| Products > Test Equipment |
| Measuring Distortions with the Scope:What you see is not what you really have.. |
| << < (14/35) > >> |
| baldurn:
--- Quote from: mawyatt on December 29, 2022, 05:37:00 pm ---Edit: Added a result from our Spectrum Analyzer with a 10dB PAD in front (almost always keep a PAD on front end, saves replacing SA front ends), see PNG18. The SA amplitude hasn't been calibrated, but the relative IMD readings are good. Note the lack of artifacts and the level of the IMD Products. It's interesting that the PicoScope shows even better IMD results than the SA, a tribute to the PicoScope and of course the SDG2000X+ AWG signal source!! --- End quote --- How do we know that the extra IMD products shown on the Pico are real? |
| mawyatt:
--- Quote from: baldurn on December 29, 2022, 06:21:02 pm --- --- Quote from: mawyatt on December 29, 2022, 05:37:00 pm ---Edit: Added a result from our Spectrum Analyzer with a 10dB PAD in front (almost always keep a PAD on front end, saves replacing SA front ends), see PNG18. The SA amplitude hasn't been calibrated, but the relative IMD readings are good. Note the lack of artifacts and the level of the IMD Products. It's interesting that the PicoScope shows even better IMD results than the SA, a tribute to the PicoScope and of course the SDG2000X+ AWG signal source!! --- End quote --- How do we know that the extra IMD products shown on the Pico are real? --- End quote --- We don't, but they are lowest (~ -100dBc ref to 0dBm signal peaks, noise floor ~ -115dBm)) of the group of tests, so would baseline them as the resultant of the PS and AWG. Please note the SA doesn't show some of these artifacts, but the PS shows some that are below the SA noise floor ( ~ -103dBm, signal peaks is ~ -11dBm due to input PAD). Since we can't "assume" the PS contributed these, truth would be of course both contributed but we can't separate either, so safe assumption it's the AWG if one is looking for the signal source "quality". Of course if we only had the general purpose DSO results, then this would "paint" an entirely different picture of the AWG, since without another "good" measurement instrument we couldn't defer/question the DSO results. Please remember in engineering measurements, one is always looking for a source significantly better than the measuring instrument, this helps to "verify" that the measuring instrument is good for the task. Also applies to evaluating a DUT, where one wants the "input signal" to be significantly better than DUT, so the end resultant measurement is mostly due to the DUT effects and not the poor quality input signal (or measuring instrument). Best, |
| baldurn:
IMD is very common in receivers so I could easily see all three instruments generating those IMDs internally. Maybe generate and measure each signal independently before combining them externally using a passive power combiner. If that shows the same IMD products it should be the measuring instrument doing it. I would try it but I do not have a power combiner available. |
| mawyatt:
Agree, the resistive combiner should produce the best overall IMD from the signal various sources. However, these AWGs under discussion have a built-in combiner, whether it's digital or analog don't know, but produces a Two Tone Signal without any additional components or cables, just one cable, and produces very respectable results (better than we expected) as shown by the various previous plots. As always YMMV, Best |
| blackdog:
Hi, I did some measurements on the function generators available here in my lab. I have limited myself to the audio region at 2V RMS output at a 50 Ohm load. These THD measurements were done with Sine signals, if time is available, I will show from the generators also the square wave representation, but I will do that in a separate post. All equipment used had been on for at least 1 hour before I started measuring. These types of measurements take a fair amount of time and I have to do this in between my work. :-) The equipment used: Hameg /R&S: HMF2525 Siglent: SDG1032 Siglent: SDG2042 Rigol: DG4162 The scope used for the THD pictures is a Hameg /R&S: HMO3004 And the THD meter is an Audio Precision: Portable One Plus The spectrum picturers are made with a Siglent SDS2104 Plus First the SDG1032X 14Bit Generator This is the display of the Audio precision Analyser and it shows the measured THD at a bandwidth of 400Hz to 80KHZ, rounded off the THD is 0.07%. . This scope picture shows the measured 10KHz Sinus in the color yellow and the green trace is the residue of the Analyzer output. Do not look at the size of the green trace, this is because the analyzer output is auto scale. I only show the green trace to get an idea of what the THD looks like. . The following picture shows what the FFT looks like done with the Siglent scope. Keep in mind that the table always varies a bit, especially at the somewhat higher harmonics. Keep in mind the table value of -+1dB. ******************************************************************************************************************************** ******************************************************************************************************************************** Now the Siglent SDG2042X 16Bit Generator This is the display of the Audio Precision Analyser and it shows the measured THD at a bandwidth of 400Hz to 80KHZ, rounded off the THD is 0.007%. . This scope picture shows the measured 10KHz Sinus in the color yellow and the green trace is the residue of the Analyzer output. Do not look at the size of the green trace, this is because the analyzer output is auto scale. I only show the green trace to get an idea of what the THD looks like. . The following picture shows what the FFT looks like done with the Siglent scope. Keep in mind that the table always varies a bit, especially at the somewhat higher harmonics. Keep in mind the table value of -+1dB. ******************************************************************************************************************************** ******************************************************************************************************************************** Now the Hameg HMF2525 14Bit Generator This is the display of the Audio Precision Analyser and it shows the measured THD at a bandwidth of 400Hz to 80KHZ, rounded off the THD is 0.023%. . This scope picture shows the measured 10KHz Sinus in the color yellow and the green trace is the residue of the Analyzer output. Do not look at the size of the green trace, this is because the analyzer output is auto scale. I only show the green trace to get an idea of what the THD looks like. . The following picture shows what the FFT looks like done with the Siglent scope. Keep in mind that the table always varies a bit, especially at the somewhat higher harmonics. Keep in mind the table value of -+1dB. ******************************************************************************************************************************** ******************************************************************************************************************************** Now the Rigol DG4162 14Bit Generator This is the display of the Audio Precision Analyser and it shows the measured THD at a bandwidth of 400Hz to 80KHZ, rounded off the THD is 0.011%. . This scope picture shows the measured 10KHz Sinus in the color yellow and the green trace is the residue of the Analyzer output. Do not look at the size of the green trace, this is because the analyzer output is auto scale. I only show the green trace to get an idea of what the THD looks like. . The following picture shows what the FFT looks like done with the Siglent scope. Keep in mind that the table always varies a bit, especially at the somewhat higher harmonics. Keep in mind the table value of -+1dB. ******************************************************************************************************************************** ******************************************************************************************************************************** Now the Audio Precision: Portable One Plus - Generator Analog Generator This is the display of the Audio Precision Analyser and it shows the measured THD at a bandwidth of 400Hz to 80KHZ, rounded off the THD is 0.0008%. THD with my PC and a verry good Soundcart is about 0.0002. . This scope picture shows the measured 10KHz Sinus in the color yellow and the green trace is the residue of the Analyzer output. Do not look at the size of the green trace, this is because the analyzer output is auto scale. I only show the green trace to get an idea of what the THD looks like, this is almost all noise... . The following picture shows what the FFT looks like done with the Siglent scope. Keep in mind that the table always varies a bit, especially at the somewhat higher harmonics. Keep in mind the table value of -+1dB. . And what does the last picture, which is the FFT from de AP generator on the Siglent Scoop show us now.... The Siglent scope I used, does not have sufficient capabilities to make good FFT measurements below say 50dB. The slightly newer 12Bit Siglent series scoops will do 15 to 20dB better I think, the SDS2104X is a basic 8Bit scoop with 10Bit oversampling. Later I will show some pictures of the square wave the generators can make. Kind regards, Bram |
| Navigation |
| Message Index |
| Next page |
| Previous page |