Recommended oscilloscope features?

[fachat]

Hi all,

I am thinking of getting me a new O'scope. As some might know I'm still using my trusty old scope I got in used condition around 1986, when it was already old.... http://www.6502.org/users/andre/petindex/imgs/osci.jpg
So it's time for a change.

Now my question is, what would be good features for a new scope? I guess from all the features I'd feel like in hacker's heaven, but it has to fit my purse too, so I have to do some priority-based selection process...

These features I think are required:
- 2 channels + (external) trigger channel
- external / internal trigger, one-shot mode (sample & hold)
- high bandwidth, like 100MHz (my 65816 already has a 50MHz oscillator which is not really showing on my current scope)
- AC/DC coupling, must be allowed to scope stuff connected to mains line
- digital scope: 1GS/s (1 Giga samples per second)
- USB connection to PC to send screenshots/samples to the PC (Linux driver preferred, operation independent from USB is a must)
- basic signal operations (add, substract the two channels)

These features are optional:
- X/Y mode
- cursors for measurements
- "accumulation mode" - not sure if this exists, continuously sample on a trigger, and add the signal to the ones already on screen (to detect glitches of say 1 in 100.000 cycles where the line looks different)
- decode and trigger on busses like I2C, SPI, RS232
- more complex operations, like FFT (= spectrum analyzer)

Some questions I have after looking at some spec sheets:

- kpts = kilo points per second? means what?
- sample memory 25kpts vs. 1Mpts? (25kpts with 1GS/s would mean samples for 25us - ok for me if I take 25 6502 cycles at 1MHz ... Makes me think about zoom into the timebase though)
- usability? Any experiences you want to share?
- cooling fan? best avoided I think
- what about delayed trigger? Do you think this is important?
- LabView?

But after all, total cost should be <1000€, the lower the better - depending on the features.

Maybe you can share some experience with me here.

Many thanks in advance

André

[ElEctric_EyE]

I'll offer some advice.

I bought a used Tektronix 2440 500MS/s dual trace scope I am very happy with for $500US from ebay last year.

If you buy from ebay, buy from a store not an individual. Then if you see something you like, check out their store, they may have something even better. A good thing about ebay is you can ask seller all kinds of questions.

High bandwidth nowadays are in the GHz range. You should be able to find a sub 200MHz 'scope cheap. Keep in mind also it will be older... IMO look for a 4 channel if you are looking in this speed range.

USB connection may be a feature of newer/more expensive 'scopes, not sure. I've seen them only on my automotive scope which is very slow and very expensive @$1200US (all digital 25MHz).

Make sure the 'scope passes self-test, user/owner manuals included, and last time calibrated. Pro's will have all these present and up to date.

Good luck!

[BillO]

The Tektronix 465 is a 100Mhz scope of the finest quality. I picked one up on ebay 2 years ago for $275, shipping in. I used to use one of these when I was a technician back in 1978. They cost more than my Honda Civic back then. Still works like a charm.

[Dr Jefyll]

I, too, suspect the best choice may be an older, used unit. (Ie, an analog scope.) I'm sure there are many vendors -- here is one I happen to be aware of (but haven't dealt with). Some of the gear from this fellow needs repair work, and is priced accordingly. So if you're handy you could really save some cash. http://www.prolexdesign.com/ (Oops, I see he ships mainly to Canada and the U.S.)

Delayed Trigger can be VERY valuable. X-Y mode isn't useful very often, but when it is, it can be downright miraculous. I wouldn't wanna be without either of these features (on an analog scope).

Quote:

IMO look for a 4 channel if you are looking in this speed range

Nice to have four channels, but having two channels is still highly workable I'd say. This also saves on the cost of the additional cables & probes, which can be quite pricey if you end up purchasing them separately.

I can't advise you Re: the newer, digital equipment, but I'll be curious to watch this topic and see what you find. I expect there's a big increase in value for the dollar(Euro) now that it's no longer necessary to include the expensive, delicate CRT assembly.

In particular, you may want to consider the digital units that work as an accessory to a PC, and use the PC's screen and keyboard. This arrangement may not be as portable as one would wish, but again the advantage is being able to offer better features for a given cost. Good luck!

-- Jeff

[GARTHWILSON]

I can't think of any particular must-haves (outside your basic features, most of which are on even a basic 20MHz dual-trace triggered oscilloscope) or any threshold beyond which it is pointless to go.  As you go up the scale, it just keeps getting better and better.  You could probably just decide on a budget and see what's available and pick one.  I would like to have four traces, but I manage to do what I need with two.  I would like to have more speed.  If I had a digital scope, I would definitely want a computer interface, including RS-232 and/or IEEE-488, possibly in addition to USB.  I cannot connect USB to older or home-made computers though.  I want the 'scope to be a standalone instrument, not dependent on a PC.  The fan is probably more valuable where you stack instruments so effective cooling requires moving air in and out the back instead of convection through the top and bottom.  I bought a Philips DSO at my last place of work and liked it a lot.  It was intended for audio though and was not fast enough for the digital stuff you want to do.  The computer could change all the settings though—vertical gain, sweep rate, coupling, etc., which I got because I thought we might use it in automated test equipment.  Edit, May 2021: My work got me an Agilent DSO1004A four-channel DSO.  I hate it!  It is so hard to use!  (And yes, I've read the manual.)  The Philips interface was way, way better.

