Is Bandwidth/memory depth a waste of money in oscilloscopes?

[Fungus]

A car with squeaky windshield wipers and sloppy steering will still get me to the train station in precisely the same time, and I didn't ask for a car that was "comfortable" I asked if a car with fuel injection and capable of 160 kph might be important to me in driving to the train station. A "comfortable" car might be important to you, but what makes you think I'm interested in paying more for that?

He is, of course, exaggerating. None of the oscilloscopes listed so far is anything like a car with "wobbly wheels, squeeking wind shield wipers, sloppy steering, etc". People who drive Mercedes may look down on Ford Fiestas but Ford Fiestas are good little cars (and very well equipped these days).

If you know forums then you should have already guessed there's oscilloscope snobs, too...

Stepping from a CRO to a DSO there's a few simple things to understand.
Traces won't appear as crisp and at first you think WTF, what's all this noise ? Check for Daves vids on why DSO's appear noisy.

Yes, the world of beautiful smooth green traces will end but you'll soon realize a DSO is capable of showing a lot more real information than a CRO.

Here's the video:

[tautech]

Here's the video:

You forgot there's two of them !
https://www.eevblog.com/2014/04/27/eevblog-610-why-digital-scopes-appear-noisy-part-2/

[Mr Nutts]

Not hantek because you’re paying to have every corner cut. 8 bit sample size. Bad.

Aren't most digital scopes 8 bit? 

Personally I’d go for the Rigol DS1054Z. 4 channels, crack it to 100Mhz and 24M sample depth and 12 bit ADC. 

Since when does the DS1054z have a 12bit ADC? 

[bd139]

You are correct. My bad. Assumed it had HMCAD1520 ADC in it but it's a HMCAD1511. I shall get my coat 

[Muttley Snickers]

@Pete F

There is a Hantek MSO-5074F for flaky currently listed on ebay.au for $275 and is open to offers, this is a 70 MHz scope with 1Mpts memory depth, 8 channel LA (3 volt max) and a large 800 X 480 screen, the item is described by the seller as fully operational but a bit flaky and frustrating at times to use. Anyway, it appears to be within your budget and at that price you can easily afford to grab it, have a play and then either keep it if found to be suitable or sell it off again at little risk. Certainly worth a closer look if you are set on a Hantek, sorry I cannot post a link to it from this device.

[nctnico]

A car with squeaky windshield wipers and sloppy steering will still get me to the train station in precisely the same time, and I didn't ask for a car that was "comfortable" I asked if a car with fuel injection and capable of 160 kph might be important to me in driving to the train station. A "comfortable" car might be important to you, but what makes you think I'm interested in paying more for that?

He is, of course, exaggerating. None of the oscilloscopes listed so far is anything like a car with "wobbly wheels, squeeking wind shield wipers, sloppy steering, etc". People who drive Mercedes may look down on Ford Fiestas but Ford Fiestas are good little cars (and very well equipped these days).

How do you manage to write so much nonsense again?  Look at my posts on various pieces of equipment more carefully and you'd know I have a whole range of test equipment. From cheap Ebay stuff to really high end stuff. Whatever gets the job done quickly and without being annoying.

[Pete F]

Thanks. I thought Dave's video on "noise" was excellent. I'd seen that before asking here as part of my research. I'd always thought it was part of the ADC process and thought, oh man, that is going to do my head in! I had no idea until that video I'd been looking at it all along and just never knew!

Yes I spent something like 7 years in college trying to stay awake while a lecturer tried to do otherwise, so I do have a vague idea of what a square wave is My point is that I'm probably not going to be designing this stuff, building it maybe, but unlikely to be designing it. I've never once, in my career, had any need to examine the leading edge of a clock frequency! It's either A) there/vaguely on frequency = good B) Not there = bad.

To put this in further perspective, I bought that 2215 something like 15 years ago, quite used, because it was something similar to what I mainly trained on (I think they were 2213s if my memory hasn't completely gone). In the past 15 years I have probably used it, maybe, 7 hours use? ie it would be used maybe 30 minutes PER YEAR on average. Now that admittedly fluctuates, and when I move house I will have a dedicated small electronics area so expect that to come up a lot. But that should put things in perspective. That's almost certainly why it now failed; electronics, especially power caps, don't like to sit idle! It's a bit of a PIA to get that 2215 out from storage, set it up on the kitchen table, and try to get organised. One day that will hopefully change.

