Hi Guys - been lurking for a long time, have seen "whats the best scope to buy" many times, so finally decided to register and post my 2c (ok, more like 2Kc).
I almost always see three answers regarding the DS1054Z (or any other "entry level" scope):
1) It's awesome, just buy it.
2) It's chinese crap, don't buy it.
3) It's too slow even when unlocked to 100Mhz, don't buy it.
I don't find any of these answers to be all that useful.
You really need to consider what you will be using the scope for. A major question is Bandwidth? and the usual response is "get as much as you can".
If you do that, there are two very likely results for most people:
- you will pay more than you need to for your scope.
- you will give up features/capabilities which might be more useful to you on a daily basis.
Bandwidth is the most expensive "feature" of a scope by far - Sample rate also falls into this catagory. it takes real hardware to get high bandwidth and single-shop capture rates and regarding these two things, I classify scopes into into three very broad classes:
1) uber-expensive, ultra-high bandwidth, crazy sampling rates... (>1Ghz)
You need one of these if you are designing VERY fast circuits, which might include:
- modern CPU/MEMORY systems
- Modern signal transport (networking, digital video, very high speed specialized bus etc).
- Radio where you actually need to look at the RF signal shapes, reflections etc.
- Power systems where you need to see very small/fast glitches etc.
If you are doing this, you should already know what specs. you need for your scope. (if you don't I certainly hope you are not the lead designer on the project).
2) mid-range high-bandwidth/sample rate (200-600Mhz)
Possibly useful to someone who has recently graduated from category 3 below, or has to maintain older fastish equipment, but really today you seem to need "uber-fast" or "entry level" (there are or course exceptions).
3) "entry level" 50-200Mhz general purpose low-cost scope
If you are doing things like:
- Dabbling in a home lab.
- Restoring vintage equipment (Computers, Audio, etc.)
- Building/repairing older embedded systems (Ie: the CPU is a DIP or early SMT)
- Working with pre-built development systems: Arduino, STM32, PIC and others.
- Working with a SOC where the fast stuff is inside the chip and only peripheral on the outside.
- Looking at "normal" serial busses and CPU controlled I/O bits.
You don't need 200Mhz, you don't even need 100Mhz (I know people will argue).
Keep in mind that even though your Raspberry PI may be 1.2Ghz and have 900Mhz RAM, these parts are located in a very small part of the board that you will likely never have to probe. Most of signals of interest in these types of systems will be a few Mhz or slower.
Regarding sample rate.
Keep in mind that the analog bandwidth of the scope is NOT the maximum square wave it can see without degradation. It is the frequency of sine wave that will be diminished 3db by the scope electronics. The scope will see higher frequency components than that, but at an ever reduced amplitude (until it's just noise).
Nyquist says that we only need 2x the bandwidth, however that is to reconstruct a sine wave, and if you already know it's a sine, why not just use a frequency counter and voltmeter?
I use this "rule of thumb" regarding sample-rate vs analog bandwidth.
>10x is "really good"
10x is "quite good"
5x is "ok"
<5x is "pretty bad"
Applying this to the DS1054Z, we see that:
1CH 1G/50 is "really good"
2CH 500M/50 is "quite good"
4CH 250M/50 is "ok"
So I would say the 50Mhz DS1054Z is a terrific scope from this viewpoint.
If you apply the bandwidth hack, or have a 100Mhz/1GS scope, then it becomes:
1CH = 1G/100 is "quite good"
2CH = 500M/100 is "ok"
4CH = 250M/100 is "pretty bad"
That's not to say that a 4CH 100M 1GS scope isn't useful, but beware of the limitation if you are trying to use it near max bandwidth with all four channels running. For that matter, be aware of the limitations of any of your tools when doing a particular job.
The next "good thing" to have is memory depth. The more samples you can store, the longer a series of events you can capture and zoom in on to see the details - it really helps.
Channels: 2 channels is 100x better than 1 channel. With 2 channels, you can compare two signals in real-time, or in a single-shot capture. Unless you are doing something really primitive, you probably want at least 2 channels. Four channels is "really really nice" but I wouldn't call it essential. But it can be so much easier to look a things like serial buses when you can see data in, out, select and clock all at once.
Who am I and why do I think I know something about scopes? I'm primarily a very-low-level software guy, who has built and interfaced a pretty good share of hardware over the 40 years or so that I've been doing this. My 2Kc comes from a professional lifetime of actually using various scopes in a cost-conscious 1-man company (and a fair bit of hobby time too):
My first scope was a home-built analog (
http://www.dunfield.com/oscope.htm ) which probably had only a few Mhz bandwidth and basically no measurement capability (not even a scale on the screen). Being young and too naive to know that it was "useless" I learned more with this scope than I have with probably any other scope since.
After passing through a few low-end commercial analog scopes (which did have scales :-), My first digital/storage was a Gould OS4000, 10Mhz, 1.8Mhz sample rate, 1K samples. Not being aware that it was "too limiting" to be useful, I designed MANY products with this scope, and used it right up until I was working with ARM-7 systems.
Counting on my fingers, I currently have 6 ponies in my scope stable. I find these cover more than my needs (could probably get rid of a few of them - yeah, I really should... I'll think about that... someday... maybe...):
1) DS1054Z (4ch 50Nhz 1GS-total)
Yes, I have one - I bought it for 4 channels and the deep memory (and good luck prying it from my fingers). I HAVE NOT upgraded it to 100Mhz although I may after the warranty expires. 50Mhz is plenty for almost all of the stuff that I need a 4ch/deep scope for.
2) Tek TDS210 (2ch 60Mhz 1GSx2)
I got it for the portability and simple Tek controls. It was my daily driver and I still use it a fair bit, but the Rigol is taking over.
I keep it because it has separate vertical controls and the UI responds faster than the Rigol.
3) Tek TDS380 (2CH 400Mhz 2GSx2)
My fastest scope - I keep it around in case I ever need to look at something fast-ish ... but it's big and most of the time it sits in the corner.
Has only 1K sample storage, so not great for zooming in on long stream events.
4) Tek 2232 (2CH 100Mhz 100Mx2)
I keep it because it is The only scope I have left that still can operate as a fully analog. I also find it easy to use (and it has to cool Wizard easter egg :-)
5) UNI-T UT81B (1CH 8Mhz 40MS) - SCOPEMETER
Not a fantastic scope or meter but it fits in my portable toolkit and is useful enough that it's handy to have when nothing else is available. Also good for working on non-ground referenced things.
6) JYtech DSO-138 (1CH 1MS)
Bought out of curiosity to see if a $15 scope actually worked. Answer: Yes, with limitations but the test wasn't valid because I didn't realize till after I bought it that the $15 ones on Ebay are knock-off clones and JYtech gets nothing. I take solace in the fact that I don't actually use it.
If I had to have only one, it would probably be the DS1054Z - I would say that it covers 95+% of what I use a scope for on a day to day basis, and the advantages of 4CH and deep memory outweigh the benefits of my other scopes (for me at least). 2nd keeper would be the TDS380 for the speed, but I really don't use it much these days and probably wouldn't miss it.
Whew... sorry to be so long winded.
Dave