Products > Test Equipment
Rigol HDO1000 and HDO4000 12bit oscilloscopes launched in China
markone:
--- Quote from: Njk on February 12, 2023, 01:28:41 pm ---Looks like FFT is still a toy function in any scope. It's not for measurements, it's just for reference. The values for SNR or dynamic range are not provided. The only related parameter in the spec is channel isolation, which is of 1:100. That's 40 dB, so anything on the FFT chart that is below that level (-60 dB, -100 dB, whatever) is just FYI. Accuracy is not officially specified. The most fierce debates are usually about toys :)
--- End quote ---
That's the point, if you need reliable spectrum analysis you buy a full specified spectrum analyzer, a DSO is designed to be used mainly as YT instrument, for sure the FFT implementation is not the key point when you look for a new instrument.
What make me really laugh is that in this forum we can see dozens of DSO's FFT screen with 100dB (or even more) vertical dynamic range and infinite debates spent to demonstrate that they are actual ::)
Anyhow, let's all keep in mind that the HDO1074 is available in EU for a little less than 1200 euro VAT included, it offers most of HDO4K features with a respectable 200MHz BW, 100Mpts , 2GSa/s.
This is the real bargain from this new line and there is nothing on the market that come close to it, i.e. the cheapest SDS2000X-HD cost 3 times more.
switchabl:
It looks to me like the FFT mode doesn't do real decimation after all (at least in the screenshots). The noise graphs published earlier in this thread seem to indicate that the Rigol has a bit less noise in the kHz region anyway. And it looks like it is running 1 Mpts FFT vs 512 kpts, so that is another 3 dB of processing gain. If there was real 500 MSa/s -> 5 MSa/s decimation (and not just subsampling) that should give another 20 dB and I'm not seeing that.
So I think it is still not quite clear what is happening with respect to resampling. Does the noise floor decrease if you switch acquisition mode to Hi-Res?
Btw I disagree that spectrum analysis does not matter much on an oscilloscope. The main point of having 12 bits is that you can analyze small details on large signals that you often can't see in a time-domain display. Spectrum analysis is a major part of the toolbox. I do agree that specifications lack a lot of detail compared to high-resolution options from Lecroy or R&S. But those are exactly the gaps that people are trying to fill here.
gf:
--- Quote from: switchabl on February 12, 2023, 02:59:25 pm ---And it looks like it is running 1 Mpts FFT
--- End quote ---
Indeed, basically looks like 1MPts (~5Hz bin spacing), OTOH the displayed RBW=5mHz @5MSa/sa would imply 1Gpts, which can't be true.
However, the "flattop" trace rather suggests a window size of only ~50k points (~100Hz bin spacing), zero-padded to a larger FFT size, leading to interpolation in the frequency domain then (which makes the shape of the side lobes visible). And as you already said, the main lobe is way to narrow for a flattop window. Any common window function has a main lobe width >= 2x the width of side lobes. Something is weird here.
2N3055:
--- Quote from: Njk on February 12, 2023, 01:28:41 pm ---Looks like FFT is still a toy function in any scope. It's not for measurements, it's just for reference. The values for SNR or dynamic range are not provided. The only related parameter in the spec is channel isolation, which is of 1:100. That's 40 dB, so anything on the FFT chart that is below that level (-60 dB, -100 dB, whatever) is just FYI. Accuracy is not officially specified. The most fierce debates are usually about toys :)
--- End quote ---
I think that is a bit simplified look at things..
SDS2000X HD: CH to CH
Isolation (@50Ω)
> 60 dBc, < 500 MHz
> 70 dBc, < 350 MHz
Also CH2CH isolation is relevant only if you use several channels at the same time.. With single channel not so much..
At that time only SFDR is relevant......
So it is very useful but need to be realistic what it is and what is it not...
2N3055:
--- Quote from: markone on February 12, 2023, 02:14:34 pm ---
What make me really laugh is that in this forum we can see dozens of DSO's FFT screen with 100dB (or even more) vertical dynamic range and infinite debates spent to demonstrate that they are actual ::)
--- End quote ---
A 12 bit scope cannot have 120 dB dynamic range.. But it can have -120dBm noise floor, and it can have larger than ADC dynamic range in FFT because of software gain.
Sometimes large dynamic range is not needed, good sensitivity is enough...
GPS signals are in the noise of preamp. It is literally not visible in time domain...
Using clever software techniques they extract useful signal from the noise...
Math don't lie. But it can be misapplied and misunderstood.
And I agree that it is better to be cautious and have a healthy dose of scepticism than believe in fairy tales..
But sometimes we can squeeze a bit more performance with a bit of cleverness.
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