Oscilloscope spec question - Page 1
Forum section: electronics / beginners

author: ploughna
author_rank: Newbie
timestamp: September 21, 2018, 01:46:29 pm
content: I'm planning to buy a lowish cost scope for hobby use - both general electronics (microcontrollers, analog ampliers and the like, sensors, etc) and some ham radio related projects. May invest in a spectrum analyser as a later date for my radio projects, but view this as more a luxury than necessity.Question relates to scope specs. Am I better off with a lower bandwidth scope with higher sampling rate than high bandwidth lower sampling for the same money?Eg 100MHz 2Gsa/s or 200MHz 1Gsa/s?And if 1Gsa/s is enough for my needs, does 200MHz 1Gsa/s even make sense - seems like very poor resolution at 200MHz. I could get 100MHz 1Gsa/s for much less money or increase the number of channels for the same moneyAny thoughts on this gratefully appreciated. I'm ok to spend a bit more money but only if I'll get value from it. Budget is $500 ideally, $750 at a stretch, and would need some good convinced to go to an absolute max of $1000RegardsPaul

author: rstofer
author_rank: Super Contributor
timestamp: September 21, 2018, 02:01:44 pm
content: The magic number to remember is 2.5.You will find that most scopes have a max sample rate of around 2.5 times the maximum bandwidth.Take the Rigol DS1054Z - 4 channels, 100 MHz, 1 GHz sample rate. Multiply 4 ch * 100 MHz/ch * 2.5 samples/Hz and you get the magic number 1 GHz. This is related to the 2x sample rate requirement given by Shannon and Nyquist - sampling theory.The question is how many channels are active. The DS1054Z is smart enough to use a faster sampling rate if fewer channels are enabled. As are most scopes...There are two major players in the entry level scope arena: The Rigol DS1054Z at well under $400 which, when unlocked (details elsewhere) to 100 MHz, is a very capable 4 channel scope. Since you are planning to mess around with microcontrollers, I'm going to recommend 4 channels and the ability to decode SPI.The other is the newish Siglent SDS 1104X-E - a more recently released 4 channel 100 MHz scope. It's around $500 and, according to reviews, the user interface is much more responsive. Look for threads in the Test Equipment forum here on EEVblog.The Rigol has the advantage of being around for 3 or 4 years and has gone through several firmware revisions. The Siglent is newer and I'm not tracking firmware issues.For my money, I would probably buy the Siglent SDS1204X-E to get 4 channels and 200 MHz. But it's around $750 and I'm not quite willing to spend that much right now. I do have the Rigol.

author: ploughna
author_rank: Newbie
timestamp: September 21, 2018, 02:19:21 pm
content: That's very helpful - thank you.So with the Siglent SDS1204X-E, 2 channels up to 200MHz and 4 channels up to 100MHz preserve the 2.5x rule of thumb formula.

author: Old Printer
author_rank: Frequent Contributor
timestamp: September 21, 2018, 05:13:13 pm
content: Quote from: rstofer on September 21, 2018, 02:01:44 pmI think the Siglent is hackable from 100 to 200 Mhz, maybe not as easy as the Rigol is from 50 to 100. If this is true, and the OP is comfortable with the hack, that puts the Siglent at $500. Worth looking into.

author: tggzzz
author_rank: Super Contributor
timestamp: September 21, 2018, 05:32:01 pm
content: It depends on what you want to use the scope for.No amount of fast sampling can make up for a lack of bandwidth. In that sense the samples/second is mere marketing speak.A prime use of a scope is to verify digital signal integrity; for that purpose a high bandwidth is necessary, but the sampling rate can be arbitrarily low since the signals are repetitive. (My fastest scope has a sampling rate << 1/1000 of its bandwidth. It observes signals with a risetime around 140ps)If you need to capture non-repetitive analogue signals, then the sampling rate becomes important.If you need to capture non-repetitive digital signals, use a cheap logic analyser.

author: MrW0lf
author_rank: Frequent Contributor
timestamp: September 21, 2018, 08:10:39 pm
content: Quote from: ploughna on September 21, 2018, 02:19:21 pmAFAIK Siglent has 2 ADCs = 4ch up to 200MHz.

author: rstofer
author_rank: Super Contributor
timestamp: September 21, 2018, 08:35:34 pm
content: Quote from: Old Printer on September 21, 2018, 05:13:13 pmIt's my understanding that this is true. I haven't followed along since I already have the Rigol and a Tek 485 when I need 350 MHz bandwidth.

author: ploughna
author_rank: Newbie
timestamp: September 22, 2018, 09:12:36 pm
content: I've read a few threads related to that bandwidth hack but honestly it looks quite involved and maybe even risky (at least for me). It also wasn't clear to me that the hardware was truly the same and the only differences lay in the software.

author: tautech
author_rank: Super Contributor
timestamp: September 22, 2018, 09:25:30 pm
content: Quote from: ploughna on September 22, 2018, 09:12:36 pmWith modern equipment the model BW is commonly limited with SW code.

author: rstofer
author_rank: Super Contributor
timestamp: September 22, 2018, 09:36:36 pm
content: The Siglent hack seems more involved than the Rigol approach.First, I have to replace the firmware with a version with a known root password.Second, I have to modify the contents of a file using TelnetFinally, I have to upgrade the firmware to a new factory release.All of the above is my vague recollection of the process which is described elsewhere. The first step is where I get nervous. Who created the replacement firmware? Do they guarantee it won't brick my scope? Is their firmware known to work on the latest hardware release?This process is probably workable but it seems to me that it is a little more risky than for the Rigol. I'm not sure I'm willing to do it. It might be that the extra money for the 200 MHz vs 100 MHz BW just isn't that important. The only reason I would consider buying the Siglent is for the BW because my Rigol works fine.