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In concept, these are great tools but unfortunately, these aren't very usable. I've seen a lot of these in the past and the day an affordable useful one hits the market, I'll buy 2.

The scope goes to 2MHz, if you want to view an accurate picture of a square wave, you'll need minimum 10x the fundamental frequency of the wave. So, at best, with this scope, you'll be able to view a 200KHz clock signal. You can pick up an old used 10MHz scope for the same price or cheaper and while it will not look great, it will be more useful.

The function generator goes to 100KHz which is not bad but given that it's only an 8-bit DAC, I don't think your 100 KHz signal will be very pure unless it's filtered. Given the sampling rate of their scope device, I'm not convinced that they would be able to produce a 100Khz square wave either (if they could, they would advertise 1MHz sine waves in addition (remember the 10x thing?)

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I can't figure out what this fascination is with USB 1.1 storage scopes. A USB 2.0 device can run a single 8-bit channel to 40MHz continuous, no storage necessary. As for the 10x sampling rate requirement Azira posits, I've never seen anything beyond 5x quoted as the minimum to get a reasonable picture of a signal, yielding an 8MHz effective bandwidth.

Either way, a faster device would be perfect for my hobbyist needs, as long as it costs $200 or less. Getting a standalone scope for that price doesn't give the ability to do long-running analysis of the signal, whereas a computer can store signals for a pretty significant amount of time, and review them after the fact.

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actually iirc the scope is 20MS/s so that means you can get 2MHz square wave clock signal.

also, the term DSO just means you -can- buffer. it also streams, although obviously as triggered as your brain cant process more than 60 frames a second. i mean, if your sample rate is high, you could easily pass the triggered data on something as low as an rs232 port

or am i confused?

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I'm one of the designers of these instruments, so it might help for me to respond to some of these points.

The sampling rate is 20MSamples/sec. To get a useable waveform, you need to have about ten samples per cycle, so the scope is useable to 2MHz. That's where we set the analog bandwidth cutoff.

I agree with Azira on the required bandwidth issue.
If you have to measure the rise time of square waves above 200kHz, you'll need a faster scope. (You can compensate by correcting the measurement, but this gets old fast.) This instrument was designed for work at modest frequencies, which includes (some) power supplies, servo systems, mechanical devices and audio. Most op-amp circuits work in this frequency regime. My experience in teaching electrical engineering is that there are many applications with that kind of frequency requirement.

Incidentally, we have viewed video waveforms on this scope and you can see a lot of detail. The bandwidth of video is about 3.5MHz as I recollect, and there are a lot of pulse-like details in that waveform. So it's quite useful for viewing a waveform (if not making precision measurements) up to and even above 2MHz.

We love the older analog scopes and have a bunch of them. But it isn't easy to capture the waveform data or do any sort of analysis on the signal: the PC host approach is much better at that. And an analog scope is a lot less convenient to lug around. (This one fits in a pocket.) So analog scopes and USB scopes have different strengths.

Regarding the purity of the generator waveform: a DAC gives (roughly) a signal/noise ratio of about 6db per bit, or 48db with an 8 bit DAC. We scale the output waveform so it maintains that S/N over the entire output amplitude range and a spectral analysis confirms that. If you are doing distortion analysis of audio equipment, you would need a lower distortion source. There is lots of published information on constructing such a device.

On the other hand, this generator can produce an arbitrary waveform, which is generally not possible with low-cost low distortion generators.

Regarding Omega's points: the instruments are USB 1.1 and 2.0 compatable, with the internal transfer rate of data about 3Mbaud (serial). That's the rate after stripping out the USB overhead. Buffering does mean that the units will work with a slower host PC.

With reference to ladyada's question: We do not have direct streaming implemented on this scope, but it would be possible to do so. Some people refer to this as 'strip chart mode'. It's on our todo list. The sampling rate would be quite low (because of the USB and processor overhead), but it would be continuous without any gaps. In fact, the original version of this scope did use RS-232, and it was quite useable at 56kbaud. But USB has compelling advantages and the update rate is quite high, the display looks like an analog scope.

I can't give details, but we're not stopping with these instruments...

Regards - Peter

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