SDS800x HD vs DHO800x FFT

[cyo3fff]

Hello,

I had a DHO804 scope and I give it away thinking to replace it with something "better".
SDS824x HD seems to be the right choice but I have at least one question not answered.
It is about FFT refresh rate.
On DHO804, the FFT refresh rate was "real time" updated like a real time spectrum analyzer for at least 100MHz span with narrow RBW (1kHz or less).
Up to know I did not found a youtube or something similar to show the refresh rate of the SDS800x FFT.
Could someone having both scopes to do a demo on this topic please? Or one with SDS824x HD at least because I know what DHO804 is capable of.

Thank you.

BR,

Cristian

[Martin72]

Hi and welcome to the forum.

It is about FFT refresh rate.

And how is this measured or is it more of a belly feeling:

On DHO804, the FFT refresh rate was "real time" updated like a real time spectrum analyzer for at least 100MHz span with narrow RBW (1kHz or less).

You can also get the DHO800 to "stand still" at FFT, believe me.
As always, this depends on the settings, no matter which scope you have.
That's why I don't think the question can be answered in general terms; you can rather "pick out" a specific situation and then compare it - with a sense of proportion....

[cyo3fff]

Hi Martin72,

Thank you for welcoming me.

"And how is this measured or is it more of a belly feeling:"

Is more of a "feeling".

A test case would be:

FFT on an arbitrary signal (could be a wire as an antenna close to a dc-dc convertor or from a wave generator) with the following parameters:

start/stop frequency: 1MHz/200MHz
RBW: 10kHz (or 1kHz)
Max sample rate and number of points available for the kind of measurements
Windowing: Flattop (or else)
----------

But I prefer to see a movie not a still picture or, mathematically, how many frames/seconds the scope could achieved on this test case.
To "pass" the test (on my "feeling" criteria), the scope should have at least 30fps (just to give a "real time feeling" - like in a movie with 30fps or better).

Could you do this for me Martin72 please? It will help me a lot.

Thank you.

BR,
Cristian

[TomKatt]

If you gave away a DHO804 because you wanted something better, I'd be thinking you're aiming higher than an SDS824X HD...  This Siglent is a good scope (I have one myself), but this seems like a lot of fuss to basically just change team brands.  If FFT is that important and the DHO804 wasn't good enough, perhaps you ought to be aiming higher?

[Martin72]

Could you do this for me Martin72 please? It will help me a lot.

I no longer have an SDS800X HD.

If FFT is that important and the DHO804 wasn't good enough, perhaps you ought to be aiming higher?

The FFT function in particular is something that has been solved much better in the SDS800X HD than in the DHO800.

[cyo3fff]

If you gave away a DHO804 because you wanted something better, I'd be thinking you're aiming higher than an SDS824X HD... 

Hi TomKatt,

Thank you for your comment. Believe it or not, one of the main reason I give DHO804 away was...it smell! It has a very steep plastic smell and I think I'm a bit allergic to that cause if I leave it in the lab for few days, I can't stay there...so it was something serious for me.

By the way, do you (others) know if SDS800x smells like a plastic? I mean very bad not just as a "new plastic box"...I remember that smell was reported early after DHO800x was launched, here on this forum.

Coming back to the upgrade, I want something around 1000EUR +/- and yes, I'm interested to hear your (or other's) proposals so please do.

Thank you.

BR,

Cristian

[cyo3fff]

Hi Martin72,

"The FFT function in particular is something that has been solved much better in the SDS800X HD than in the DHO800."

As I started, first I'm interested how many frame per seconds can give SDS824x HD for say the above test case in comparison with DHO804.
So first I want to find the answer to that.
Second, can you detailed a bit your thought (above)? What is better on SDS800x than in DHO800?

On the other hand, maybe there is someone else on the list who can help me with FFT on SDS800x HD please.

Thank you.

BR,

Cristian

[KungFuJosh]

Siglent's FFT execution is well known to be superior.

However, with your budget, I would look at the 1000X HD series.

[cyo3fff]

Hello KungFuJosh,

Thank you for advice. SDS1000x HD with 4ch/200MHz is higher than 1000EUR. I don't need 10' screen, neither 50ohm input.
One of the main feature of the scope should be good and fast FFT cause I need to use it as a kind of spectrum analyzer for EMC debugging.

