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| Rigol DHO800 memory depth / bandwidth upgrades and noise level! |
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| ebastler:
--- Quote from: Fungus on November 06, 2023, 06:57:04 pm ---The results are in. Here's the RMS noise level of both bandwidth options, with and without bandwidth limiter, nothing connected to the inputs. There's surprisingly little difference, only about 5%. I repeated it three times just to be sure, I honestly expected more. --- End quote --- The lack of difference might be due to the fact that decimated screen data are used for the RMS calculation? (I.e. the decimation acts as another bandpass filter.) How do the results change if you change the timebase? Also, doesn't the vertical amplification go up to 500 µV/div -- does that change the result? |
| iMo:
Store the data in the .csv and make the rms calc in the excel, for example. The 40uV rms noise means aprox 270uVpp - that is what you should see on the screen then.. Also to measure noise with the open inputs is not the best approach, imho. |
| voltsandjolts:
Floating inputs are random number generators, use 50 Ohm termination. |
| 2N3055:
You cannot measure noise on 1µs/div. You are high-pass filtering low frequencies out. Pretty much all of the 1/f noise which is actually large part of noise in scope amps.. Set scope at 1 ms/div, 1mv/div, and NO 20 MHz BW limiter. To see what is actual noise with 100 MHz BW. Then repeat with 20 MHz limit. And if you look at your stats, you have very large difference between max and min AC RMS value. This is the point where you reset stats and see again. If you again accumulate have such a large difference between max and min AC RMS something is wrong. Make sure to put a non shorting cap (or wrap a piece of aluminium foil over BNC) on input so there is not induced voltage. Shorting input with 50 Ω is not going to show what noise is with 1MΩ inputs but less, which is not what you going to see with passive probes connected. Whenever i have shown any data from any scope that is how it's done. 50Ω measurements are separate set of data. If you still have large excursions in AC RMS, maybe you have some popcorn noise or something.. Or EMC problem. |
| 2N3055:
--- Quote from: ebastler on November 06, 2023, 07:33:40 pm --- --- Quote from: Fungus on November 06, 2023, 06:57:04 pm ---The results are in. Here's the RMS noise level of both bandwidth options, with and without bandwidth limiter, nothing connected to the inputs. There's surprisingly little difference, only about 5%. I repeated it three times just to be sure, I honestly expected more. --- End quote --- The lack of difference might be due to the fact that decimated screen data are used for the RMS calculation? (I.e. the decimation acts as another bandpass filter.) How do the results change if you change the timebase? Also, doesn't the vertical amplification go up to 500 µV/div -- does that change the result? --- End quote --- [4]: 500 μV/div is a magnification of 1 mV/div setting. For vertical accuracy calculations, use full scale of 8 mV. |
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