| Products > Test Equipment |
| Measuring Distortions with the Scope:What you see is not what you really have.. |
| << < (20/35) > >> |
| rf-loop:
--- Quote from: Martin72 on January 01, 2023, 04:32:33 pm ---Hi, --- Quote ---What is your SDG1000X hardware version? --- End quote --- 02-01-00-24-00 Interesting that this specification has changed so "drastically" in the last 5 years. --- End quote --- We have same HW. I also wonder what have lead to this change. I hope that some of the users who have latest HW can do comparable tests so that we can see if there have really been significant changes in this matter, or if the specification has just been changed due to some borderline case so that no one can complain under any circumstances that it does not meet the specifications. . |
| pdenisowski:
--- Quote from: rf-loop on January 01, 2023, 09:41:25 am ---Example your A1 do not measure harmonics itself at all. THis is why it do not have THD mode at all, it have only THD+N bacause its working principle and this N also include noise but also all non harmonic spurs of course... everything in band except fundamental filtered away using notch filter, if I understand its user manual right. It looks like it just measure whole all in its bandwidth just with notch filter over fundamental. So there is all, noise, all spurs and all harmonics. And example Keithley 2015 measure harmonics. Because THD. It is Total HarmonicsDistortion. If there is 2kHz signal and some spur in 5kHz. It is NOT harmonic at all. It is other tone, not part of pure THD. When someone tell just "THD" we need ask "what THD?", how measured and including what - if want avoid mess. --- End quote --- Agreed. This is how I would describe it as well: THD is only the power in the (sum of N) harmonics. The power of each harmonic is individually measured with a sufficiently narrow resolution bandwidth to minimize power from noise, spurs, etc. In this case you have to specify the fundamental frequency, the number of harmonics you want to include in the measurement, and the starting RBW (this increases in a predictable way for each harmonic, so only need to specify it for the fundamental). For THD+N, you essentially measure all power (harmonics, spurs, noise, etc.) over a bandwidth with the fundamental notched out (again, as narrowly as possible). THD+N requires that you specify the bandwidth of interest. Traditionally, THD+N was an easier measurement to make than THD, and I often see people confusing THD and THD+N. I recently did two videos on this. They are primarily focused on spec ans and RF (not AF), but the basic concepts are still the same Understanding Harmonic Distortion Measurements Measuring Harmonic Distortion with the FSW (which talks about the role of RBW) |
| Martin72:
--- Quote ---For THD+N, you essentially measure all power (harmonics, spurs, noise, etc.) --- End quote --- To me it sounds more plausible to measure everything than "only" the harmonics - Or do I have a thinking error? BTW, here is an excerpt from the service manual on how to perform the measurement(pic below). (The Googledrive link with the docs for the A1 is still active - If it´s interesting I could post it) |
| RoV:
Hi, I share also here results of a measurement I posted under the topic "Re: Siglent SDG1032X sine distortion at 1 kHz ?" Made a test on my SDG2042X (ok, 2122X ;) ). Used an E-MU 0202 connected to my PC, acquiring ~20 s at 48000 Hz sampling, 24 bit resolution. Generator at 1 kHz sine, 1 Vpp output. Acquisition gain set to have about 40% level on sin peaks. Processed with Welch method, using a Blackman window of length 4800 to minimize sidelobes and 50% overlap between data chunks: result in figure, with fundamental normalized to 0 dB. 2nd harmonic is at -103.5 dB, 3rd at -105.5. Worst is 10th at -101.9 dB. THD, computed up to the 10th harmonic, is -97.5 dBc, or 0.0013%. |
| Martin72:
Looks too fantastic... ;D Seriously, good thing. @rf-loop: Concerning thd specs of sdg1000x: I´ve read the specs of the sdg2000x, in the old sheet (2017) and in the new, a thd of 0.075% is mentioned. Same as in the specs of the sdg1000x in 2017... |
| Navigation |
| Message Index |
| Next page |
| Previous page |