = Nice to haveBig Screen = Important, I am getting old.. eyes getting worse.Trigger Functions = Important but mid priorityMath Functions = Not sure, but don't want to ignore so yesMasking = Not importantAbility to do Bode Plots = nice to haveFFT = Low priorityOther.So my dream scope would have ~350 Mhz and a sample rate of 2 Gs or better and the features aboveBUT a review of scope pricing placed a market value of > $4000 (US) and closer to $7k for a full featured scope, most of these came with large & segmented memories. BUT my budget was not $7.5k, it was closer to $1.2-1.5 k so I had to park the dream and cost optimize.I looked at how often I would need things and what was most important to me, serial decode for signals in the 25 Mhz band became the most significant use case. (Note: I took a lot of effort and research to get to this point, but oddly the framework was similar to your stated needs)At this price point 1.2k -1.5k, memory architectureblows upas a very significant issue in terms of the capability / approach for long decodes.I won't get into the details herebut to meet myspecific needsthe best compromise was either a used Keysight 3000 (I could not find one anywhere near my price point) or a 100 MHz Picoscope 3405D. Basically the memory architecture of all the other 4 channel MSO scopes in my price range prevented me from doing what I wanted to do.AND Then I got lucky, I am almost never lucky! The introduction deal came for the R&S RTB2004 .. a little over my price point by $600 BUT it is very close to the "dream" spec. The rest is history.

author: tggzzz
author_rank: Super Contributor
timestamp: March 21, 2017, 01:52:20 pm
content: Quote from: irakandjii on March 21, 2017, 01:42:53 pmThat is something engineers always doAn engineer is someone who can do for $1 what any fool can do for $10.The key is thought, understanding and imagination. But you can buy equipment. (See my .sig)

author: macboy
author_rank: Super Contributor
timestamp: March 21, 2017, 02:11:10 pm
content: Quote from: mrpackethead on March 21, 2017, 09:09:33 amCat 5 (not 5e) cable has a specified bandwidth around 250 MHz IIRC. Rise time is far more important than "bandwidth". Technically, the observed rise time is the root-sum-of-squares of the signal rise time, the scope rise time, and probe rise time. So if you want the scope to show you accurate eye diagrams, you need the scope (and probes) to be much faster rise time than the signal. If it is only 3x faster, then it will have over 10% impact on the measurement. At 10x faster, it's just 1%.I see that the Rohde & Schwarz RTB2004 Launch Edition Promo which includes all optional upgrades free, is a tremendous deal. 300 MHz, 4 ch, 16-ch logic, waveform generator, etc. But 300 MHz might not be enough.I spotted a LeCroy J-250 on ebay recently for around $1.5k USD. This is a "jitter analyser" which really just means a scope (WavePro 950 in this case) with the jitter measurement package installed by default. This one is a 4ch, 1 GHz, 16 GS/s, 16 Mpt model. 1 GHz is fast enough for your eye diagrams. These are nice scopes, and the jitter measurement and visualization capabilities are really quite good, but the waveforms/second are a little low compared to the norm these days. And don't forget about probes.

author: alm
author_rank: Super Contributor
timestamp: March 21, 2017, 02:56:06 pm
content: Quote from: mikeselectricstuff on March 21, 2017, 08:31:28 amStill suggesting towait, Mike?Quote from: macboy on March 21, 2017, 02:11:10 pmI second the comment about probes. Be sure to consider what kind of probes you need. Both for budget and for compatibility. An active probe designed by Keysight will often not work with other brands' scopes without modification or adapters.If you are measuring very fast risetime signals, then it may turn out that you need low-Z probes or active (differential) probes. Depending on if the SMPS is DC-DC or off-line, you may need high-voltage differential probes. Current probes from DC to MHz can also be useful for SMPS designs.

author: bson
author_rank: Unknown
timestamp: March 22, 2017, 12:10:51 am
content: Quote from: irakandjii on March 21, 2017, 01:42:53 pmI think you fall exactly in the same target market I do - embedded systems design. For this, 500MHz, inexpensive active probes, MSO with a pod, and competent serial and parallel decodes (including triggering on digital patterns and bus writes to specific devices, and so) - is just the cat's pajamas. This is very different from power designs, or RF designs, or telco designs, and so on.I also have a Saleae Logic Pro 16 for deep captures. But I generally run it in parallel with a scope so help me determine what to look for (time wise). The ext out on the scope can be hooked to one of the lines on the USB probe; this way the scope can trigger/set a search condition for the Logic Pro 16. (And the scope has much better triggering, including mask testing, runt detection, etc.)QuoteThis is often how it works out - there are so many competent options in this market segment that the best one is simply the one you find a deal on. (I absolutely love my LeCroy WaveSurfer 3054 which I bought used simply because the right deal appeared in front of me.)

