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Show us your square wave

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Kibi:
I have the results from two generators. One is a GW Instek SFG-2110 (10MHz bandwidth). The second will the from the built in wavegen function of my Agilent DSO-X 2002A (10MHz bandwidth).

First up: GW Instek SFG-2110

1MHz


5MHz, jitter is starting to creep in.


5MHz, with averaging switched on.


10MHz, at full chat now and jitter is quite bad.


10MHz, with averaging.




Next up is the DSO-X 2002A built in wavegen option. This seems to have better jitter performance, but not as good with the high frequency harmonics.

1MHz


1MHz with averaging


5MHz


5MHz with averaging


10MHz, full chat. I checked and it is still supposed to be outputting a square wave.


10MHz with averaging

TunerSandwich:

--- 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....I wish the scope had an AES/EBU input and I could lock it to an external sample clock (via word clock sync).....I would love to see how a pure digital interpolation of a synthesized signal is skewed by the scopes DSP/processing engine.....

I have a cool V.A.S.T synthesis engine here, that can build block chains of various types of modulations and sources (thanks Ray Kurzweil).  Sadly I think the d/a a/d and "analog" cable run would skew the results beyond the ability to make any solid predictions about HOW the scopes own interpolation transforms the original source.....(the synth has a digital out, but the scope doesn't have the corresponding input....I don't have the proper accessory)

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....

The real world is quite a complex place.....the virtual world is so much more simple.....shows just how far off we are of the vastness and complexity of the natural world....sometimes I step back and think we are still "living in caves"

somehow through all the muck we still manage to send 0 and 1 through global interconnection systems....most of which use far "shoddier" cabling solutions than we are displaying here (with lots of band-aids on them)....

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

TunerSandwich:

--- Quote from: joeqsmith on January 28, 2015, 04:34:36 am ---
--- Quote from: TunerSandwich on January 20, 2015, 09:16:47 am ---
--- Quote from: rf-loop on January 20, 2015, 08:32:05 am ---
Square wave is series of sinewaves


--- End quote ---

Indeed.......with a fundamental, and upper and lower order harmonics....here are two plots with a higher interpolated sample rate.....one showing the dynamic fundamentals of the center frequencies and the other showing the total roll-off of those fundamentals....

I am a bit puzzled by the topic of "show us your square wave".....too many variables between the oscillator/gen and the scope reading.....I don't think it says a hell of a lot about the quality of a sig gen, without analyzing the entire signal path

I did the plots posted using coax (properly terminated), but the results will be completely different with a more stable probing solution....and different i/o & measurement settings......to have any kind of real meaning in reality, there has to be a standard/definition of measurement parameters....

maybe I am missing the point of the question?





--- End quote ---

A saw your post some time ago.  You brought up some good points.   You stated the DSO you used for this data was a WR64MXI with 600MHz BW with a 15MHz input using coax.    I did not understand the THz FFT but thought I would try and replicate your results.

I am using my Sony AWG2041 to generate a 15MHz squareware with roughly the same amplitude as you show.  This generator has a little sharper edges.  I am using Thermax RGU-400 with SMAs torqued to 8"/lbs.   ARB uses crappy BNCs, so I have a BNC to SMA for this test.   My DSO is an older Wavemaster 8500A, 5GHz.     

As I would expect, the FFT drops like a rock well before I reach 10G.    Amazing how different the two setups behave. 





 

   

--- End quote ---

your cabling solution is vastly superior to the one I used....(I used the coax that came with the rigol 2102a/s)

In the original post the statement was put forth....use the maximum "horsepower" of your scope to display a square wave.....just trying to show how misleading that can really be.....

It is amazing how different the results are, between the two devices.....no doubt about that....I would argue that you have the superior scope for this kind of test.....?

Pjotr:

--- 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

TunerSandwich:

--- Quote from: TunerSandwich on January 23, 2015, 10:30:15 pm ---





--- End quote ---

I personally thought this was the most interesting signal i had posted....the square wave is still in there, amongst the garbage of the antenna

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