Frequency Analysis

Forum for discussing PicoScope version 6 (non-automotive version)
Post Reply
Peter_Clements
Newbie
Posts: 0
Joined: Wed Sep 02, 2020 11:38 am

Frequency Analysis

Post by Peter_Clements »

Dear Support,

I have a Picoscope 5444D MSO bought a couple of months ago and I terminated all 4 inputs with 50R terminators.

In Spectrum Mode, I observe the images below.
I did not made any calculations, but from the images I have the feeling that there might be a correlation somehow in the positions of the peaks. The Picoscope is powered with the external PS and connected to my laptop - also powered with an external PS. I noted in the past that some peaks (especially 50Hz in Europe) went away by disconnecting both PS, but that is not the case this time.

I checked if updates where available and I have the following setup:
PicoScope® 6 - PC Oscilloscope software version: 6.14.23.5207
Model: PicoScope 5444D MSO
USB Version: 2.0
Calibration Date: 16 July 2019
Hardware Version: 1
Driver Version: 2.1.40.2131
Firmware Version: 1.7.15.0 / 1.2.34.0

Looking forward to your reply and thank you very much,
Best,
Peter
Attachments
16MHz.png
9MHz.png
5MHz.png
2MHz.png
1MHz.png
0.2MHz.png

Gerry
PICO STAFF
PICO STAFF
Posts: 734
Joined: Mon Aug 11, 2014 11:14 am

Re: Frequency Analysis

Post by Gerry »

Hi Peter,

As you haven't posted a data file, I have created one according to your setup, to comment on.

If you look at the data file and Images below you can see that the Lowest peak is falling from DC. The plotted results of an FFT transformation have very poor DC accuracy, so this is to be expected. (You could also get 50Hz peaks bleeding into the display from a connected PSU, but not at a high enough level to cause a problem, unless you're not taking the usual necessary precautions).
Spectrum peaks.psdata
(615.08 KiB) Downloaded 13 times
Low peak - Zoomed in.png

There is indeed a correlation between the other peaks. The Mid and High peaks are just biproducts of the sampling process (they are 6.25MHz and 12.5MHz respectively which is 1/5, and 2/5 of the 31.25Mhz sample rate). The peaks are below -100dBu (as yours also appear to be) which is well below the Sprurious Free Dynamic Range that we quote in our specifications of −60 dB at 100 kHz full scale input, for 8-bit mode. So, yours are not going to be significant with any signal harmonics down to about 90dBu.
Mid Peak - Zoomed in.png
High Peak - Zoomed in.png

Regards,

Gerry
Gerry
Technical Specialist

Peter_Clements
Newbie
Posts: 0
Joined: Wed Sep 02, 2020 11:38 am

Re: Frequency Analysis

Post by Peter_Clements »

Hi Gerry,
Thanks for the information, that confirms my thoughts.
Have a nice afternoon,
Best,
Peter

Post Reply