Products > Test Equipment
Measuring Distortions with the Scope:What you see is not what you really have..
rf-loop:
--- Quote from: Martin72 on December 31, 2022, 06:48:04 pm ---
The data sheet of the SDG1000X series gives a THD of 0.075% (10Hz...20Khz), the measured values are significantly lower.
--- End quote ---
SDG1000X_DataSheet_DS0201X_E01I:
--- Quote ---Total Harmonic Distortion Max 0.15 % 0 dBm, 10 Hz ~ 20 kHz
--- End quote ---
Note that Min or Typical is not listed, only Max.
Example I have not at all tested all frequencies between 10Hz to 20kHz.
And then in datasheet introduction and advertising text:
--- Quote ---With 0 dBm output, the THD (Total Harmonic
Distortion) is less than 0.15%. Harmonics and
spurs are less than -40 dBc throughout the entire
bandwidth.
--- End quote ---
0.15% is specified only up to 20kHz!
Some may read this text so that 0.15% is also for entire badwith, if not calculate what this -40dBc mean.
Example if look harmonics levels graph there can find that 60MHz have THD roughly 0.75% if look (only) 2nd and 3th levels alone.
If look again this image and there 100kHz 2nd and 3th levels it give roughly ~0.05%
But then, there is also some source for mess when we talk about THD.
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.
There can also be some filters, as example Flat aka NONE and then C, CCIR A, CCITT, CCIR ARM etc but these available in Keithley.
With every setup I get different result. Also depending what all harmonics are counted. (Meters like A1 can not select harmonics at all. It can not measure harmonics, lt looks like it measure only just whole all in band. (explained in its manual)
Then, example Keithley have level ranges 100mV, 1V, 10V etc. Result also depends if test signal is near used range full scale or near bottom before lower range. (bit same as with SDG voltage bands behavior relative to THD)
Keithley specification say 0.004% residual distortion for THD and individual harmonics. THD+N it say 0.056% (-65dBc) residual .
When someone tell just "THD" we need ask "what THD?", how measured and including what - if want avoid mess.
Btw, if I set Keithley for max harmonics up to 20kHz for 1kHz test signal and I select THD+N and filter CCIT ARM I get around same "THD" values as you. (just fast looked only with two levels)
--- Quote from: Martin72 on January 01, 2023, 01:02:18 am ---The THD specification of the A1 says nothing about the number of measured harmonics, but the measuring range is given, 20hz to 40Khz.
--- End quote ---
It is somehow told in its manual. It looks like it have nothing for measure individual harmonics. This is why it have only mode THD+N. It have different working principle. Roughly saying: It measure fundamental and measure what is total without fundamental in measuring bandwidth. THD+N, so it measure all harmonics distortion and added with (+N) all non harmonics and noise in band.
If I set signal 1kHz and level SDG1000X voltage band IV top level (3.978dBm)
Then Keithley for THD+N, harmonics up to 20th and No filter aka flat. 0.0355 % (100 rdgs average)
Exactly same setup but THD alone: 0.0208 %
Just for fun:
Then continue same THD alone with CCIR ARM weighting filter: 0.0518 %
Then same but THD+N with CCIR ARM weighting: 0.0565 %
Martin72:
Hi,
The A1 is an all in one audio measurement system that can also measure tape decks, not a dedicated harmonic analyzer.
And as always when you have everything in one device, sometimes something may be omitted.
But what it does, it does well.
--- Quote ---SDG1000X_DataSheet_DS0201X_E01I:
--- End quote ---
I got this here:
https://www.batronix.com/files/Siglent/Funktionsgeneratoren/SDG1000X/SDG1000X_Datasheet_EN.pdf
Where the 0.075% for 10Hz....20Khz is stated.
blurpy:
I did some THD measurements using a 24 bit audio analyzer a while ago, of the SDG2000X:
https://www.eevblog.com/forum/testgear/the-siglent-sdg2042x-thread/msg3606484/?topicseen#msg3606484
It does quite well I think.
rf-loop:
--- Quote from: Martin72 on January 01, 2023, 11:41:20 am ---Hi,
The A1 is an all in one audio measurement system that can also measure tape decks, not a dedicated harmonic analyzer.
And as always when you have everything in one device, sometimes something may be omitted.
But what it does, it does well.
--- Quote ---SDG1000X_DataSheet_DS0201X_E01I:
--- End quote ---
I got this here:
https://www.batronix.com/files/Siglent/Funktionsgeneratoren/SDG1000X/SDG1000X_Datasheet_EN.pdf
Where the 0.075% for 10Hz....20Khz is stated.
--- End quote ---
Yes A1 is nice "all in one" instrument for repair-tune-service etc audio things.
It is shame Batronix still display old obsolete data sheet from year 2017.
Even TrueArb feature is missing.
(but yes THD is there Max 0.075% for 0dBm for 10Hz to 20kHz)
I can go down to 20Hz and Keithley tell THD 0.0293 % (100 rdgs average)
And up to 16kHz if want include 3th harmonic. (bacause it have 50kHz band max for harmonics, so with 16kHz it can still calculate 2nd and 3th): Result 0.0136%
Now need note thgat my SDG1000X is old when this old datasheet have been ok.
Why Siglent have changed this THD specification to double.
What is your SDG1000X hardware version?
If some one have more new HW and have possibility to measure somehow reliable THD... plese.
I'm curious to see if something has changed that would explain the change in specs.
Martin72:
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.
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