oscilloscope

Thanks for the offer, John, I'm in Australia. I was not contemplating actually buying either of these at the moment, just doing some ground research about two affordable options at my local shoppe. jack

I have a few scopes I have bought, used from eBay and refurbished, including new electrolytic caps in the power supplies. I have an analog storage scope and a non storage Tektronix with roughly these specs that I am willing to sell for a lot less than $350, each. If you are in the U.S., and want more details, email me with an actual address, and we can talk.

This sounds like a very ordinary, low end, 2 channel analog=20 scope. It would have lots of uses for audio and other=20 analog signals, and also digital, except for the timing=20 details of digital edges. Even a small, slow microprocessor=20 would might react to things you would miss or see distorted=20 with only 20 MHz bandwidth. But still potentially very useful.

The only feature missing that you might find a need for, is=20 delayed sweep. when you are looking at digital sequences,=20 you sometimes need to examine a detail that is significantly=20 delayed from a trigger event. If you use a horizontal sweep=20 time long enough to get both the trigger event and the one=20 you want to see on the screen at the same time, the details=20 are too crowded together to make out anything useful.=20 Delayed sweep is 2 sweep generators. the first starts at=20 the trigger event, and acts as a programmable delay, that=20 triggers the second, which sweeps the trace. In effect, you=20 get a programmable delay between the trigger event and the=20 expanded trace of some period of time after it. But you=20 can, also alternately, see the whole time period, but with=20 the delay portion dimmed, and the delayed part brightened,=20 so you can set the delay.

I would say that these specs indicate an absolute bandwidth=20 of less than 100 kHz, which is poor for any use except low=20 frequency analog and audio stuff. Microprocessors can have=20 a lot happen in 5 microseconds (the time between samples).

This seems to be referring to 1 bit resolution (recording if=20 a signal is either above or below a threshold voltage,=20 somewhere between 0 and 5 volts. A logic state recorder,=20 not really an oscilloscope. But at least it is fast enough=20 to follow more of the range of microprocessor signals. This=20 sort of thing is normally called a logic analyzer, used to=20 capture the parallel processes of buses or other multi bit=20 processes.

Very handy as a signal source simulating the missing parts=20 of a system, when you are testing a part of a logic system

[...] You really need something like 40Mhz-50Mhz. Nothing worse than paying full whack for kit and then weeks later find you're hankering for more spec'. Myself, I'd buy second hand on ebay. [...]

Sounds like the work of a marketing specialist. Reads as marvellous but is basically useless. It's a data logger at 200kHz samples a second. As I'm feeling grumpy, I'll take the cynical path ... You need about 600 dots across a display to give a reasonably clear pic' (any display). So if you want on screen a single cycle of the waveform you're interested in, then it will need to be composed of 600 dots or samples. This tells you that the best the device can do is 200,000 samples per second / 600 samples on screen = 333 Hence the frequency response tops out at a heady 330Hz. Unit could be useful for monitoring clean mains waveforms or battery discharge curves.

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Posted via a free Usenet account from http://www.teranews.com

< snip very useful stuff >

Thanks muchly for that explanation, John, it has helped me a lot. jack

Thanks John. That second one is much as I suspected, but wasn't sure. I am suspicious when folk "namedrop". A clear jargonfree explanation shows they have nothing to hide. I think the second-hand route is the way to go. I just need a bit more study and research to know what to look for and to know when I have found it :) So far, I seem to have gleaned that a 60MHz analogue machine is going to give me the best bang for the buck. Digital, storage and other fancy bits are pretty much jam on the bread. Cheers, jack

A scope of any kind is going to show you things you just couldn't see any other way. Any "real" scope (not a USB logic analyzer) is going to let you see moving, repetitive signals that would otherwise be very hard to id. It's a quantum leap from a voltmeter for certain problems. Storage (which usually comes along with digital) is going to let you look at one-shot signals, logic bus transactions, long term averages, automatic measurements and more. It's a quantum leap from an analog scope[*] for certain problems. However, the prices are commensurate.

