Device Configuration Defaults #338
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I changed some of my device configuration settings and mistakenly did not write down what they were before I changed them. Can someone post what the default values are? I'm making some low frequency measurements 80kHz-160kHz and I'm getting a lot of noise around the center frequency of 120kHz. Trying to remove the noise and looking for suggestions. 
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Your settings are still at the default value with the exception of the PLL settling delay (default for that is 60 us). Your spike at 125 kHz is likely caused by a sub harmonic of the 2.IF at 250 kHz. You can try changing the ADC prescaler setting, this will also change your 2.IF and should move that spike to a different frequency if my assumption is correct. But you will probably not get rid of it completely. The low frequency end of the LibreVNA suffers a bit from aliasing, mixing and self-mixing of RF signals which can all lead to spikes/spurs in the S parameter measurements. There are several features in the software to try and mitigate this as good as possible but there are just too many ways some stray signals can find its way into the ADC to fully fix it. |
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Thank you so much for getting back to me so quickly. Just curious. Where are these config settings saved? I tired reloading/updating the firmware on the device, thinking that would reset them, but the settings remained the same. Maybe adding a "return to default' button in the GUI would be helpful for anyone that makes the same mistake as me. |
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The settings are stored in the flash on the VNA and are not affected by a firmware update. Things like the frequency and source/receiver calibration are stored in the same place and you usually do not want to lose them every time you update the firmware. A "return to default" button is probably a good idea and I have put it on my TODO list. |
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And now there is a "restore defaults" button in the device configuration. This functionality also required an update to the VNA firmware. If you only update the GUI, you will get an error message when trying to restore the defaults. |
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That's great. Thank you so much. |
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Your settings are still at the default value with the exception of the PLL settling delay (default for that is 60 us).
Your spike at 125 kHz is likely caused by a sub harmonic of the 2.IF at 250 kHz. You can try changing the ADC prescaler setting, this will also change your 2.IF and should move that spike to a different frequency if my assumption is correct. But you will probably not get rid of it completely.
The low frequency end of the LibreVNA suffers a bit from aliasing, mixing and self-mixing of RF signals which can all lead to spikes/spurs in the S parameter measurements. There are several features in the software to try and mitigate this as good as possible but there are just too m…