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Show us your square wave

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Rupunzell:
Tektronix 7104, 2x 7A29, 7B10 & S50 pulser with SMA to BNC direct to the 7A29 input (50 ohm).
Base line is trigger channel.




Bernice

Electro Fan:
Disclaimer:  even though I posted the original question I feel like I'm now posting really dumb commercials inside a seriously good TV program  :palm:

That said, I just tripped across the link below - it doesn't address all the end to end system issues (from the generator to the cabling to the scope) but it starts to get at the original question.  I think some of you might have read more into the original post than I intended - but that's A-OK, and I'm very happy to have stimulated the fuller discussion.

In my mind, a "strong" square wave is simply a square wave that looks very "square" - like what you try to get when adjusting a probe on a scope front panel.  And perhaps as many here have pointed out, there might not be a lot of other needs for a very square square wave. 

I don't know to what extent a computing or networking device needs a square square wave but I have to believe that although there are ways to pick out a 1 or a 0 from a relatively weak or poorly formed square wave at some point a very poorly formed square wave might confuse a receiving/decoding device.  No doubt my eyes seem to appreciate a highly square square wave more than most devices and circuits trying interpret square waves as 1s or 0s.  I guess that's a benefit of machines, they put up with workloads and conditions that people might not tolerate :)

So, again my post was about the simple observation of a square wave in a traditional or human perception/observational sense.  What drove the question was in part the fact that I've seen square waves that look more like sine waves to me from reputable equipment manufacturers who publish a spec for square waves - and at the upper end of the spec the square wave frankly looked kind of (very much) like a sine wave, at least to me.  So, I was just curious to see what people would call a square wave (at various frequencies and at various price points for generators).  Clearly I wasn't giving full consideration to the cabling and scope contributions - but it is great to see the discussion of the wider (and deeper) end to end considerations.

The article below addresses the question of "when is a square wave a square wave" - at least at an intermediate level.  I'll leave the advanced stuff to those here with more system-wide experience not to mention picosecond generators, GHz scopes - and color technologies.  :)

PS, I really enjoy this forum and I very much appreciate the fact that the pros and other senior members put up with entry level questions and comments.  There is huge amount of knowledge, experience, and good will in this forum and EEVblog overall.  You all rock in my book!  EF

http://mwrf.com/content/when-square-wave-truly-square
- this is a very good article; recommended; comments on it encouraged....

Wuerstchenhund:

--- Quote from: TunerSandwich on January 29, 2015, 03:01:43 am ---Regardless of age, that is a superior scope....it obviously doesn't have the bells and whistles etc, but 5GHz front end is 5GHz front end....and I believe you can also do 10GS/s interleaved?   I have extended mem on mine plus all options, but I think you essentially have the same, or better "horsepower" in your wavemaster. 

--- End quote ---

The Wavemaster 8k does 20GSa/s interleaved or 10GSa/s on all channels. However the processing is much slower than on your WRXi even if the latter is equipped with the standard P-M Celeron 1.3GHz only. The WM8k (as the WP7k) came with a first gen P4 Celeron 1.7GHz with 256k cache/400MHz FSB (later scopes came with 2GHz Celeron) which was already a slow processor when these scopes were new, LeCroy was pretty much skimping on the processor power in their older X-Stream scopes (it got better in recent years). Unfortunately there's also a limit on what processor upgrades these scopes can take, although one could replace the mainboard for the one that is used in the WP7kA/WM8kA (later revision of the intel D865GLC) and which can take later revisions P4 processors with 3.2GHz/800MHz and faster. Just never enable Hyperthreading on a WP7k(A) or WM8k(A), ever!

TunerSandwich:

--- Quote from: Wuerstchenhund on January 29, 2015, 06:15:43 am ---
--- Quote from: TunerSandwich on January 29, 2015, 03:01:43 am ---Regardless of age, that is a superior scope....it obviously doesn't have the bells and whistles etc, but 5GHz front end is 5GHz front end....and I believe you can also do 10GS/s interleaved?   I have extended mem on mine plus all options, but I think you essentially have the same, or better "horsepower" in your wavemaster. 

--- End quote ---

The Wavemaster 8k does 20GSa/s interleaved or 10GSa/s on all channels. However the processing is much slower than on your WRXi even if the latter is equipped with the standard P-M Celeron 1.3GHz only. The WM8k (as the WP7k) came with a first gen P4 Celeron 1.7GHz with 256k cache/400MHz FSB (later scopes came with 2GHz Celeron) which was already a slow processor when these scopes were new, LeCroy was pretty much skimping on the processor power in their older X-Stream scopes (it got better in recent years). Unfortunately there's also a limit on what processor upgrades these scopes can take, although one could replace the mainboard for the one that is used in the WP7kA/WM8kA (later revision of the intel D865GLC) and which can take later revisions P4 processors with 3.2GHz/800MHz and faster. Just never enable Hyperthreading on a WP7k(A) or WM8k(A), ever!

--- End quote ---

Although I am VERY pleased with my WR64MXi....the 20GS/s is quite compelling, even by today's standards that is "high end".  Lots of data there....probably grabbing some stuff I am missing, especially at "longer" timebase...do the WM8k's have the "ERES" capability?  I have found that to be EXTREMELY useful for the type of stuff I use my MXi for, day to day.  I can only imagine that the HDO series is a pretty big step above pseudo +3 bits.....I have really been considering getting a demo loan on an HDO8k, but am too afraid I won't be able to send it back. 

Wuerstchenhund:

--- Quote from: TunerSandwich on January 29, 2015, 07:20:11 am ---Although I am VERY pleased with my WR64MXi....the 20GS/s is quite compelling, even by today's standards that is "high end".  Lots of data there....probably grabbing some stuff I am missing, especially at "longer" timebase...do the WM8k's have the "ERES" capability?
--- End quote ---

Sure, all 'true' LeCroy scopes1at least since the early 90's when the 9300 Series came along had ERES, although if I remember right it was a software option back then.


--- Quote ---I have found that to be EXTREMELY useful for the type of stuff I use my MXi for, day to day.  I can only imagine that the HDO series is a pretty big step above pseudo +3 bits.....I have really been considering getting a demo loan on an HDO8k, but am too afraid I won't be able to send it back.

--- End quote ---

The problem with ERES is that it limits the available bandwidth, i.e. my 3GHz WP7300A goes down to 160MHz in 11bit ERES mode. Naturally the HDOs don't suffer from that problem.

But if you can I'd wait a bit as it's very likely that we'll soon see true 12bit scopes at higher bandwidths and sample rates as the HDO Series offers from LeCroy. Especially after Keysight came out with the MSO-S.

Overall I'm extremely happy with my WP7300A which as an every-day scope has now completely replaced my WR64Xi and my LT264M (which I'll probably sell on as I can't see myself really needing to use them in the near future). 20GSa/s and 48M are helpful, and LeCroy's options are really outstanding (although these older scopes lack the SPECTRUM option, but stuff like serial decode for a dozen or so standards incl stuff like USB3 and Fibre Channel, and the Serial Data Analyzer option more than make up for that). I'll guess I'll hang-on to the WP7300A until the WP7zi gets into more sane price regions, and even then very likely keep it.

1 Doesn't include the WaveAce and WaveJet Series

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