Products > Test Equipment
Rigol DHO804 Test and Compare Thread
ebastler:
--- Quote from: Fungus on December 01, 2023, 12:57:57 pm ---It is, and you can do it in multiple windows. :)
--- End quote ---
But it still is just a color banding depending on the vertical position, right? Reminds me of those old video games with a transparent, colored screen overlay, before color monitors became affordable. 8)
Performa01:
--- Quote from: ebastler on December 01, 2023, 08:48:36 am ---The absence of averaging is clearly a gap. Makes the FFT output so much cleaner, and makes signals clearly visible that you otherwise have to guess at -- and it should be easy to implement. I think it's catching up with Rigol here that they implemented Averaging as an acquisition mode (only), not as a math function. That's a nice solution when you want to use Averaging on time-domain signals: no overhead and conveniently activated. But it means that averaging is not available post-FFT. A dedicated option would be needed there.
--- End quote ---
Average acquisition mode and/or math function are something completely different than averaging of an FFT trace.
Full featured DSOs have Average as
1. Acquisition mode, yet with reduced max. memory depth
2. Math function
3. Substitute for VBW setting of an SA for the FFT traces.
All three could be used at the same time, yet the value of this would be questionable.
The SDS1104X-E provides 1 and 3 from the list above.
--- Quote from: ebastler on December 01, 2023, 08:48:36 am ---Besides that, I am struggling with the "hardly anything can be set" complaint.
--- End quote ---
I do not know what can be set in the DHO, maybe Martin will enlighten us. Yet there are other maybe even more important things.
For instance, am I the only one who wonders how the “RBW” can always be “100” (without dimension), regardless of the window function?
From the sparse info on the screen we get that the FFT sample rate is 62.5 MSa/s. We don’t know the number of FFT points, so we can only assume it’s the same as the record length, which is displayed as 625.00 kpts. What a coincidence that the frequency step happens to be exactly 100 Hz in this case. And of course the frequency step is independent of the window function. The RBW on the other hand can be anything from 90 Hz to 380 Hz, hence the info on the FFT is not only misleading but plain wrong. Hardly a professional touch…
--- Quote from: ebastler on December 01, 2023, 08:48:36 am ---Looks like the Flat-top window function is plainly broken on the Rigol. It is just that particular window function which gives the unexpected results, right? Maybe they don't deal with the negative weights properly? Looks like a bug.
--- End quote ---
Who cares? As long as you can browse the web and play doom on it. You just need to get aware of the real priorities in T&M…
ebastler:
--- Quote from: Performa01 on December 01, 2023, 01:22:51 pm ---Average acquisition mode and/or math function are something completely different than averaging of an FFT trace.
Full featured DSOs have Average as
1. Acquisition mode, yet with reduced max. memory depth
2. Math function
3. Substitute for VBW setting of an SA for the FFT traces.
--- End quote ---
But if a Math function 2. were available which averages over successive sweeps, couldn't it be be applied to the FFT to obtain 3.?
--- Quote ---For instance, am I the only one who wonders how the “RBW” can always be “100” (without dimension), regardless of the window function?
From the sparse info on the screen we get that the FFT sample rate is 62.5 MSa/s. We don’t know the number of FFT points, so we can only assume it’s the same as the record length, which is displayed as 625.00 kpts. What a coincidence that the frequency step happens to be exactly 100 Hz in this case. And of course the frequency step is independent of the window function. The RBW on the other hand can be anything from 90 Hz to 380 Hz, hence the info on the FFT is not only misleading but plain wrong. Hardly a professional touch…
--- End quote ---
As stated in my questions to TurboTom, a few posts above, I have been wondering that too. If the only flaw in the displayed "RBW" is that it is not actually an RBW but a frequency step, I can live with that (although Rigol should fix it, of course, and add a unit while they are at it). But I did see some screenshots or videos earlier where unexpected "RBW" values were displayed, which did not seem to make sense even as a frequency step and assuming a Hz unit. Maybe Tom or Martin can shed some light onto whether and when this happens?
2N3055:
--- Quote from: ebastler on December 01, 2023, 09:53:51 am ---
--- Quote from: Martin72 on December 01, 2023, 09:44:54 am ---
--- Quote ---Besides that, I am struggling with the "hardly anything can be set" complaint.
--- End quote ---
Deepl translation error..
There is nothing to complain about in the menu operation, on the contrary, I think it is one of the most successful menu structures at the moment.
--- End quote ---
I didn't understand it as "it is hard to set anything", but as "there are not enough things which can be set". Is there something in the FFT which you would like to adjust but can't?
--- End quote ---
FFT settings:
Parameter | Factory Settings
Operation | OFF
Source | CH1
X | Span-Center
Unit | dBm/dBV
Center Frequency | 5 MHz
Frequency Range | 10 MHz
Vertical Scale | 20 dB
Offset | 0 dBV
Window Function | Hanning
Color Grade | OFF
Peak Search | OFF
Peak Number | 5
Threshold | 5.5 dBV
Excursion | 1.8 dB
Order | Amp Order
This is not FFT. This is some kind of simplified Spectrum view.
There are no settings for :
1. FFT mode : Normal, Average, Max Hold (at least)
2. Number of points/bins
3. RBW cannot be set. It is displayed in window title (which by the way is not visible if you do multiple windows, negating the benefit) and is some kind of function of timease. You twiddle timebase left and right until you like how it looks.
Problems with flattop window are not irrelevant. It is used for best amplitude accuracy, when trying to measure peaks amplitude.
Taking into account this simple cheap scope, I will not talk about markers and all the stuff connected to it.
ebastler:
--- Quote from: Martin72 on December 01, 2023, 12:51:46 pm ---
--- Quote --- Is there something in the FFT which you would like to adjust but can't?
--- End quote ---
Number of points for example, I'm used to being able to manually set the number of memory points (which are also not displayed on the rigol).
--- End quote ---
I thought that's set via the acquisition memory setting (up to 1 MPts)? Is the issue that it's not in the FFT dialog, or that the available steps are too coarse? Or does that setting not actually set the number of FFT points at all?
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