Why did I get it out now you might be wondering, a lucky year? Well I discovered that my main hifi amplifier (mid to higher quality) had a channel not working. A bit of poking around and I could see it's not being biased on. Not exactly a space shuttle launch we're going for in that repair! I also discovered my CD player was playing up (hey I never have time to sit down and listen to any of this these days). Again it's an audio fault and shouldn't be a big deal.

The future? Well who knows. I still have an interest and would like to get back in to it more when I get more opportunities. But that's the reality of where I'm at now. If it means spending A$600 on an oscilloscope then that's how much they cost. Pay the fare and hop on the ride. But if I can get something that might only last 500 hrs before it blows up, or isn't the best quality, or can't measure the nearest black hole, etc and only costs A$350, then why would I want to spend $500. That's probably a hundred bucks an hour for its expected life and my use. Even the aforementioned hookers are cheaper than that!!!

[bd139]

Sounds like you need to spend $20 on caps and save the rest for hookers and beer.

[Pete F]

@Pete F

There is a Hantek MSO-5074F for flaky currently listed on ebay.au for $275 and is open to offers, this is a 70 MHz scope with 1Mpts memory depth, 8 channel LA (3 volt max) and a large 800 X 480 screen, the item is described by the seller as fully operational but a bit flaky and frustrating at times to use. Anyway, it appears to be within your budget and at that price you can easily afford to grab it, have a play and then either keep it if found to be suitable or sell it off again at little risk. Certainly worth a closer look if you are set on a Hantek, sorry I cannot post a link to it from this device.

Thanks, yes I saw that. However I already have one oscilloscope that doesn't work and don't want another I thought it was a bit overpriced to be quite honest. They're not all that much more than that new from what I've seen and shopping around.

My "budget" is what it takes to get the job done. To me this isn't anything to get very excited about and it's just a tool with about as much interest to me as a pair of side cutters. Having said that I do appreciate quality and aren't interested in buying rubbish I will just be disappointed/frustrated with and won't do the job. I'd rather have a lower spec but better quality tool is of much more value to me than a POS that lets me down, or a "brand" name that doesn't do much. A bit of a balancing act I guess.

[epongenoir]

I'll just add my 2 cents.
I am graduating in electronics engineering but always had a passion for it since I was a kid.
I had a really old 4Ch Tektronix 2465 I bought on Ebay, but I needed a DSO (digital electronics, waveform run/stop..), so I sold my old one and bought a Siglent SDS1104X-E.
I've been amazed on how capable the little beast is in terms of responsive and nice UI, functions, boot time, few clutter on screen..
(BTW it can be hacked to a 200Mhz BW, look in this thread: https://www.eevblog.com/forum/testgear/siglent-sds1204x-e-released-for-domestic-markets-in-china/msg1612639/#msg1612639).
I have used a Rigol a couple times before the Siglent but never had the same feel for that instrument.
If you plan to use a bit of advanced functions or something a tad more serious, I'd recommend the same one I bought.

[Fungus]

How do you manage to write so much nonsense again?  Look at my posts on various pieces of equipment more carefully and you'd know I have a whole range of test equipment. From cheap Ebay stuff to really high end stuff. Whatever gets the job done quickly and without being annoying.

Then you know you're exaggerating. DSOs in the $400 range are Ford Fiestas, not clown cars.

[Pete F]

Sounds like you need to spend $20 on caps and save the rest for hookers and beer.

Unfortunately I think this hooker will give me a dose of something even the strongest penicillin won't help!

If it was just the one cap I'd throw one at it and move on. But as I said above, it's time for the old girl to go. I don't have the time to be constantly fiddling with tools. I want to turn them on, they work, I do what I bought them for and then I turn them off again. What shouldn't be overlooked is a modern DSO can do a heck of a lot more than my old 2215 ever could. Something I've been reminded by, as I dropped my multimeter a while back and while ruggedized it still manage to go a bit flaky. Another thing I'll need to replace It's been a week of the magic smoke fairy dancing around my place I tell you!!!

[rf-loop]

So to bring the topic bang to the original question I'm keen to know how a (relatively) high bandwidth oscilloscope (let's say 100 MHz) would help somebody who generally works in the audio range of frequencies. Maybe clock freq, but that's about it at this stage. I personally can't see how 100 MHz has even the vaguest assistance, but that's why I'm here to ask.

The "MHz" in the bandwidth rating of an oscilloscope usually isn't related to the frequency of the signals you're looking at.

Any signal other then a perfect sine wave has harmonics. These harmonics can be much higher frequency than the base frequency. eg. Square waves have infinite harmonics, to see a perfect square wave on an oscilloscope screen you need infinite bandwidth. This is true even if you're only looking at a 1Hz square wave!

