# Gain Calibration for WX FFT

**URL:** <https://www.ruby-forum.com/t/gain-calibration-for-wx-fft/231105>\
**Category:** GNU Radio\
**Created:** [July 21, 2014, 9:46pm UTC](https://www.ruby-forum.com/t/gain-calibration-for-wx-fft/231105 "2014-07-21T21:46:24Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\
**Post date:** [July 21, 2014, 9:46pm UTC](https://www.ruby-forum.com/t/gain-calibration-for-wx-fft/231105/1 "2014-07-21T21:46:24Z")

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Hello All,

I am using the USRP B210 to analyze the signal spectrum. I have  
configured it to have a 30 MHz bandwidth and the signal looks pretty  
clean. I am trying to get the GUI to present the same signal levels as  
the spectrum analyzer that I have connected to the same antenna (via  
3dB splitter). The difference between the noise floor level and the peak  
of the signal is the same on both displays, but the signal levels  
presented on the GUI are about 50 dB below where they are on the actual  
analyzer. I should also mention that I am using UHD’s rx\_samples\_to\_file  
example to save the spectrum to a file in order to use the file source  
in GNU Radio. I have attempted to raise the gain using gain argument in  
the UHD example, but the most I could achieve was about 30 dB… Is  
there anyway to calibrate the WX GUI with a software gain that makes it  
appear 50 dB stronger? I have tried using the AGC block, but after doing  
some research I’ve come to the conclusion that this acts as a gain  
regulator to a predetermined reference level, and my application does  
not have a predetermined level to aim for… Am I wrong about this? If  
not, is there any other way to apply a software gain to the entire  
signal so that both the GUI and analyzer present the same levels? Please  
let me know if any of this is unclear and thanks ahead of time!

Regards,

Michael Horvat