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Oscillo-confusion MHz GSa/s wfm/s Mpts
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rstofer:

--- Quote from: FriedMule on January 03, 2019, 07:59:03 pm ---Right now I am thinking that better data always give higher resolution and accuracy while more channels only are useful the times I do need to measure 3+ places, is that stupid thinking or good thinking?

--- End quote ---

If the ADC had many more bits than log base 2 of vertical pixels on the screen, what would be the purpose?  Many very high dollar scopes are still using 8 bit ADCs.  Oh, I guess you could download the conversion data to a PC and produce a much higher resolution display but before going to all that work, check the specified accuracy for the scope itself.  It's not going to be a 0.001% device.

Scopes are 'about' kinds of measuring tools, you don't get many digits of precision eyeballing the trace.  What you're looking for is "does it look 'about' right?".  The measurement tools can bring along more precision than you get from the display but I wouldn't substitute a voltage reading on a scope for a reading on a DMM.  At best, the DS1054Z is a 3% kind of tool.

Watch the transistor video linked below.  Notice how the author doesn't even pretend to try for a high degree of accuracy in his measurements.  He just picks out the 'about' value and moves on.  More often than not, this is exactly how a scope is used.



The problem with the 4 vs 2 channel debate is that it is binary.  If you need 4 channels and don't have them, you have to come up with some other solution.  If you need 2 channels and have 4 channels, everything is great.

Bandwidth is the same argument on a sliding scale.  Yes, if you need 500 MHz and you only have 100 MHz, you're stuck.  But if you need 110 MHz and you have 100 MHz, you're probably still in the game.

It's like cars:  You never have too much horsepower.  OTOH, speed costs money, how fast can you afford to go?


FriedMule:
Maybe a new question can make my choice easier to make:-)

If you forget about RF and high speed digital logic. What scope would you choose for less then 1,000$
maginnovision:

--- Quote from: FriedMule on January 03, 2019, 10:09:08 pm ---Maybe a new question can make my choice easier to make:-)

If you forget about RF and high speed digital logic. What scope would you choose for less then 1,000$

--- End quote ---

micsig to1104 since you have no clue what you really want. Neither of my digital scopes was under 1k, and my analog isn't something I'd recommend to you(tektronix 475A)
David Hess:

--- 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 ---

It took a while for hardware integration and performance to reach the point where real time histograms as in DPOs (Digital Phosphor Oscilloscopes) or large sample memories were feasible.  Even today the display quality of a DSO capable of displaying an analog video signal is poor.

Personally I prefer the short record length and high acquisition rate of a DPO.  See below about waveform acquisition rate.


--- Quote from: tggzzz on January 02, 2019, 01:42:32 pm ---The early digitising scopes were awful to use, except in some circumstances. Hence the correct statement that analogue scopes were usually better.
--- End quote ---

I would say the boundary between good and useless shifted with the Tektronix 2230/2232 which were the first DSOs to support peak detection.  They lacked index graded displays but at least they could capture the envelope of a single on every acquisition.


--- Quote from: tggzzz on January 02, 2019, 06:45:20 pm ---For digital signals, the only thing that matters is the transition speed, tr; the period is completely and utterly irrelevant. The usual rule-of-thumb is that the signal bandwidth is 0.35/tr. There are a few nuances, but at this level they can be ignored.

...

Hence if you have, say, an Arduino which changes the output once per hour, and it takes 5ns to go from high to low, then the maximum bandwith in the signal is 70MHz (i.e. 0.35/5e-9) - and you scope needs to be faster than that.
--- End quote ---

This cannot be stressed enough; instead of thinking in terms of bandwidth, think in terms of transition time and the 0.35 rule:

20MHz   17.5   High Voltage CMOS
50MHz   7.0ns   Standard and LS TTL and HCMOS
100MHz   3.5ns   Fast TTL
200MHz   1.75ns   ECL

Probing above 100MHz becomes increasingly difficult.  200MHz is feasible for general troubleshooting with the shortest ground lead but higher will require a expensive active probes, low-z probes, or probe tip adapters.  If you are not prepared to deal with these, then avoid instruments above 200MHz unless you plan on only using coaxial cables.


--- Quote from: tggzzz on January 02, 2019, 07:45:37 pm ---Hobbyists frequently unwittingly create the conditions in which there are infrequent random failures or failures that take a long time to become apparent. Classic examples: failing to observe data hold times (setup times are comparatively easy), incorrect termination leading to voltage spikes which slowly damage receiver inputs, non-monotonic transitions on clock lines, ground bounce, and several others.

If present, those signal integrity problems probably won't be seen on a 20MHz scope. So when their design doesn't work as expected, people will start looking in the wrong place. Seen that far too many times!
--- End quote ---

This is the place where waveform acquisition rate matters.  A real time DSO display only requires 30fps but might take days to catch an elusive metastable event.  In practice hobbyists will have to live with whatever they can find which is pretty good today compared to just a couple decades ago even on basic instruments.


As far as the number of channels, almost all two channel instruments include a trigger input somewhat relaxing the requirement for a 4 channel oscilloscope.  But if you want to decode 3 and 4 wire serial buses like SPI, 4 channels is a great improvement.  Some low cost two channel instruments (HP?  R&S?) can now use their trigger input as a third channel for SPI decoding.
tautech:

--- Quote from: FriedMule on January 03, 2019, 10:09:08 pm ---Maybe a new question can make my choice easier to make:-)

If you forget about RF and high speed digital logic. What scope would you choose for less then 1,000$

--- End quote ---
For $1k you’re not gunna cover all bases and while your budget is more than double what the average novice is prepared invest in a new scope IMO getting a 2 GSa/s DSO is superfluous to the bulk of requirements.
rstofer and ebastler have given sound advice and I’ll add the cheaper of you two initial choices is a lot of scope for the money and I confidently state you won’t have buyers remorse.
Is something better just around the corner.....well probably but we don’t know exactly what is is just yet.
Im suspecting SDS2004X-E models but way 2ch models are priced they could be $1k+.
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