Make sure you get a good set of probes that are suitable for the speed of the 'scope.  These are non-trivial and very expensive.

[PaulF]

Make sure you get a unit with sufficient bandwidth for your needs. For square waves, the scope needs a bandwidth of at least 10 times the wave's frequency to show a reasonable wave-shape on-screen. Thus, for 6502 & 65816 systems, the scope bandwidth needs to be at least 10 times the CPU clock frequency to show waveforms accurately.

Personally, I prefer an analog scope. Short glitches show up on an analog screen while on a digital scope at a lower sweep speed, these glitches disappear between two samples.

A second-hand scope from a company that specialises in second-hand test gear is usually the way to get the best performance for a given price, at least this has been my experience.

[GARTHWILSON]

Quote:

Personally, I prefer an analog scope.  Short glitches show up on an analog screen while on a digital scope at a lower sweep speed, these glitches disappear between two samples.

That might be a problem with scopes with a shallow memory where you can't afford to sample fast enough to see the glitch and still get the sweep time as long as you want, but he's talking about a pretty deep memory.  The Philips DSO I requisitioned and got at my last place of work had an analog mode too, but I almost never used it.  The analog is a pain for seeing things that don't repeat; so if I want to see an instruction to store a byte in a serial EEPROM for example, I have to put the computer in a loop to keep it happening while I examine it, which wears out that address on the EEPROM very quickly.  So while I can put up with an analog-only scope for digital work, it definitely is not my preference.  Edit, May 2021:  My work got me an Agilent DSO1004A four-channel DSO.  I hate it!  It is so hard to use!  (And yes, I've read the manual.)  The Philips interface was way, way better.

[ChuckT]

Other people with credentials say there is a 100 MHZ minimum and they use a TEK 2235 (2236 is more expensive) 100 MHZ scope. They are very expensive.

[BigEd]

There's one near me on ebay - does this seem like a good deal?

HP 1741A 100MHz DUAL TRACE STORAGE OSCILLOSCOPE £150

[GARTHWILSON]

Quote:

There's one near me on ebay - does this seem like a good deal?

HP 1741A 100MHz DUAL TRACE STORAGE OSCILLOSCOPE £150

Quote:

TRIGGER VIEW DISPLAYS A THIRD TRACE

That's a feature I've wished for a few times, particularly for the external trigger input wich is separate from the channel A and B inputs.

Note that it's analog storage, not digital. Still, if it's in good shape, it's a lot better than my two oscilloscopes at home, one of which I bought new 20 years ago for twice that price. (The other one was given to me.)

The price is good but the fact that there are no probes included is going to add a lot (unless you already have them).

[ElEctric_EyE]

GARTHWILSON wrote:

Quote:

TRIGGER VIEW DISPLAYS A THIRD TRACE

That's a feature I've wished for a few times, particularly for the external trigger input wich is separate from the channel A and B inputs...

Would you use phase 2 as the external trigger without wasting the channel to display the phase 2 waveform? or how would a feature like this be used?

[BigEd]

I would be thinking of triggering on RnW or on a relevant CS, as maybe that would get me to a region of interest more reliably than triggering on the clock. So, displaying the trigger might show something worth looking at. As I understand it, it gives you a third trace, so the trigger is pretty much a third channel.

I see your point though - you might want to use a channel to display the clock.

Even three channels isn't very many!

[BigEd]

GARTHWILSON wrote:

The price is good but the fact that there are no probes included is going to add a lot (unless you already have them).

There are plenty of cheap probes from Hong Kong on ebay - but there must be room for doubt. Has anyone any experience?

(I have three manky probes, to go with my inferior 'scope.)

[fachat]

I have been looking around and found that the price mostly depends on bandwidth and sampling rate. Other features seem to be mostly comparable. When it comes to my equipment I don't really trust used stuff from auction sellers if they don't have an own shop, and then they mostly sell new stuff anyway - so it's most likely going to be a new one.

Looking at the providers I know (and I trust to take care of their customers) I have short-listed these options:

- Rigol DS1000CA Series
- Tektronix TDS 1000B/2000B Series
- Instek 4102 Plus and the like

Depending on price (maybe waiting for a special offer sale) I'd like to go for a two channel digital scope with at least 1GSa/s sample rate, with maximum bandwidth that I can get. I'll probably even wait for a 200MHz bandwidth scope to get into my price range.

What do you think of this? Anything special I have overlooked? I'll probably dive deeper into the manuals of those series over the next week.

André

[ElEctric_EyE]

What are you looking to do exactly?, if I may be so bold. For sure Tektronics is a good investment! Looks all digital. I'm jealous..