It's also true of zero Hz square waves. A single transition from low to high voltage may have infinite harmonics. You might need a lot of bandwidth to see the detailed characteristics of a single rising edge.

So .... it doesn't matter if your clock freq has a base frequency in the audible range, you need a lot more than audio range in your oscilloscope if you want to look at it.

Only theoretical ideal square wave or transition (step) what have 0 rise and/or fall time have infinite harmonic frequencies. And these do not exist in real world.
Limited rise time signal do not have infinite harmonics and all signals in practice in real world have limited risetime.


-------------------------------
Overall:

So, depending how accurate measurements need do example for risetime this is key factor what BW (risetime) oscilloscope is needed. If risetime what need measure is 1.75ns and it need measure with no more than around 2% error it need 1GHz oscilloscope. (bit more if it have "brick wall" type frequency response shape) Why I take here just 1.75ns. Because it is typical 200MHz oscilloscope risetime. Common "rule of five" is, you need 5 times faster oscilloscope risetime what is signal risetime if you want "good" accuracy for measure risetime.

For pulse/square type of signals (aka "for digital signals") it is best to define needed BW (risetime) using some estimate of fastest rise/fall times what need observe.
If fastest risetime is 3.5ns and we can accept 40% error on rise time measurement then 100MHz scope is enough.
Now with low frequency pulses and if want look these on the screen and also zoom in to rising / falling edge for observe these edges together with visible whole pulse period there nee be also enough memory what make possible to keep sample speed enough high.
It need also note that some older technology entry level scopes may have two kind of memory. Full speed and then reduced speed. Example some scope may have only quite short fast memory and then example 1M "long" memory is only half speed. Many times product brochure do not tell it clearly or not at all.

[GeorgeOfTheJungle]

I have a hantek 5072p and it's pretty good, works well, a pleasure to use, haven't had a single problem yet (+5 years), and was cheap, 180€ IIRC. Buy one of these if you like it, it's not an Agilent but it's fine.

[rstofer]

So to bring the topic bang to the original question I'm keen to know how a (relatively) high bandwidth oscilloscope (let's say 100 MHz) would help somebody who generally works in the audio range of frequencies. Maybe clock freq, but that's about it at this stage. I personally can't see how 100 MHz has even the vaguest assistance, but that's why I'm here to ask.

For audio and other low frequency sinusoidal signals, high bandwidth isn't necessary.  It is an indication of the quality of the front end but so what?  You simply don't need bandwidth - today.

Where it comes up is verifying signal integrity of square waves where we NEED high bandwidth to include the various harmonics.  With a 100 MHz scope, if we want to include the 9th harmonic of a square wave, its fundamental frequency needs to be around 10 MHz (leaving a little on the table to stay away from the knee).
 But that 100 MHz number is pretty low when thinking in terms of 50 MHz FPGA signals.  For folks involved with digital signals, bandwidth is everything.  Except channels...

More channels is good in the digital arena - not an area you appear to be interested in.  Fair enough!  Four channels works great for decoding the SPI bus and that's why I bought the Rigol.  It's my go-to scope but I'm keeping my Tek 485 for bandwidth.

The DS1054Z is being offered with all the options except 100 MHz bandwidth and it may be one of the low price leaders.  I wouldn't have any idea how equipment is priced in Australia.  From what I have read, US prices are a good deal lower.  The Rigol has been out for quite a while and has gone through several iterations of the firmware.  The usability bugs have been worked out.  Siglent is taking an aggressive approach to fixing their problems with the new SDS1204X-E (or 1104 or 1202) but I haven't been following along.  I am seriously interested in the 200 MHz 4 channel variant (SDS1204X-E) but I just haven't outrun the DS1054Z, yet...

I think the only way to make a choice is to create a spreadsheet with features and costs.  Sort the data in order of preference and then start reading reviews.

The idea of having an interest in only lower frequencies comes up all the time.  A lot of folks are interested in audio and not interested in digital.

[stj]

2 pages and still arguing?

just buy a damned Riglent and be happy! 

[bd139]

Or buy a DSO138, cry for a bit and fix the 2215, nodding approvingly at the money you now have to spend on a new DMM

[maginnovision]

Another option would be hantek 6022 with openhantek software if you'd rather go cheap for something you basically don't need.

[Fungus]

A lot of folks are interested in audio and not interested in digital.

just buy a damned Riglent and be happy! 

"Audio" people might be better off with the GW-Instek. 

[bd139]

Audio people would be better off with the one with the least shit FFT.

[GeorgeOfTheJungle]

just buy a damned Riglent and be happy! 

