Putting higher frequency through a scope - Page 1
Forum section: electronics / testgear

author: Siehbi
author_rank: Contributor
timestamp: April 19, 2014, 08:20:24 pm
content: Hey I was wondering about this question on an oscilloscope,Imagine you have an oscilloscope that has a 60MHz Bandwidth, I was wondering if you put 100+MHz through the probe leads (assuming that they are rated for that frequency) and into the scope what would happen?What if you go into the GHz range, would that do any effect?Also I would like to request what not to do with an oscilloscope.Maybe also some advice on the oscilloscope, Uni-t UTD2062C. I will be using this scope for general use and it will be my first scope.Thanks for your time,Nicholas

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 19, 2014, 08:27:18 pm
content: Those ratings are the upper limits of sensitivity. Beyond those frequencies, they just "ignore" the signals. They cannot sense that there is even anything there to see/hear. Of course, this happens gradually, it isn't a "brick wall". If you look at 61MHz with a 60MHz rated scope, it may read slightly lower than it should. And at 70 MHz, you can depend on what you see/measure not being accurate, etc, etc.PS: Please try to use better subject line. There are very few of these discussions that couldn't be named "I have a question." Not only doesn't it mean anything, but it doesn't even give us any clue what this is about?

author: 128er
author_rank: Regular Contributor
timestamp: April 19, 2014, 08:48:28 pm
content: Quote from: Richard Crowley on April 19, 2014, 08:27:18 pmAnd it makes it easier to find the right topics over the forumsearch.Quote from: Siehbi on April 19, 2014, 08:20:24 pmDont measure the mains. Until you are reeeaaaaallly know what you are doing. Or you have the right safety precautions.

author: Sebastian
author_rank: Regular Contributor
timestamp: April 19, 2014, 08:53:47 pm
content: The frequency spec of a scope is usually the 3dB bandwidth of the analog front end. 3dB is about 30% attenuation in case you don't know. So if you are going to measure a signal with the maximum frequency of the scope it shows only 70% the amplitude of the real signal. But a lot of scopes have their 3dB bandwidth a bit higher than the spec, so it's just the worst case. But if you want to measure a much higher frequency you won't be able to see anything because the signal that gets through to the ADC (in case of a digital scope) is lower in amplitude than a single step of the ADC.

author: electr_peter
author_rank: Unknown
timestamp: April 19, 2014, 08:57:14 pm
content: If multi GHz signal is fed to 60MHz oscilloscope, 3 effects happen:1) signal amplitude is significantly reduced (attenuated) - due to bandwitdth limitations of probes and oscilloscope input circuitry.2) Digital oscilloscope will undersample high frequency signal - weird effects could happen on the screen.3) scope would lose trigger - trigger circuitry is on par with oscilloscope bandwidth.Thus, scope would not show anything for higher frequencies.Quote from: Richard Crowley on April 19, 2014, 08:27:18 pm

author: Siehbi
author_rank: Contributor
timestamp: April 19, 2014, 09:01:52 pm
content: Ok I just changed the title to something different I hope it matches the topic. Thanks for all the replies. Can anyone give me suggestions on the scope that was mentioned in my first post?ThanksNicholas

author: pickle9000
author_rank: Super Contributor
timestamp: April 19, 2014, 09:26:47 pm
content: Persons dealing with higher frequency stuff will often "quick check" the input by simply putting a frequency counter on the signal to see if it is within range.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 19, 2014, 10:18:04 pm
content: For example, my 350MHz DSO can observe over 800MHz, but the amplitude is certainly wrong, and the frequency is harder to observe (though probably easier on a DSO, given the timebase is basically software).Having a good trigger is most important: if you see a blurry trace, you know there's something out there, but if you can't stabilize it, you won't be able to measure the frequency.Tim

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 19, 2014, 10:51:18 pm
content: Quote from: Siehbi on April 19, 2014, 09:01:52 pmIt is a much nicer piece of gear than many people have.It is not clear exactly what you are asking?Are you asking about whether to get one? Or do you already have one?Are you asking about safety? For yourself? For the instrument?Are you asking about how to use it?We can't read your mind at this distance. More specific questions will get you much better results in online forums like this.

author: David Hess
author_rank: Super Contributor
timestamp: April 19, 2014, 11:18:52 pm
content: Quote from: electr_peter on April 19, 2014, 08:57:14 pmHigh impedance oscilloscope inputs also have their safe overload specifications derated by frequency so the input could be damaged. Probes do as well.Oscilloscopes which use analog triggering often have good trigger response extending significantly above their rated bandwidth.