[*] And there are some things an analog scope is better for, too, but if I were trapped on a desert island doing mixed-signal design, I'd want the digital storage scope!

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Ben Jackson AD7GD

http://www.ben.com/

Thanks Ben, some more good stuff to think about. I've never actually used a scope to do anything real. Way back a few class experiments with lissajoux figures and the like, and I've watched the techie at work a few times. I've got a lot to learn before I lay out the readies. Cheers, jack

Hi Jack Definitely get yourself an analog oscilloscope. New ones are poor value, you can get a refurbished unit on eBay or test equipment suppliers for much less.

20MHz dual channel is basic entry level oscilloscope. Although if you are looking at 2nd hand refurbished units then 50MHz or 100MHz would be more useful.

Once you have a proper analog oscilloscope *then* think about getting a digital PC based oscilloscope. Regards of what PC oscilloscope makers claim, they are not a replacement for a good analog oscilloscope.

In todays digital world you really need both, esp if you are into data logging type stuff, digital etc. Digital scopes let you capture single shot events that analog oscilloscopes can't. And analog scopes give you the real-time feedback and resolution that digital scopes can't give you (unless you pay >$$$$).

Digital scopes are tricky when it comes to "bandwidth". They will have a "sample rate" which has nothing to do with the analog "bandwidth". A

*good* digital scope will operate in "real-time" and have a sample rate that is at least 10 times greater than the analog bandwidth. e.g. 1GS/s for 100MHz analog bandwidth.

Dave.

Not to react too grumpily to your grumpiness , but your scenario seems overly conservative and arbitrary. I think very few people would agree that 600 samples are required to adequately view one cycle of a sine wave... 20 is probably more like it.

If the OP is interested, he can download my Daqarta software and use it to look at the output of the built-in signal generator. Judge the display quality as you raise the generator frequency. The trace area is

512 samples wide (unexpanded) and the sample rate (set by the X-axis dialog) is typically 44100 or 48000 samples per second, so you can figure out the relative pixel resolution of other digital scopes.

However, one of the big advantages of a digital scope is the ease of getting a spectrum display, which is often much more useful than a waveform display at audio frequencies. You probably won't find a spectrum display on any entry-level hardware scope.

Note that although you can use Daqarta as a digital scope/spectrum analyzer for audio frequencies, I am not suggesting that it is in any way a replacement for a fast hardware scope. (I have a 100 MHz scope on my bench as well.)

One other advantage of a digital system is that the signal generator can be precisely and repeatably controlled, and typically can be synced to the input process to allow synchronous signal averaging. For a stimulus-response type test, that allows you to recover responses that were totally buried in noise, with no waveform distortion or rounding such as would be caused by a filter.

By the way, the Daqarta signal generator is yours to keep, absolutely FREE, just for trying Daqarta. Not available in any store!

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!

If you are in Sydney then I have an old 30MHz analog scope I'm looking to get rid of pretty cheaply...

Dave.

That is basically a data logger and not an oscilloscope. The 200KHz sample rate makes it only good for audio use up to 20KHz (giving you

10 samples per cycle at that frequency, a rule of thumb). Seems like it only has a single input range as well, that is also very poor.

It's just a toy, don't waste your money.

Dave.

Thanks for the offer Dave, but I'm way over in the Golden West, and not yet in a position to invest in a CRO. Just trying to learn about them at the moment. jack

Thanks for that, Bob. Most interesting. I will give that a go, Cheers, jack

Note that when you install Daqarta you are *supposed* to get

30 sessions/30 days free trial of everything, after which only the inputs stop working. You are welcome to use it like this as a fancy signal generator or WAV file analyzer, etc, for as long as you like. However, some people report that they get a "NO trials remaining" message on the initial install. If you don't want to test the input functions, you can just use the signal generator as-is. But if you contact me (use the Contact Us form on the site) I will be glad to create a custom trial key for you that will give you the original 30/30 trial. (The trial problem will be fixed in the next version, in about a month.)

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!