Coming back to my question, is there anybody with a SDS800x HD (particularly SDS824x HD) who can help me with FFT refresh rate (how many fps it has for the above test case)?

Thank you.

BR,

Cristian

[KungFuJosh]

There's no difference in hardware between the 800 series models. There's also no difference in hardware with the 1000 series models.

The SDS804X HD FFT is the same as the SDS824X HD.

[tautech]

One of the main feature of the scope should be good and fast FFT cause I need to use it as a kind of spectrum analyzer for EMC debugging.

Coming back to my question, is there anybody with a SDS800x HD (particularly SDS824x HD) who can help me with FFT refresh rate (how many fps it has for the above test case)?

Lake a proper analyzer, sweep speed is related to the settings you make.
Points, Span and Averaging settings provide speed or precision, pick your poison.

There are many examples of FFT use here:
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/


However these low cost DSO's don't provide a proper EMI mode like for example the SSA3000X Plus range which have preinstalled the many EMI standards and their respective level limits.
SSA3015X Plus is a good model for these LF analyser needs.

[Martin72]

Second, can you detailed a bit your thought (above)? What is better on SDS800x than in DHO800?

First would be the partially faulty windows of the FFT function, here a user had proven that they could be easily corrected, but actually this is Rigol's job to do this.
Secondly, the Rigol, like all Rigol models, lacks useful additional functions such as average and peak detect.
At least average should be "mandatory".
This would also be easy to solve if rigol were to attach importance to it.

Let's get back to your main concern, the measurement of "speed", the FPS.
I still don't quite know what you mean by that, as you mentioned realtime spectrum analyzers as a comparison.
This is a different technique behind it, the FFT function in a scope is, as the name suggests, a function, calculated mathematically.
This cannot be done/displayed in real time per se.
The "speed" then stands and falls with the number of points, the time base and the memory.
Just as an example, if the time base is set to 100ms/div in order to keep the RBW small, for example, an acquisition takes at least 1 second.
Then there is the calculation and finally the display of the function, i.e. either way you would be miles away from your 60fps.
If I were you, I wouldn't get stuck on that, instead I would focus on other qualities.
Nevertheless, I can make an FFT according to your specifications.

[Fungus]

Thank you for your comment. Believe it or not, one of the main reason I give DHO804 away was...it smell! It has a very steep plastic smell and I think I'm a bit allergic to that cause if I leave it in the lab for few days, I can't stay there...so it was something serious for me.

That completely goes away after a week or so.

(OKl, I left mine powered on for a week in a spare room so it was warm so YMMV but the smell definitely goes away)

No idea why they chose that plastic. Is it still the same in new ones...?

[Fungus]

Let's get back to your main concern, the measurement of "speed", the FPS.
I still don't quite know what you mean by that, as you mentioned realtime spectrum analyzers as a comparison.
This is a different technique behind it, the FFT function in a scope is, as the name suggests, a function, calculated mathematically.
This cannot be done/displayed in real time per se.

There's a big difference between doing the math 60 times a second and doing it 6 times per second.

The Rigol may have a simplified FFT but it is fast.

[cyo3fff]

The Rigol may have a simplified FFT but it is fast.

Hello Fungus,

Thank you for answering to my question or at least to try to answer briefly.

What I liked much to Rigol (DHO804) was its FFT speed and could compare it with the old 1054z which has a"joke" FFT in terms of speed! It take a loooot of time to do even a "few points" FFT therefore I cannot call it even close to "real time".
Just to align with everybody here, particularly in this case, by "real time" I mean at least 25fps or if you like, FFT calculations/second.
I know that this not "real time" such it is with a real time spectrum analyzer which can do a full span measurement in 1us or so but it is all right for my particular needs.

So, one conclusion is that for the same FFT settings, DHO804 (Rigol) is  "way faster" than SDS824x HD.
Am I getting right? Because this is one of my main concern.

Thank you.

BR,

Cristian

[cyo3fff]

That completely goes away after a week or so.

(OKl, I left mine powered on for a week in a spare room so it was warm so YMMV but the smell definitely goes away)

No idea why they chose that plastic. Is it still the same in new ones...?