author: Siehbi
author_rank: Contributor
timestamp: April 20, 2014, 07:26:25 am
content: Quote from: Richard Crowley on April 19, 2014, 10:51:18 pmOkay I was originally asking about advice in general but now that you inspired me I would like to request information on safety of this scope, i.e. If I screw something up will it fail safely? Also looking at the specs I saw vertical sensitivity, will this interpret its maximum input voltage? Also what is its maximum input voltage? And will you recommend this to somebody that is looking for his first scope?This scope seems like the only option here locally at Malta, except a lower 20MHz scope... which there isn't that much of a difference on the price.Thanks to allNicholasP.S. The link to specs of the UTD2062C is:http://www.uni-trend.com/UTD2062C.htmlBTW Happy Easter to all

author: David Hess
author_rank: Super Contributor
timestamp: April 20, 2014, 07:53:52 am
content: Quote from: Siehbi on April 20, 2014, 07:26:25 amThe biggest danger is shorting something out via the probe ground leads. The signal connections are usually not a problem.QuoteOn a properly designed oscilloscope, the maximum input before damage is unrelated to the vertical sensitivity setting.QuoteIt is usually 300 volts or higher. If you use a passive attenuating probe, then it will be even higher and usually limited by only the probe.QuoteI usually recommend starting with the least expensive option simply to get a better idea what one needs.I would not recommend the UTD2062C simply because so little documentation is available. I have no idea what its overload capability is.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 20, 2014, 10:42:27 am
content: In the Beginners Sectiliston of this board is a listing (right at the top) for: "Oscilloscope Training Class (Long)"Have you viewed that yet? Did you understand the topics? Recommended.https://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/Most forums like this have well organized sections so you can look through them.And they have a Search feature so you can look up your question to see if it has been asked before.While most of us are happy to answer questions, it becomes redundant for people to come hereand ask the same questions over and over again. So they have certain topics that many peopleask, which are permanently at the top of the lists. That is called making them "sticky".They are the ones with a darker background which are at the top of each list.I suspect that the answers to to most of your questions (and probable most of thequestions you haven't discovered yet) have already been asked and answered.And they are just waiting there for you to read. You don't have to wait for us to respond.https://www.eevblog.com/forum/beginners/newbies-please-read-before-posting-24542/

author: Siehbi
author_rank: Contributor
timestamp: April 20, 2014, 10:59:24 am
content: So from what I can understand is that your only problem is that there isn't enough information listed on the website. Otherwise from the specs listed what do you think?Nicholas

author: David Hess
author_rank: Super Contributor
timestamp: April 20, 2014, 04:02:01 pm
content: Quote from: Siehbi on April 20, 2014, 10:59:24 amYou have to cut the coat to fit the cloth. If that is the only oscilloscope available to you then you may need to make do.Personally I find the lack of available documentation to be a warning that the product is questionable but one specific thing that stands out to me is the low resolution of the LCD display. It seems more like a toy than a measurement instrument.

author: Siehbi
author_rank: Contributor
timestamp: April 20, 2014, 05:28:05 pm
content: Okay agreed but I don't think that, that will bother me a lot. Does anyone know any new oscilloscope shops in Malta?Also the scope that I was looking at before was the Rigol DS1052E which has the same resolutions but better sampling rate... The Uni-t has a higher bandwidth. How bad does a 500MS/s look like?Nicholas

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 20, 2014, 05:57:54 pm
content: As you suggest, restricting yourself to what you can find "off the shelf" in Malta seems extraordinarily limiting. Frankly, I am surprised that you could buy any kind of test gear at a storefront on such a tiny island.If is impossible for us to express any kind of opinion on what specifications you should look at, because you have told us nothing about what you are doing or why you even need an oscilloscope?

author: Siehbi
author_rank: Contributor
timestamp: April 20, 2014, 06:10:40 pm
content: Yes okay its kind my first time on a forum so still learning. Well i would like an oscilloscope for general use like trouble shooting stuff. I am getting an oscilloscope so that i can expand my knowledge on electronics.I was surprised too... right now I am looking for oscilloscope withing the €300 - €400 price range.If you need to know anything else just ask and I will tell you.Nicholas

author: David Hess
author_rank: Super Contributor
timestamp: April 20, 2014, 07:00:43 pm
content: Quote from: Siehbi on April 20, 2014, 05:28:05 pmThe maximum supported sample rate is not going to be the limiting factor in what you use the oscilloscope for so it is not a specification that I would assign high value to.The display quality is more important.

