Electronics > Beginners
Oscillo-confusion MHz GSa/s wfm/s Mpts
FriedMule:
That helped me a lot and maybe I should define the data before the model?
Am I understanding correct in these data titles?
All with the thought on selecting a "do whatever beginner scope that I can use to most run of the mill electronic)
bandwidth (Maybe not so extremely important but 100MHz+)
sample rate (1GSa/s+)
memory depth (As large as possible)
resolution (as many bit as possible "16bit best)
update rate (faster is better)
Capture rate (higher is better)
What would you put in as value for getting a cheap, max 1.000$ but "best" scope?
james_s:
--- Quote from: vk6zgo on January 02, 2019, 01:04:03 am ---There are times when you want to look at signals with quite high frequency components, whilst using a very long time/cm setting.
The classic case is looking at analog video at field rate.
DSOs with very small memories commonly reduce the sampling rate savagely at such settings, to the point where the required display is lost in a forest of aliasing.
The early DSOs ( & some currently available really cheap ones) cannot even display analog video accurately at line rate.
OK, analog video is no more, but try looking for 50/60Hz "hum" on any pulse train with HF components!
--- End quote ---
Analog broadcast TV is gone but analog video is alive and well. I use it for the FPV video link on a couple of my RC airplanes and multirotors, it's widely used in retro computers and video games, amateur broadcast, many security cameras are still analog, it's not uncommon that I find myself looking at a video waveform.
tggzzz:
--- Quote from: vk6zgo on January 02, 2019, 01:04:03 am ---
--- Quote from: tggzzz on December 31, 2018, 02:40:55 pm ---Bandwidth and samples/second are completely independent. Bandwidth is all that matters in a scope, except to salesmen. I have an ~4GHz scope with ~40kS/s.
Apart from that fundamental, there are many threads on "scopes for beginners" on this forum.
The key points are to define what you will use the scope for, and whether you have other necessary equipment. Plus you shouldn't forget the cost of probes :)
--- End quote ---
There are times when you want to look at signals with quite high frequency components, whilst using a very long time/cm setting.
The classic case is looking at analog video at field rate.
DSOs with very small memories commonly reduce the sampling rate savagely at such settings, to the point where the required display is lost in a forest of aliasing.
The early DSOs ( & some currently available really cheap ones) cannot even display analog video accurately at line rate.
OK, analog video is no more, but try looking for 50/60Hz "hum" on any pulse train with HF components!
--- End quote ---
The early digitising scopes were awful to use, except in some circumstances. Hence the correct statement that analogue scopes were usually better.
It is only relatively recently (by my standards!) that digitising scopes have been equally usable.
tggzzz:
--- Quote from: rstofer on January 02, 2019, 12:37:05 am ---
--- Quote from: FriedMule on January 01, 2019, 08:52:54 pm ---Maybe I have read wrong but for me it sounds as some of you writes:
Buy high bandwidth, you will rarely use 4 channels
and other says
Buy 4 channels, you will properly not use high bandwidth anyway?
--- End quote ---
It goes either way!
Using 4 channels may never happen for some users or it may happen all the time. It was my most important purchase criteria. I already had 2 channels (analog scope). Since I had never used a DSO, I had no idea how important Single Shot would be. It solves so many problems.
In the old days of the analog scope, I would have to butch up my logic or code in order to have a pulse train repeat often enough to stay on the screen. With single shot I don't need to modify anything. I just select single shot and one pass is all it takes. This is a HUGE deal and one of the great benefits of the DSO.
--- End quote ---
As you note, it is usually possible to design and implement a circuit in such a way that the waveforms are repetitive - in which case single-shot is not necessary.
However, there are a few events that are one-offs (e.g. monitoring bomb explosions, PSU startups), and for these a storage scope is necessary. Before digitising scopes, we had analogue storage scopes - and they were as horrible to use as the early digitising scopes were for repetitive waveforms.
--- Quote ---High bandwidth will never be an issue for those interested in audio.
--- End quote ---
There bits/resolution and linearity are probably more important. The Analog Discovery is pretty good in that respect.
--- Quote ---My interests are up to around 50 MHz on uC pins and usually not that high. Maybe something in the 2-5 MHz range.
--- End quote ---
Ahem. That 2Mb/s signal could have components above 1GHz, depending on logic family. But you know that!
Personally I'd use a cheap and nasty LA to capture/decode such signals.
rstofer:
--- Quote from: tggzzz on January 02, 2019, 01:52:31 pm ---
--- Quote from: rstofer on January 02, 2019, 12:37:05 am ---High bandwidth will never be an issue for those interested in audio.
--- End quote ---
There bits/resolution and linearity are probably more important. The Analog Discovery is pretty good in that respect.
--- End quote ---
In my view, the Analog Discovery is unappreciated. The lab courses associated with Digilent's Real Analog course demonstrate many of the features. It truly is an electronics lab in a small box.
--- Quote ---
--- Quote ---My interests are up to around 50 MHz on uC pins and usually not that high. Maybe something in the 2-5 MHz range.
--- End quote ---
Ahem. That 2Mb/s signal could have components above 1GHz, depending on logic family. But you know that!
Personally I'd use a cheap and nasty LA to capture/decode such signals.
--- End quote ---
Whether the LA can display setup and hold times will be a function of its sample rate. I have a LA that will sample at 200 MSa/s which is pretty good but before I went for one of the $8 units, I would want to look carefully at sample rate. My scope will sample at 1 GSa/s which will more accurately display the time difference between events.
ETA: True, the DS1054Z will only sample 4 channels at 250 MSa/s but I could momentarily be more selective and display just 2 channels with a sample rate of 500 MSa/s.
At high SPI rates, a LA sampling at 100 MSa/s might be just fine.
ETA: Logic Analyzers will have much better triggering options. I sometimes have to add logic just to create a trigger when using a scope. There are a number of reasons that LAs are popular.
https://sump.org/projects/analyzer/
Note how the sample rate drops when the device is used for state analysis and the device under test provides the sample clock. State analysis is my primary use of a LA. I don't care what the state of logic signals is relative to some arbitrary internal LA clock, I want to know what their state is relative to the internal logic clock.
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