In my case the smell was there, very intense (especially when the scope was turned on) after 6 month or so!
I've kept it in the solar light on a balcony with 30 degrees or higher temperature. Also I kept it running in a free space for few days in a row without luck.
So I've tried what I could to get rid of that but no luck at all.

The trouble with the smell is there is no way to know about it in advance. Simply there are no specifications for it. And if does exist, nobody can guarantee it will gone after a while.

Coming back to SDS824x HD, do you (or others) know if this scope has a similar smell (if you smell DHO804 you know what I mean by "similar smell")?

Thank you.

BR,

Cristian

[cyo3fff]

Let's get back to your main concern, the measurement of "speed", the FPS.
I still don't quite know what you mean by that, as you mentioned realtime spectrum analyzers as a comparison.

Hi Martin72,

Forget about real time or however we call it.
Let focus on what I want to find out by this post.

Say you have a certain FFT settings (you name it).
I want to know how long it will take to solve and display that FFT on both scopes (same settings), SDS824x HD and DHO804.

I hope now it is much more clear what I need.

Can you (or others) answer to this question please? If possible without arguments from theoretical point of view (no need for theme).

Thank you.

BR,

Cristian

[cyo3fff]

There are many examples of FFT use here:
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/

Hello Tautech,

Thank you for the answer.

I know the above thread. I could not see a speed comparison (how long it takes to compute and display the results) for a given FFT settings between SDS824x HD and DHO804.

If you find such post, please point me to it but please, if it is possible directly to the message, not the whole thread (with tens or hundreds of messages!)

It could be useful.

Thank you.

BR,

Cristian

[TomKatt]

It seems like FFT is the primary goal here - perhaps the solution is to purchase the appropriate test gear ie an actual Spectrum Analyzer ?

As others have pointed out, the FFT feature on entry level scopes is more of a math channel operation on the acquired signal.

[cyo3fff]

If FFT is that important and the DHO804 wasn't good enough, perhaps you ought to be aiming higher?

I'm not saying DHO804 was not good.
In fact I have pleased with its FFT speed (update speed on the screen) and I simply want to know if I can expect the same speed from SDS824x HD.
That is all.

Can you answer to this question please? You have the scope, that I want to buy it and I'm in stand by after this FFT clarification.

Thanks for help.

[tautech]

Coming back to SDS824x HD, do you (or others) know if this scope has a similar smell (if you smell DHO804 you know what I mean by "similar smell")?

SDS800X HD units I have unpacked (~12 now) have no strong lingering smell other that what you get from new electronic devices.
Certainly nothing I consider offensive.

There are many examples of FFT use here:
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/

I know the above thread. I could not see a speed comparison (how long it takes to compute and display the results) for a given FFT settings between SDS824x HD and DHO804.

If you find such post, please point me to it but please, if it is possible directly to the message, not the whole thread (with tens or hundreds of messages!)

As I have mentioned before, FFT sweep speed is related to the settings you use, just as they are for an analyzer.
Speed vs accuracy < pick your poison !
Today I may have a chance to do some tests.

[tautech]

SDS814X HD FFT
A few assorted screenshots, all showing a 400 MHz span representative of you might use for EMI work.
Signal from SDG6022X, dual tone with the principle @100 MHz.

These results are only applicable to the scope settings in use. FFT 2Mpts remained unchanged although it's auto managed by the scope. Memory depth is just what it was, didn't check.
Higher FFT sweep speeds are likely possible if one takes the trouble to optimize them.

At 200us/div and max 2Mpts FFT a sweep speed of ~1/s is obtained.
100us/div = ~2/s
50us/div = ~4/s
As we increase only timebase the sweep gets faster where at 10us/div its speed is indiscernible and at 500ns/div detail is starting to be lost without changing other settings.

Max hold and Average screenshots thrown in for good measure.

All other settings should be plain to see in screenshots.

[Fungus]

As I have mentioned before, FFT sweep speed is related to the settings you use, just as they are for an analyzer.

Yes, but one can still be slower than another.

[Fungus]

At 200us/div and max 2Mpts FFT a sweep speed of ~1/s is obtained.
100us/div = ~2/s
50us/div = ~4/s

Rigol is three or four times faster than that.

[tautech]

As I have mentioned before, FFT sweep speed is related to the settings you use, just as they are for an analyzer.

Yes, but one can still be slower than another.

Which one wise guy ?