Low cost oscilloscope advice for start - Page 1
Forum section: electronics / beginners

author: Yaro
author_rank: Contributor
timestamp: January 17, 2015, 11:06:51 am
content: Hi all,I see on the web different low cost oscilloscope like hantek 6022, DSO201 and much more. But I never had an oscilloscope and I want to ask an advice from someone that have tryed them or know them.My main use of them is to analyze digital signals with a freq. about 40Mhz. I know this is too fast for a low cost oscilloscope, but what I ask is something with a price below 100dollars with the best performance I can get at this price.Thank you.

author: devanno
author_rank: Regular Contributor
timestamp: January 17, 2015, 07:05:04 pm
content: Quote from: Yaro on January 17, 2015, 11:06:51 amYou're analyzing digital signals, why not go for a logic analyzer? The problem here is your price point vs. your frequency. Used analog oscilloscopes that would handle that range with acceptable results -might- be found at places like eBay. There is a classic "rule of 5s" that says that you want your "system" to be 5x the capability of the highest waveform you might want to measure. This would mean you are looking for a 200MHz oscilloscope.Others.. I'm not sure if this "rule of 5s" is still considered valid, so if I'm wrong here, please correct me.

author: ralphd
author_rank: Frequent Contributor
timestamp: January 17, 2015, 07:12:23 pm
content: I agree; you're not going to find a new 40Mhz scope for $100. As you have probably read elsewhere on eevblog, the best/cheapest 40Mhz scope you can get is the DS1054Z for US$400.For a cheap logic analyzer, this might do the trick:http://www.aliexpress.com/item/1pcs-lot-Free-shipping-New-Arrival-Saleae-Logic16-saleae16-USB-Logic-Analyzer-100M-16CH-best-quality/667671473.html

author: Yaro
author_rank: Contributor
timestamp: January 18, 2015, 09:54:36 am
content: Thank you, this is what I need.Also, if I want to measure noise on my circuit lines that are below 100Khz any oscilloscope that have a bw with at least 1Mhz is good?On hantek 6022 I've read that the programm work bad. And DSO201 have the same prices as Hantek but have just 1Mhz of bw.Now, suppose if i what to measure 3-5Ghz noises, how it's possibile? There's any oscilloscope that can do this?

author: tggzzz
author_rank: Super Contributor
timestamp: January 18, 2015, 12:26:47 pm
content: Quote from: devanno on January 17, 2015, 07:05:04 pmA 40Mb/s signal "is" a 20MHz square wave, and the rule of thumb would imply a 100MHz scope.More accurately, the period is irrelevant andonly the risetime is relevant. BW = 0.35/risetime.My bias is that, since nothing is truly digital until you are dealing with individual electrons/photons, you need to use a scope to check the signal integrity. I.E. clean transitions, correct levels. Once you have good signal integrity and and therefore know the digital signals are reliable, you are working in the digital domain and should use digital tools. Yes, there are exceptions, but those aren't relevant here.IIRC the fastest scope is160GHz160GS/s, which would easily see a 5GHz signal. But if you could afford it you wouldn't be reading this forum.If you are looking at "GHz noises", then you are probably more interested in a power meter and/or a spectrum analyser. Understanding what you want to measureand whyis the key to picking the right tool for the job.

author: Yago
author_rank: Frequent Contributor
timestamp: January 18, 2015, 12:41:14 pm
content: Quote from: tggzzz on January 18, 2015, 12:26:47 pmThought that was the other way round, as in;40Mb/s is an 80Mhz square wave?Note this a question, NOT a statement!Welcome to the OP, not a bad name you have there!

author: Howardlong
author_rank: Super Contributor
timestamp: January 18, 2015, 01:15:55 pm
content: Quote from: Yago on January 18, 2015, 12:41:14 pm40Mbps uncoded maximum frequency is indeed 20MHz.Edit: think what a string of alternating 1s ans 0s generates...

author: Yago
author_rank: Frequent Contributor
timestamp: January 18, 2015, 01:28:42 pm
content: Cheers Howard, I get it now, I was thinking that there would need to be separation between the bits, but of course not, it is timed!