author: ElectronicCat
author_rank: Regular Contributor
timestamp: March 22, 2017, 12:28:37 am
content: Quote from: ebclr on March 21, 2017, 08:39:40 amHijacking this thread slightly, but are these cheap logic analysers any good? I was looking at a DS1054Z with the serial decode option, but then came across these cheap logic analysers. Seems too cheap to be any good, but then again I suppose they only have to record 1s and 0s.

author: bson
author_rank: Unknown
timestamp: March 22, 2017, 12:55:22 am
content: Quote from: ElectronicCat on March 22, 2017, 12:28:37 amBut what is a 1 and what is a 0? Can you define custom logic levels? With hysteresis? Can they operate differentially, say for LVDS? If so what's the CMRR? Can it tell you when something is NOT a valid logic level? What's the capacitive load on the circuit being probed?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 22, 2017, 01:37:15 am
content: The R&S has some nice intensity- colouring modes which may be good for eye diagrams. Can also invert intensity so less frequent events look brighter.

author: ebclr
author_rank: Super Contributor
timestamp: March 22, 2017, 04:17:11 am
content: This logic analyzer to a great job, make sure are based on cypress Fx2.This 5 USD units are a copycat of thehttps://www.saleae.com/yo can get the real thing for 50 times more expensive, Same things one guy developed and want a huge profit to supposed cover, development and engineering efforts, the other is a pirated unit, and sell for cents profit, since no intellectual people isenvolved, It's up to you decide from where to buy, Both work the same

author: mrpackethead
author_rank: Super Contributor
timestamp: March 22, 2017, 07:08:08 am
content: i have genine Salae. Its great. And i dont' mind paying for someone elses effort to develop it. Just like i ask my customers to pay for my stuff.

author: mrpackethead
author_rank: Super Contributor
timestamp: March 22, 2017, 07:11:34 am
content: I've short listed the RS2004 and the Keysight 3000. I can have 2 2004's for the price of one 3000, but the 3000 is upgradable ( and potentially hackable ) to 1GHz...

author: BravoV
author_rank: Super Contributor
timestamp: March 22, 2017, 07:22:41 am
content: Quote from: mrpackethead on March 21, 2017, 08:53:53 amI'm a noob, pardon for this question, say you got your scope that fits in your need and its fully capable to display the eye diagrams of ethernet signal as you wanted.What kind of potential problems (just name the common ones), once you have a perfect eye diagram displayed at your scope ? And the potential fix for it ?

author: mrpackethead
author_rank: Super Contributor
timestamp: March 22, 2017, 07:58:33 am
content: Quote from: BravoV on March 22, 2017, 07:22:41 amSimplistics, you can use it to determine the 'quality' of a repeatitive serial data stream.

author: tggzzz
author_rank: Super Contributor
timestamp: March 22, 2017, 09:11:26 am
content: Quote from: BravoV on March 22, 2017, 07:22:41 amhttps://www.google.co.uk/search?q=eye+diagram+techniquesThe wackypedia article isn't very helpful, but the next two are. In general look at manufacturer's application notes.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 22, 2017, 11:17:49 am
content: Quote from: mrpackethead on March 22, 2017, 07:11:34 amMSOX3000(T) vs. RTB2004 is not clear cut - there are significant plus and minus points on both sides so you'll need to look at both in detail based on your requirements.

author: mrpackethead
author_rank: Super Contributor
timestamp: March 22, 2017, 06:56:27 pm
content: Quote from: mikeselectricstuff on March 22, 2017, 11:17:49 amIn deed its not. It might even be a case of buying both... The RTB2004 would be a significant upgrade to the Rigol that is on the cal/repair desk. the extra capabilitys would be handy. Its almost a decvision that doe'snt need to much mor ethinking.

author: alm
author_rank: Super Contributor
timestamp: March 23, 2017, 12:28:10 pm
content: Depending on where you live and the R&S/Keysight presence there, you may be able to get a loaner so you can try them side by side for your specific applications.