[sdiy] Best scopes for the money, 2020?

[Jay Schwichtenberg]

I have lots of hours (thousands) on scopes, specifically Tek scopes so 
I'm biased there. I sure wouldn't mind having fully loaded Series 5 or 
MDO3K/MDO4K but those are outside my budget.

Anyways I'm a fan of digital scopes, I have 2 analog scopes that rarely 
get used any more, my Rigol 1054 works just fine for me.

With a digital scope you have:
* Buffered acquisitions and persistence (not waveform, acquisition). So 
you can trigger on something and it will still be on the screen.
* You can set the trigger point anywhere in the acquisition so you can 
look at stuff at, before or after the trigger.
* With long acquisition buffers you can trigger on something and look at 
what happened fairly far out.
* Digital measurements. No more need for counting graticule ticks and 
doing math.
* More and more things have uCs and serial buses (SPI, I2C, I2S, CAN) 
which digital scopes can decode. Sometimes looking at serial buses in 
the analog realm will help with bus contention issues.
* More stable as far as calibration (at least Tek scopes are).
* Most digital scopes have the ability to be controlled with GPIB 
commands over USB or network. Some even have websites built into them or 
PC apps so you can control them via network or USB. Want to do some 
processing of an acquisition, download it and process it on your PC.

I think there are two fields that scopes are used in. First engineering 
where they are more of a debug/troubleshooting tool and in science where 
there are more of a measurement tool. Being an engineer I view it as 
more of a debug/troubleshooting instrument. Digital scopes will be more 
accurate with time measurements than voltage measurement. Acquisitions 
(timing) are done with accurate crystal oscillators but most digital 
scopes only have 8 bit ADCs. In general if you hook a scope up to a 
circuit and measure stuff I'd say you're about 10% accurate for 
measurements. When you get in and start optimizing your measurement then 
things can get to things down to 5% and if you really know your scope 
(and it's a decent calibrated one) and tweak things further you go lower 
than that.

A good, calibrated analog scope can give better voltage readings, timing 
maybe. But the thing is those are calibrated scopes. I bet there are 
very few people here that send there scopes out annually to get 
calibrated so their measurements aren't probably up to snuff. So if you 
buy used send it out to get calibrated and if they say it's calibrated 
get the calibration certificate with it. You'll also have to add the 
calibration cost into the scope cost. Analog scopes need to get 
calibrated every year (or more) if you want to keep them accurate. 
Digital scopes still need calibration ever so often if you want accurate 
measurements. Tek DPO/MSO/MDO 2K/3K/4K scopes have factory calibration 
and user calibration. Factory calibration needs to be done at a service 
depot and user calibration I'd do weekly or even daily depending what I 
was doing. And scopes are like VCOs, let them warm up fro 30 minutes 
before you calibrate them.

Jay S.

On 12/1/2020 11:47 AM, Amos wrote:
> Hi folks,
>
> I suspect this is a group that includes folks who keep up with things 
> like, what low-end scopes have custom firmware in circulation that 
> unlocks advanced features, or what chinese off-brand DSO gives you the 
> performance of X at a cost of <<X, etc...
>
> I'm more looking for cheap and cheerful than highest-end, but Very 
> Nice scopes for merely Nice prices are relevant too.
>
> Do you have a favorite budget scope, or one you'd recommend for 
> equipping a low end lab / repair bench?  Thanks!
>
> -Amos
>
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