author: Rick Law
author_rank: Super Contributor
timestamp: January 18, 2015, 05:36:07 pm
content: I use a Hantek6022. I can say for sure you have no chance with 40MHz. Well, mathematics already said no, but I tried it in practice just for the fun of it.I recovered a 40MHz oscillator from a PCI (SCSI I think) board. The Hantek isn't showing anything close to looking square. It samples at 20MHz, that means it gets only one data point (approx) only every other cycle of a 40HMz wave.You need at least a few points inside each cycle of a wave to see something close to the original wave form. The 5X is really min. 4X will give you an very very rough idea.

author: tggzzz
author_rank: Super Contributor
timestamp: January 18, 2015, 06:08:15 pm
content: Quote from: Rick Law on January 18, 2015, 05:36:07 pmDon't confuse sampling rate and bandwidth;they are completely and utterly independent in scopes.Some scopes have 1GS/s and a 100MHz bandwidth. Other scopes (that I have used) have a 1GHz bandwidth and 40Ms/s (i.e. 25ns sampling period). Both are useful.

author: devanno
author_rank: Regular Contributor
timestamp: January 18, 2015, 06:47:26 pm
content: Quote from: tggzzz on January 18, 2015, 12:26:47 pmAh, right... wasn't thinking clocking speed on the square wave. :-) Clearly, I need more coffee!

author: tggzzz
author_rank: Super Contributor
timestamp: January 18, 2015, 07:24:51 pm
content: Quote from: devanno on January 18, 2015, 06:47:26 pmThe OP quoted MHz, for which you are right. I mutated his point, possibly irrelevantly, in MS/s since many people get confused.Either way, for this discussion it is the risetime of a digital signal that is important, not its frequency/period.

author: Rick Law
author_rank: Super Contributor
timestamp: January 18, 2015, 11:04:54 pm
content: Quote from: tggzzz on January 18, 2015, 06:08:15 pmI sure did confused the two when I wrote that post. I was watching a Zombie movie as I browse, and acted I like one myself.Hantek 6022BE samples at 48M sample/second up to about 1000 datapoints. Not 20MHz.(darn keyset.. took me three reboots to get this post right...)

author: Yaro
author_rank: Contributor
timestamp: January 19, 2015, 08:55:15 am
content: Quote from: Rick Law on January 18, 2015, 05:36:07 pmWhat can you tell me about it's software? A lot of user says that is unusable and have very high delay, that's true?

author: Yaro
author_rank: Contributor
timestamp: January 19, 2015, 09:14:30 am
content: Quote from: ralphd on January 17, 2015, 07:12:23 pmI want to ask how this works. It waits signal input or it sample input 100M times? In other words, 100M means it can sample up to 100Mhz input freq.? Or how to correctly choose it?

author: Rick Law
author_rank: Super Contributor
timestamp: January 19, 2015, 08:26:36 pm
content: Quote from: Yaro on January 19, 2015, 08:55:15 amThe stock software is not so bad. It is lacking some features but is rather usable. There will be "blind time" with any DSO. I can't tell you what I can't see (if there is a delay and lost something, I don't see it and I wont know what is missing). But I found it very satisfactory for my use: at typically less than advertised 20MHz bandwidth.This is a low cost piece of equipment and you get what you paid for. For this one, a rather good deal but it is after all a low cost scope so some features (such as AC coupling) is simply not there.There is a long thread on this forum for this DSO. There, you will also find download for a better piece of software written by forum member RichardK. I use that PR18 version every now and again. PR18 has a lot more features including software-AC-coupling, but slower on my machine. I use PR18 mostly when I review captured wave form with its added features. But as said, it is slower on my machine so I normally use the stock software, and I can use Window's remote desktop to see the scope while I am upstairs in a different room.Go there and check it out. Along with review and RichardK's software, I also posted a lot of details about the scope's data capturing capabilities there. i.e. info on timeDivision vs samplesPerSecond vs sampleSize.https://www.eevblog.com/forum/testgear/hantek-6022be-20mhz-usb-dso/