Riglentek 

[David Hess]

Since it has delayed timebase capability and peak detection, it does not need a large record length as much as a modern DSO which lacks these features.

All modern DSOs have delayed time bases! That has been pointed out before. You can set the trigger point outside the screen and there you have it.

It has nothing to do with the screen or display record.  None of the single timebase DSOs I have evaluated allowed the trigger to be moved outside of the waveform record.  But if the waveform record is long enough for the application, then this is not a problem except perhaps for performance when processing a long record length.

Where this becomes a problem, and this was discussed on these forums more than a year ago, is things like measuring jitter in a 1 pulse per second GPS signal.  20M points over 1 second is only 20MS/s yielding 50 nanosecond resolution which is worse than the jitter of many GPS 1 PPS signals.

The thing about this which really annoys me is that manufacturers like Rigol deliberately obscure this in their documentation by confusing delayed sweep, pan, and zoom functions.  The only way I have found to reliably know what a DSO can do is look for the B trigger capability; if it is lacking, then the DSO is limited to pan and zoom within the waveform record.

Here is another discussion of the same problem:

https://www.eevblog.com/forum/testgear/rigol-ds1054z-triggering-question/25/

If what you said was true, then magnification (delayed sweep according to Rigol) would allow the fastest time/div and sample rate at any point within the waveform record under all conditions.

PeteF, none of this would matter for power supply and audio applications so ignore this limitation.  It would be expensive to avoid unless you want to buy a used instrument which I do not recommend unless you would enjoy refurbishing your 2215.

Traces won't appear as crisp and at first you think WTF, what's all this noise ? Check for Daves vids on why DSO's appear noisy.

Dave never actually made objective noise measurements.  Most DSOs are both subjectively and objectively noisier.  The subjective noise in the display is just because they are cheap.  The objective noise is due to poor design and additional quantization noise.

You are correct. My bad. Assumed it had HMCAD1520 ADC in it but it's a HMCAD1511. I shall get my coat 

Even worse in averaging or high resolution mode, it is *still* 8 bits.


Instead of thinking in terms of bandwidth, think in terms of rise/fall time.  100MHz is 3.5 nanoseconds.  50MHz is 7 nanoseconds which is still sufficient for even switching power supplies.  20MHz is 17.5 nanoseconds which will be marginal for switching power supplies.

[nctnico]

Since it has delayed timebase capability and peak detection, it does not need a large record length as much as a modern DSO which lacks these features.

All modern DSOs have delayed time bases! That has been pointed out before. You can set the trigger point outside the screen and there you have it.

It has nothing to do with the screen or display record.  None of the single timebase DSOs I have evaluated allowed the trigger to be moved outside of the waveform record.  But if the waveform record is long enough for the application, then this is not a problem except perhaps for performance when processing a long record length.

I just tried with my GW Instek GDS2204E and it does exactly what you describe is not possible. I could try some of my other scopes as well but I'm pretty sure I get the same result. I get the feeling you have tried a few very limited DSOs and now map that information on all other DSOs. Doing a delayed trigger is pretty easy to implement in a DSO so there is no reason not to have it.

[iMo]

@PeteF: this topic you have started repeats periodically since very existence of this forum You may find dozens of similar threads where an OP is asking which oscope to buy.. And you get always the same answers or "recommendations", from usually the same posters..
Nobody helps you here with the spoilt for choice. The final decision is up to you. There are several oscopes which may fit your needs, but you have to undergo the risk of the purchase. When you start to dig into very technical details (and analyze or study all the hw/sw bugs/issues) you most probably will not buy a new DSO oscope and you rather repair the old TEK one

[Pete F]

@PeteF: this topic you have started repeats periodically since very existence of this forum You may find dozens of similar threads where an OP is asking which oscope to buy.. And you get always the same answers or "recommendations", from usually the same posters..
Nobody helps you here with the spoilt for choice. The final decision is up to you. There are several oscopes which may fit your needs, but you have to undergo the risk of the purchase. When you start to dig into very technical details (and analyze or study all the hw/sw bugs/issues) you most probably will not buy a new DSO oscope and you rather repair the old TEK one

Well once again I didn't ask an opinion on which 'scope to buy, so I don't know why people insist on making specific model recommendations! I don't need anyone ot make up my own mind, I have one of my own.

I asked, specifically, whether bandwidth would be of any use to me. Having very specifically described my application, use, and period of use.

I also asked how much memory depth would affect that situation and why.

If somebody wants to tell me what they use and why it might be good for me, they can knock themselves out, but I won't be taking much notice until I'm very happy with my understanding of the first two questions.