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Show us your square wave

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TunerSandwich:




also this.....look at the timebase  ;)  where exactly is that "squarewave" coming from.....it sure as hell ain't the sigGen....I got a good laugh out of it anyhow

TunerSandwich:

--- Quote from: Pjotr on January 28, 2015, 04:05:35 pm ---
--- Quote from: TunerSandwich on January 28, 2015, 03:50:26 pm ---
kind of trying to re-enforce my earlier point, that showing square waves, even between "premium" gear is a rather pointless.....as it's very difficult to attribute exactly where the non linearities are coming from....are they induced (EM), are they processing "errors" etc etc etc....I could see one spending vast resources to produce a "perfect" square wave....only to realize it has no real practical application

 :-//


it really is turtles all the way down

--- End quote ---

Well, there is at least one turtle that benefits from a near perfect square wave source: Adjusting your high impedance HF probes as good as it gets :D

--- End quote ---

yes, no doubt about that....which I suppose has some VERY useful application.....when looking at impulse responses and the potential phase issues....touche'

EV:

--- Quote from: Teneyes on January 28, 2015, 12:39:30 am ---I see Rigol DSO displays are being posted on this thread and comments about overshoot.

--- End quote ---

Here are pictures you asked:

Generator: Rigol DG4162, sync out, 40 MHz square wave, connected straight to scope with about 1 m RG58 cable.

Scope: Tektronix R7103
1. pic: Timebase 7B15, Vertical amp 7A29, BW 1 GHz
2. pic: Timebase 7T11, Vertical amp 7S11 with sampling head S-2, BW ?
3. pic: Timebase 7T11, Vertical amp 7S11 with sampling head S-4, BW ?
           This picture does not look good.
4. pic: Timebase 7T11, Vertical amp 7S11 with sampling head S-4, BW ?
          RG58 cable is connected with 20 dB attenuator to the scope

Edit:  Pic 4 added. Pic 3 removed.

Wuerstchenhund:
I did a quick check of the Rigol DG1062z's square wave on a spectrum analyzer. There wasn't much time so I only tested 1MHz (where the square wave looks pretty ok) and 25MHz (where it's essentially shit). Cable is a new Huber & Suhner Sucoflex 100 which goes up to 18GHz. The BNC to N adapter is also Huber & Suhner, again rated to 18GHz.

The spectrum analyzer is an Agilent E7495B (actually it's a Base Station Test Set but pretty universal, I'll probably do a review at some point). The screenshots are a bit crap (light green on white background isn't nice) because I didn't check the capture settings where I guess the background can be changed to black as on the screen.

The two screenshots show nicely the various odd multiples of f0 which make the 1MHz square wave while the 25MHz "square" wave only shows two peaks.

Wuerstchenhund:

--- Quote from: TunerSandwich on January 28, 2015, 03:50:26 pm ---
--- Quote from: Wuerstchenhund on January 28, 2015, 12:46:07 pm ---It's a great tool but for this specific exercise I don't think it adds any value, and since the scope was running in RIS (ETS) mode I'm not sure the waveform that is displayed has much to do with the input signal. The picture shows noticeable variations in the waveform, which means RIS is unsuitable here.

--- End quote ---

It shows just how much the measurement device itself can influence the result....RIS + sinX interpolation + 3d persistence.....really shows just how many artifacts can be attributed to the WAY in which a device interpolates what it's being fed.....I wanted to show just how far away we can get from something "trustworthy", especially when sampling and interpolating a signal..
--- End quote ---

I know, but I thought I should highlight the RIS issue anyways to avoid that someone takes the screenshot too literally.


--- Quote ---Producing a model of a square wave, should be a very straight forward endeavor.....but everything in between that model and the way it's interpolated to the screen of a discreet device makes the whole concept quite a bit more "complicated".....in the "analog world" we live in....square waves just don't seem to want to exist.....and nature seems to like to avoid straight lines....
--- End quote ---

A perfect square wave can't exist, it's physically impossible as it assumes a indefinitely fast transition between low and high (which in this analog world is not possble). All we can get are more or less close approximations.

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