author: Richard Crowley
author_rank: Super Contributor
timestamp: April 20, 2014, 07:13:44 pm
content: I agree with Mr. Hess that the screen resolution seems sub-par.I came across a very glowing review and 4 pages of positive comments about a DMM from the same manufacturer. Apparetly halfway decent stuff at a very good price. At least for that model. We don't know whether we can extrapolate that experience to their oscilloscope products.https://www.eevblog.com/forum/testgear/review-uni-t-ut136b-tired-of-the-multimeter-snobs-a-very-nice-budget-meter!/

author: Siehbi
author_rank: Contributor
timestamp: April 20, 2014, 07:30:42 pm
content: Well thanks for all you help i will probably be getting this scope. If I hook up this scope to my PC and preview the Waveform over there will this be a possible solution to the screen resolution?

author: David Hess
author_rank: Super Contributor
timestamp: April 21, 2014, 02:11:12 am
content: Quote from: Siehbi on April 20, 2014, 07:30:42 pmIt might be but the lack of available documentation makes this unusually difficult to determine without direct evaluation.My personal experience is that PC test instrument interfaces are second best but sometimes useful for more complex data analysis. For general development and troubleshooting work, I prefer using test instruments directly.I am sure the oscilloscope will be useful but if you had an alternative like an older but working analog oscilloscope at a good price, I would recommend that instead.

author: Mark_O
author_rank: Frequent Contributor
timestamp: April 21, 2014, 05:36:20 am
content: Quote from: Siehbi on April 20, 2014, 07:30:42 pmProbably not. Even though the screen size on the PC software is 460x350, it likely just scales up the 320x240 pixels from the device screen. It's difficult to be sure though, because every aspect of the documentation on this is so bad, all one can do is guess. They don't showa single trace of any kindin their software manual. For someone who is "getting an oscilloscope so that i can expand my knowledge on electronics", this seems a pretty poor match. Also, the software doesn't draw things on-screen properly, with areas drawing outside their boxes, and highlights leaving areas undrawn. Very amateurish. This is for software Version 8.8, that they worked on for 5 years (2007-2012). And is almost certainly the last version they'll ever release.The performance specs on the unit are adequate, and in the same class as the Rigol 1052E you were also looking at. It's a model from about 7 years ago, and very old technology. But the published specs, even on the manufs own web site are like a "back of the napkin" list. Very unprofessional. So I downloaded their manual, expecting a User Guide for the scope. Instead, it was a manual on how to install and operate the software! If there's no User Manual with it (and there is none I could find on-line), that will make learning vastly more difficult than it would be with any other scope I've seen.With as horrible a job as they've done documenting their scope, what do you expect your experience will be if you have a post-purchase question? Or have a problem with it and need servicing? Their web resources really give me no confidence at all in their product.I'd agree with David's recommendation to find an older, working analog scope, if you can. That would be a lot more affordable. Something with a manual so you can learn how to operate it effectively. If you decide you really want a digital scope, I'd think the Rigol you mentioned would be a better choice, even if for no other reason than it's well documented and has a decent User Guide. Plus there are many who could answer questions on that device, while few are likely to have experience with the Uni-Trend.I really can't tell from your descriptions, but it sounds as if you don't have much electronics knowledge. ["How bad does a 500MS/s look like?" suggests almost none.] And are hoping if you just had a scope, you could somehow be able to troubleshoot problems, and fix things. But you will have to not only learn some electronics basics, but also figure out how to set up and use the scope too, and then interpret what you're seeing.

author: Siehbi
author_rank: Contributor
timestamp: April 21, 2014, 09:03:09 pm
content: Well you are starting to convince me that the Uni-t isn't that great oscilloscope that i was thinking of... Can anybody give me a recommendation on what cheap oscilloscope i can buy and if you are up to the job can you find me an online store which sell that oscilloscope and that ship to Malta with a good warranty and customer care. I dont really like analog oscilloscopes with the CRT screens, last time i was in front of one it irritated me a bit.Thanks

author: 128er
author_rank: Regular Contributor
timestamp: April 21, 2014, 09:38:45 pm
content: Quote from: Siehbi on April 21, 2014, 09:03:09 pmMaybe you had to turn the intensity down

author: Mark_O
author_rank: Frequent Contributor
timestamp: April 21, 2014, 10:28:58 pm
content: Quote from: Siehbi on April 21, 2014, 09:03:09 pmWell, the Rigol you were looking at is adequate, and about as cheap as you'll find, excluding used analog CRTs you don't like. Plenty of people here have them, to answer the inevitable questions as you get up to speed.QuoteWould you like a beverage and appetizers, while you wait?