Nobody seems to be willing post anything from Rigol scopes, so I take it as the reason to assume that they are not that good.
I don't think Rigol scopes are bad, they have good reviews. Seems that people having Rigol scopes may be just busy and don't want to go into comparison with Hameg.But as I've try to point few times, I'm really interested in 10bit mode FFT screens, means that if You could turn in Your Hameg HMO scope-- HighPrecision mode ON and run FFT measurement would be very nice.
I'll try to find some time to do you an FFT. Note that you have no control over the number of bits used by the ADC. And as I say before, the ADC is probably just part of the system. For such low-level signal, you may have a preamp before the actual ADC.
Hi Rosendorfer,
Unsure what measurement you are after in FFT (dBm/dBV/Veff), bandwidth, on what signal. The Hameg does not seem to have a on/off setting for High Precision. Here's a couple of quick screenshot for a noisy 5mV 2kHz signal. The dBm/div can be turned down to 0.5dBm , but can only inspect the FFT at 5dBm / div
Hope that helps
So called high resolution and other averaging methods won't get you more bits of resolution than the ADC has.
Actually the dynamic range is determined by the ADC. Most scopes have an 8 bit ADC which could theoretically yield an FFT range of 48dB (6dB per bit -> 8*6=48). Since most ADCs are noisy, may be clocked by clocks with jitter the effective number of bits (ENOB) will be lower. In worst cases less than 6 bits which would translate in about 36dB. So called high resolution and other averaging methods won't get you more bits of resolution than the ADC has. That doesn't make FFT in a scope totally useless though. Its very handy to check filters and do a quick bandwidth check. Just don't expect a huge dynamic range like a spectrum analyser has.
Just imagine you have a comparator which can detect 2 levels and a DC level sitting somewhere. If you want to detect the DC level you'll have to add enough noise so the comparator output on average represents the DC level. This scheme has several sources of errors: the quality of the noise and the offset voltage of the comparator. A modern high speed ADC is a string of comparators each with errors which are barely small enough to make the ADC reach its specifications. You can average (oversample) what you want but the result is still loaded with errors.
Did you adjust the volt/div or magnification (zoom)?
But that still doesn't uncover how much of those extra 2 bits are real information or something that is dreamed up by the scope.
But that still doesn't uncover how much of those extra 2 bits are real information or something that is dreamed up by the scope. Using excess digits doesn't make a measurement more accurate. If a multimeter with 10% accuracy shows 1000mV then the real value can be anything between 900mW and 1100mV.
My Tek TDS744A also has a so called hi-res mode (10 bit). I set my signal generator to generate a triangle wave and made it fill the screen of the scope (first picture). Then I fed the same signal through a 40dB (100*) attenuator and set the scope to 100* magnification (second picture). Now check the differences. When the signal is magnified 100* you are looking at about 1.33 bits of the ADC. Now try to FFT that. A sine wave won't be so bad but a more complex waveform like a triangle is perfectly suitable to make imperfections visible.
Note that I used the trigger output of the generator to trigger the scope on the 2nd channel so the trigger is the same for both situations.
Hi
Can see that KedasProbe is having fun with his new scope...
Having seen HMO FFT's screens I have to say it looks very nice... ..
As per KedasProbe request for Rigol screens and to check about nctncio triangle shots,
I have spend some time with my old Rigol DS1052E and run some tests,
so KedasProbe and other HMO owners can see how nice FFT they have...
I hope it will add some practical, real life info to this discussion.
Would be perfect seeing something similar run on HMO scopes.
So There are some Triangles...My Tek TDS744A also has a so called hi-res mode (10 bit). I set my signal generator to generate a triangle wave and made it fill the screen of the scope (first picture). Then I fed the same signal through a 40dB (100*) attenuator and set the scope to 100* magnification (second picture). Now check the differences. When the signal is magnified 100* you are looking at about 1.33 bits of the ADC. Now try to FFT that. A sine wave won't be so bad but a more complex waveform like a triangle is perfectly suitable to make imperfections visible.
Note that I used the trigger output of the generator to trigger the scope on the 2nd channel so the trigger is the same for both situations.
So there are Triangles @10kHz run from Siglent SDG1025..
Screens are with Rigol FFT option set for full screen and markers @dBVrms .
First "full screen" Triangle @ 200mV/div that goes about 1,5V p-p.
then just FFT screen at 10kHz/div , so You can see just FFT more clearly.
Then 100 times attenuation that is 15mV @ 2mV/div
And again just FFT screen @ 10kHz/div and second FFT @ 25kHz/div so You can see that there is no distortion or any problems till about 300kHz. Everything looks nice and smooth as expected.
Wonder what is at nctnico screens.?
I went even bit further..
to.. 5mV p-p triangle..and even to..1mV p-p.
That are special shots for guys that are complaining at DS1052E scope noise...
Still all looks nice and smooth ...
So hope it is pretty safe to say that SFDR or dynamic range at THE CHIPEST RIGOL scope seems to be at list about 60dB.
And second is that FFT noise floor at THE CHIPEST RIGOL scope is about 108-110dBVrms.
You really need a book on how accuracy affects your measurement results The scope screen starts at approx -45dbV and ends with approx -110dBV with a noise floor at approx -100dB. The effective range is about 55dBV. You should check whether the harmonics have the expected values.