Products > Test Equipment
Measuring Distortions with the Scope:What you see is not what you really have..
2N3055:
Martin,
Try using Markers, On harmonics, and enable relative scale... Start FFT on horizontal from 500Hz to get rid of DC peak..
When using 0dBm or 0 dBV you have direct readout, but this way you can use it easily on any level..
Try varying AWG output level a bit. You will see there are sweet spots where AWG uses full DAC scale and output amplifier drive has low distortion. Play with input sensitivity of scope too... Like most SA, best distortion is not when driven full scale... There is a fine balance between a noise floor and amplifier spurs..
SDG2000 will generally have lower distortion, especially in sweet spots.
Best,
Martin72:
Hi my friend,
Can I test tomorrow(vacation), although it looks like it's not too far from what the spec sheet states.
(OK, the 2nd harmonic is a little "high" (appx 0.09%))
markone:
--- Quote from: Martin72 on December 26, 2022, 09:55:50 pm ---Hi my friend,
Can I test tomorrow(vacation), although it looks like it's not too far from what the spec sheet states.
(OK, the 2nd harmonic is a little "high" (appx 0.09%))
--- End quote ---
I would take with grain of salt averaged FFT spectrums, especially for THD and similar math, the wonderful dynamic range is only apparent, my trust ends at best at "SNR = 6.02N + 1.76dB" :)
Anyhow, here is my SDG2042X @ 1KHz - 0dBm as seen by HDO1000 :
rf-loop:
--- Quote from: markone on December 27, 2022, 01:22:52 am ---
I would take with grain of salt averaged FFT spectrums, especially for THD and similar math, the wonderful dynamic range is only apparent, my trust ends at best at "SNR = 6.02N + 1.76dB" :)
Anyhow, here is my SDG2042X @ 1KHz - 0dBm as seen by HDO1000 :
--- End quote ---
You can take what ever salt or sugar... ;)
Btw, this averaging doesn't affect the signal levels, but it does affect the noise floor, so we can peek "underneath" the noise level...(without true need here) but there we can ONLY see these signals that are in sync(!) what is sometimes very important (depending what we are doing). As long as this is true etc...... you know. Of course it works and this way we can communicate in a very simple way with radio signals that are much below the noise level, which cannot be detected at all by a normal "modern/high-end" radio. And no bystander knows that communication is taking place there (until they find how to sync and how to open messages, but how they do it if they do not know what to try find and where. ;)
https://www.analog.com/media/en/training-seminars/tutorials/MT-001.pdf
Btw, in Rigol image there is RBW: 90.90m
Where is specified what it really mean.
In your image can read that FFT samplerate is 1MSa/s and you have there 20kHz span.
With 1MSa/s normal FFT full span is 500kHz and you have then selected 0-20kHz span. If there is 1Mpts and full span is 500kHz then Delta f is 0.5Hz. But what is this RBW "90.90m"?
What is FFT window used in this image.
DHO1000 user manual or data sheet do not tell anything but "resolution".
Also in DHO1000 (HDO1000) manual: "FFT resolution is the quotient of the sample rate and the number of FFT points. If the number of FFT points is a fixed value (65,535 at most),......." :wtf:
markone:
--- Quote from: rf-loop on December 27, 2022, 09:01:53 am ---
Btw, in Rigol image there is RBW: 90.90m
Where is specified what it really mean.
In your image can read that FFT samplerate is 1MSa/s and you have there 20kHz span.
With 1MSa/s normal FFT full span is 500kHz and you have then selected 0-20kHz span. If there is 1Mpts and full span is 500kHz then Delta f is 0.5Hz. But what is this RBW "90.90m"?
What is FFT window used in this image.
DHO1000 user manual or data sheet do not tell anything but "resolution".
Also in DHO1000 (HDO1000) manual: "FFT resolution is the quotient of the sample rate and the number of FFT points. If the number of FFT points is a fixed value (65,535 at most),......." :wtf:
--- End quote ---
I can confirm, among many other, there is a bug regarding acquisition parameters display during FFT operation.
Right yesterday, when i was doing the meas that i attached in my post, i found out that rotating horizontal scale FFT acquisition sample rate, sample interval and samples number were not changing in accordance :D
Anyhow, the produced spectrum graph is "aligned" with an equivalent meas made with my SSA3021X in sweep mode, so i'm confident about that image, RBW apart for obvious reasons.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version