[sdiy] What test gear do you use?

[rsdio at audiobanshee.com]

I have never seen an Owon scope at any of my clients’ facilities, so I won’t be able to give one the ol’ Rigol test.


But you don’t need me, you can try the following for yourself:

1) Start with a circuit that has some kind of DC offset, preferably an offset that you can vary, although not necessarily continuously - two options will suffice. Maybe something with a virtual ground.

2) Connect a probe to this DC value and manually crank the gain on your ‘scope until you can measure the noise floor on that signal. You’ll need to adjust the Position to keep the signal on the screen at high gain since it’s not centered around 0 V.

3) Now, make a change to the circuit that shifts the DC bias elsewhere. With the high gain from step 2, this DC change should move the signal trace well off of the screen. Try adjusting the Position again until the signal is back in view.


With any decent ‘scope, these steps are not difficult. You intuitively change the Position knob quickly until the signal is visible somewhere on the screen, and then you slow down your adjustments and perhaps reverse direction until you get close to the desired reticle. Your adjustments will naturally get slower and slower and you make finer and finer adjustments.

With the Rigol, steps 2 and 3 can be impossible. Turning the Position knob at a medium speed seems to take forever, and the signal doesn’t ever appear on the screen. Continued adjustment eventually results in an overshoot. Slow or fast turns of the Position encoder simply do not behave as expected. There are sudden jumps in the signal on the screen. There seem to be three modes: painfully slow, ridiculously fast with overshoot, or sudden changes between the extremes. As I said, I found the Rigol to be unusable.

I’ve sent a message to my client asking what model Rigol ‘scope they have so I can find out whether it’s the same model you guys seem to love so much. My client is not exactly strapped for cash, they purchased their Rigol new, and they have not made any of the popular hacks. It’s probably a firmware design fail, or perhaps bad signal conditioning on the encoder(s') phase signals.

Brian


On May 7, 2018, at 7:52 AM, Tom Wiltshire <tom at electricdruid.net> wrote:
> Have you ever used one of the Owon scopes, Brian? Similar price to Rigols, but better than what you’re describing, if the Rigols are really that bad.
> 
> I’d be interested to hear your view. I’ve been using one for several years now and find it very suitable for the stuff I do. It’s fast and plenty accurate enough for my purposes. The interface is clear and pretty straightforward, I’d say. One or two of the lesser-used features might be a bit of a poke-around,  but that’s why they put the lesser-used features there and gave the common stuff it’s own front panel button.
> 
> I’ve never used a Tek scope, but unless it makes me toast and a nice cup of tea and magically improves my sex life, it’s going to struggle to justify the huge price-per-feature increase over cheaper scopes. Seems to me they’re mostly aiming at a market of people who buy them for the work lab with someone else’s money. I’m not convinced at all.
> 
> Tom