So, I'm planning to add an oscilloscope to my arsenal. As I'm pretty much a newbie in this field of electronics, and only gonna use it for relatively simple tasks, I guess I won't need anything special. I've been looking into a few cheap USB oscilloscopes on different Hongkong sites, and this is the one that seems to fit my needs best, at least on the paper: http://www.dealextreme.com/p/usb-oscilloscope-and-logic-analyzer-93518 From the comments, it looks like it's an USBee knockoff, but that's no problem in my opinion. And it's really cheap, so I won't cry blood if it turns out to be complete crap after all. Of course I realize that the old device "you get what you pay for" applies here too, and that it can't be compared with the real deal, but hopefully it works well enough to satisfy my needs. However, before I make the decision to order, I wanted to check if you advanced users have any words on it? Do you believe it's even worth the $42 they ask?
3 MHz bandwidth?!! That's dire! You could actually get a second hand proper 20 MHz scope off eBay for a similar price. Depends what you're going to be using it for, really. 20 MHz is OK for basic stuff. I assume they actually meant 16 MHz bandwidth. You'd usually look to have a scope with a bandwidth of about 5x the frequency signal you're looking to measure... so that makes sense. The answer really is what do you want to use it for? And then you'll answer your own question by comparing its capabilities with your requirements. USB scopes aren't necessarily bad - some are quite good. Those are cheap for a reason, though.
No. Do not the cheap ones. They are shit. Mine was a complete waste of my time. I spent 3 hours trying to get a reading, and when I did, it was wrong. I paid $30 for it. If you're going to get a scope and use it properly, get a good one.
I doubt that thing is worth the $42, however if it is just something you are going to use once or twice it might be worth it. You can a Rigol DS1052E for around $300 which would be a great starter scope.
Yeah, I came to the same conclusion - since it's a digital scope, the sampling frequency could be regarded as an equivalent to the bandwidth of an analog scope, so to say. I'm gonna use it for a multitude of tasks I guess. It's as always with this kind of tools, you don't really know everything on beforehand, but once you get it you'll find uses for it, and soon you wonder how you could live without it. The only specific usage I know right now is analyzing some video signals, and a scope with those specs should be (barely) sufficient for that, at least if I've understood everything right. As I mentioned I'm not an all that advanced user, mostly it's gonna be a complement to the old trusty multimeter --- Anyways, what I mostly wondered is if those cheap scopes even works as advertised. From your answers, it looks like they don't, and are not worth the price they ask for them. I'll pass this one, and see if I can get a good deal on an used proper scope instead, it's not like I'm in a hurry to get one. Thanks for your input, guys!
Sampling rate and bandwidth are not the same thing and you really can't just say 5-10x oversampling is enough headroom without taking into account the analog frontend's bandwidth or the anti-aliasing filter. To accurately sample an waveform you need an anti-aliasing filter to remove all frequency components above Fsamp/2 to below the precision of your ADC. Since it's hard to design steep filters oversampling (raising Fsamp/2) is used in combination with a more modest filter to achieve your desired bandwidth. I wouldn't be surprised if that scope's usable bandwidth was under 3 MHz, nor would I be surprised if the entire implementation was broken due to omitting any possible component as they often do in China or just shoddy DSP work in general. Since you want to do video work, assuming this is SD video, you probably want 10 MHz bandwidth. At minimum this would be a 20 MSamp/s DSO, with an ideal filter, but more realistically 100 MS/s with a high quality filter. Once you get into higher sampling frequencies such as 100 MS/s then you MUST get ridiculously overpriced professional equipment because you're dealing with transmission lines and low cost products and amateur projects are not engineered to that quality. When you get a "nominal" $1500 scope from Tek, you're actually getting a 1 GS/s+ ADC, huge order analog filters and the frontend will have controlled impedance. Unfortunately it is how it is I'm in the same boat and I'll probably have to settle for an analog scope older than me with my budget.
