Bode plotter: huge distortions at certain frequencies

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mark_dammer
Posts: 2
Joined: Sat Apr 07, 2018 7:49 pm

Bode plotter: huge distortions at certain frequencies

Post by mark_dammer » Sat Dec 29, 2018 3:54 pm

I notice that the Bode plot is showing crazy results at certain frequency ranges. Using the standard calibration setup I am getting jumping amplitude and phase at these ranges (see attached plot):
17 - 27 MHz
47 - 51 MHz
53 - 56 MHz
Is this known behaviour and are there any workarounds for this problem ?
I tried both the Bode plotter app that come with the RedPitaya and the one on the Marketplace. Both show the same distortions.
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redpitaya
Site Admin
Posts: 387
Joined: Wed Mar 26, 2014 7:04 pm

Re: Bode plotter: huge distortions at certain frequencies

Post by redpitaya » Wed Sep 11, 2019 2:19 pm

Please give more details on what you are measuring and how.
This shows how it should look and work https://www.redpitaya.com/f136/bode-analyzer

at the same time , more details you can find in this documentation https://redpitaya.readthedocs.io/en/lat ... light=bode

It seems you might have some pins set up the wrong way, we will see.

In the case you cannot share details here, please hit me up on support@redpitaya.com

NL_Toontje
Posts: 4
Joined: Tue Oct 06, 2020 1:20 pm

Re: Bode plotter: huge distortions at certain frequencies

Post by NL_Toontje » Sat Oct 10, 2020 9:37 am

I have the same problem with the STEM 125-14 v1.0 (OS 0.99-48).
I want to measure a LPF, but when calibrating it already goes wrong.
According the manual I connect IN1, IN2 and OUT1 together with the jumpers in the LV position.
The result of the calibration run is attached as well.
What do I do wrong?

Image
Image

bma
Posts: 6
Joined: Wed Sep 23, 2020 9:54 am

Re: Bode plotter: huge distortions at certain frequencies

Post by bma » Thu Oct 22, 2020 3:50 pm

Hi,
You may have to add a 50ohm in front of the ADC.

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