Best oscilloscope choice?

[Paul-R]

EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE

Relationship between: - Frequency of circuit under test and Mhz, sample rate of scope needed

EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
.
Understanding this is vital. Can someone explain how to arrive at the required Mhz and sample rate needed to examine frequencies under test?

(Slow running motors should be able to use the Winscope software, with probes going into the soundcard)

[TinselKoala]

1. No, I don't have a Tek 465, but they are fine scopes, if a bit complicated for a beginner. If you buy one make sure it's working 100 percent. They may have problems with switches and pots, due to age, but these are usually easily fixed by exercise and cleaning. Ask the seller, make sure you can return it if not working properly.

2. Don't buy a single-channel scope. These are special purpose items and are not as useful as a two-channel instrument. You will often want to look at the relationship between two (or more) signals and there is no way to do this if you only have one channel available.

3. Stay away from very old scopes like that Eico. They will probably need to have most or all of their electrolytic capacitors replaced in order to work properly. Unless you are a collector or just like fixing old stuff, it's not worth it for someone who wants an instrument that is actually useful on the bench.

4. The general rule about bandwidth is 5 times the fundamental frequency of the signal you want to examine. So a 100 MHz scope will "honestly" tell you what's going on in a 20 MHz signal, as far as risetime and amplitude is concerned. Of course you can use the scope for higher frequencies, but it won't show you the true amplitude of the signal nor will it accurately report rise times or other fast transient phenomena. This is true whether the scope is analog or digital. But DSOs have another thing to worry about: Aliasing. They can show you a completely different waveshape than what you are feeding into it, depending on sample rate. This is one thing you don't have to worry about with an analog scope.

5. While (almost) any scope is better than no scope at all, I would recommend staying away from "sound card" scopes or USB scopes that use your computer as display and control. Sound-card scopes have very low bandwidth and are clumsy to use. USB scopes can be good, but the good ones are as expensive as a low-end bench DSO. The cheap ones like the 20 MHz 60-dollar Hantek... well, I suppose they are better than no scope at all, and they do come with a set of probes that would cost about 20 dollars just on their own.

My advice: for between 100 and 200 dollars, look for a simple analog scope like the Tektronix 2213a or 2215a or similar 60-100Mhz bandwidth 2-channel unit. For 200-400 dollars --- save up and get something like a Siglent 1000 series or a Rigol DS1054z. If you absolutely must have a scope right now and you can't afford more than 100 dollars for the foreseeable future, consider a USB scope like the 20MHz Hantek, but beware....

And have fun! The oscilloscope is the King of Test Equipment and no electronics experimenter's workbench is complete without one.

[Paul-R]

That's a handy rule of thumb, TK. x5.

What about sample rate? How does that fit in (apart from some sort of "the more the merrier" yardstick?)

[sm0ky2]

back in the late 80's, early 90's they developed processors that clocked in the Ghz range,
and along with them came scopes that could read the signals.

of course, just like most of the "real technology" of our world, we don't get to play with them for about 50 yrs after development, and while that time is approaching, they are still tens of thousands of dollars, and out of reach of the average person.

By the time we can get them, our computers will be running on synthetic diamond processors clocking in the TerraHertz, and most people wont see THOSE scopes till the year ~2058
(THz O-scopes were fully functional by 2008, using two different technologies)

TK gives good advice on the low-range scopes, I've owned a few, but most of what I care to play with these days is far beyond the reach of an affordable scope.

really kewl stuff happens at wavelengths approaching the atomic resonance scale 

[ayeaye]

All i know about how the bandwidth of an analog oscilloscope is defined, is that it is the frequency where there sine signal is reduced to 70% of its original. Higher than that frequency, and almost nothing comes through. And this is only about sine wave, any harmonics you want to see, must also be within that bandwidth.

What concerns the USB oscilloscopes, then i rather prefer to have a glorious decent old scope, with all the funny things on it, than this small cheap box containing some questionable electronics, and you can get it for the same price or cheaper. Also that eevblog guy doesn't quite agree with TinselKoala about these cheap USB scopes, and i trust that guy, he really knows what he says. They should start to make some cheap analog scopes for the beginners again, as they once did, but they don't, and this Sinometer is just an accident.

What concerns the Eico, i meant, who is truly a minimalist and wants to have a minimal scope, should rather consider buying that old Eico, than that Sinometer. Yes i know one may end up replacing almost all components there, but when one is such a minimalist that can go to buying that Sinometer scope, just to have a minimal scope, then much better would be to buy that Eico. Because there will be an equal trouble of doing anything at all with both of them, but when one repairs Eico, then at least one would have a useful scope, though only minimal. But this will never happen with that Sinometer scope, even when one is very good at electronics, one likely cannot make it anyhow useful, because of the flaw of just everything in it. Who doesn't want to repair a scope at all, as i said, should buy a working scope, but pay somewhat more, though not much. As i did, and i got a scope which i didn't have to repair at all, and it works well until this day.

Old Tektronix scopes tend to be expensive in ebay, and much more tricky to buy, because they are the most sought after. This is why i talked about other alternatives of old scopes, which one can get much more cheaply from ebay, but that are still good working oscilloscopes, all what a beginner may need. Like this LG (GoldStar?) oscilloscope, $110 with free shipping, it has a test signal on the screen, and it is evidently working http://www.ebay.com/itm/LG-Dual-Channel-Oscilloscope-Model-OS-5020-20mhz-/331680874379?hash=item4d39b87f8b:g:mUUAAOSwo6lWHUId . But it is likely a good oscilloscope. This was "buy it now" when i posted this, when now the seller again changes to auction, be careful and notice that and better avoid buying it, but please don't blame me then.

Old scopes should not be wasted, they should be added to the armory of overunity researchers