Products > Test Equipment

Show us your square wave

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EV:

--- Quote from: EV on January 28, 2015, 05:19:01 pm ---
--- 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 ?

--- End quote ---

The last picture with S-4 sampling head does not look good. So I connected the RG58 cable with 20 dB attenautor to the S-4 sampling head and here are new pictures with 5 ns and 1 ns timebase.

joeqsmith:
I tend to use a PC to control a lot of my equipment and then post post process the data with a modern PC.   

I had made a video showing some basic jitter measurements with Labview and had posted it in a LeCroy specific forum. Video can be seen here (WARNING it's pretty long and I am not real good at making videos):     


This spawned  a conversation with I assume a Teledyne sales guy about upgrading the DSOs MB.   The following is just a cut and paste to give some background: 


--- Quote ---> Imaged the drive to back it up then started over. Pretty sure anyone playing with this sort of scope
> can handle installing an OS. ha ha

Not necessarily. Not saying this applies to you but I've lost count of the number of EEs I've met that know their field inside out but are complete numbties when it comes to computers.

................

> Yes, it has 256M. Task manager does not show a lot of swapping going on even with the 256. This
> MB supports up to 2G. I added a GB and reran my tests. No gains. You may be using a lot of the > DSOs math.

In fact I do. RAM helps quite a bit (especially since you can get DDR1 sticks for next to nothing these days), but the biggest improvement comes from a faster CPU with larger cache. X-Stream does all its calculations in the CPU cache which speeds up things, but the slow 512k processors LeCroy shipped with these scopes can be a bit of a bottleneck.

> For any post processing I would typically run Labview on a modern PC anyway.

If you have LabView then this is of course an option. But you can't do real-time stuff on LabView the same way you can do on the scope.

> I may install 1Gb Ethernet and see if I can pull the data out any faster.

I doubt that. The scope's mobo has a single 33MHz PCI32 bus which is also used by the aquisition adapter (which converts the 4x Gbit Ethernet links from the acquisition board to PCI). Aside from that the max 133MB/s (theoretical, in reality it's probably closer to around 90MB/s) overall bus bandwidth which is shared across all devices and from which the acquisition system already uses a bulk of, the timing in these scopes is pretty tight so introducing another card might have some side effects.

.....

>> If you have LabView then this is of course an option. But you can't do real-time stuff on LabView
>> the same way you can do on the scope.
>
> Not sure what you mean. Real-time?

LabView needs to gather the data from the scope first, which is awfully slow compared to the X-Stream software which has access to the acquisition data in real-time. If your scope has the XDEV option then you can get around that as it allows you to build your own applications that run on the scope directly.

> > I doubt that. The scope's mobo has a single 33MHz PCI32 bus which is also used by the
> > aquisition adapter (which converts the 4x Gbit Ethernet links from the acquisition board to PCI).
> > Aside from that the max 133MB/s (theoretical, in reality it's probably closer to around 90MB/s)
> > overall bus bandwidth which is shared across all devices and from which the acquisition system
> > already uses a bulk of, the timing in these scopes is pretty tight so introducing another card
> > might have some side effects.
>
> I plan to do some benchmarking on it. Tell me more about this timing problem. Maybe you can
> save me some time.

The acquisition interface acts as a PCI busmaster. The whole processes are very timing critical. The scope is designed so that the acquisition interface has the PCI bus for its own. Introducing a Gbit Ethernet interface which will cause noticable bus loading will probably result in side effects, i.e. lowered acquisition performance, abysmal slow network performance or the scope reacting funny.

--- End quote ---

I went ahead and ran the tests and made a few videos showing the outcome.

This first video shows the DSO running non-interlaced.   


After making the first video I noticed there was a big hit in download performance when running in interlaced mode.   I played with the DSO for a while then made this second video to show the results.



I had hoped the Teledyne people would jump in to clear up my misconceptions but after making the videos they stopped posting.   

Wuerstchenhund:

--- Quote from: joeqsmith on January 29, 2015, 12:55:09 pm ---I had hoped the Teledyne people would jump in to clear up my misconceptions but after making the videos they stopped posting.

--- End quote ---

The Yahoo LeCroy forum is sparsely visited, as the low post count over the years shows (I find myself checking it maybe once a month or less), and most discussions revolve around pre-X-Stream scopes (mostly 9300 and LC Series). Don't forget that even the oldest X-Stream scope (WaveMaster 8000) is still worth some noteworthy amount of money which makes it still prohibitively expensive for most hobbyists.

Don't get me wrong, the LeCroy Yahoo forum has been a great help in the past and this on several occasions, but it's not really the place for long-winded discussions like this thread, simply because there aren't enough people spending sufficient time in it.

joeqsmith:

--- Quote from: Wuerstchenhund on January 29, 2015, 03:10:44 pm ---
--- Quote from: joeqsmith on January 29, 2015, 12:55:09 pm ---I had hoped the Teledyne people would jump in to clear up my misconceptions but after making the videos they stopped posting.

--- End quote ---

The Yahoo LeCroy forum is sparsely visited, as the low post count over the years shows (I find myself checking it maybe once a month or less), and most discussions revolve around pre-X-Stream scopes (mostly 9300 and LC Series).

--- End quote ---

Maybe the videos had nothing to do with sudden drop in responses.   If I were in sales and made a bold statement how I lost count of the number of EE's who are noobs when it comes to PCs and how making such a change was going to cause all sorts of problems, and then have a customer call me out,  I would not handle it by going silent.   

Honestly, I never did figure out what they were talking about.  I've had no problems with the 1Gb interface to date and never saw a down side to it.   

TunerSandwich:

--- Quote from: Wuerstchenhund on January 29, 2015, 12:13:22 pm ---
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.


--- End quote ---

Yes, but that is not a problem for the very specific things I use it for.  I.E. checking control signal in SMPS and other (various) low frequency DC-DC applications.  However, I would much rather see a true 12bit vertical reading, as I am not 100% sure on what levels of interpolation the ERES might be using....which obviously skews things to some degree or another. 

It has been an invaluable tool in catching over/under shoot, that normally would be missed.  I would love to see a true 12bit capture, along with a higher sample rate and some reasonable mem depth, for longer power quality captures.  That is probably my biggest complaint about the MXi I have.  It starts to lose a lot of performance and resolution/fidelity 2 long capture windows.  Obviously the PMA and other such utilities suffer because of that. 

If I expand the scope of my work (which is happening) the need for higher bandwidth, bit depth and sample-rate (plus mem) is there.  I did notice there were some trade-offs in the HDO series.  Would be nice to see LeCroy roll some technology into a single package.

I.E.
3GHz
12 bit
deep memory
industry leading sample rate
their excellent Ui/MAUI
bundle some spectral tools (with a dedicated FFT/spectrum button)
all packaged in nice form factor (which I think LeCroy does quite well) for a market leading cost
AND expand their current probe options.....
and update Wave studio (not a fan of it's interface, speed, etc...)

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