Question regarding usrp_fft.py

GNU Radio
1

Good day to all,

i have some question regarding the y-axis in usrp_fft.py… it is
labeled
in unit dB. so how does it convert from ADC value to dB? the output from
after c2mag block we got the magnitude value of the power isn’t it? so
how
does from the ADC value it convert to the power? what is the formula?

second, what is this formula mean?
log = gr.nlog10_ff(10, self.fft_size,
-20math.log10(self.fft_size)-10math.log10(power/self.fft_size)). i
think
this is to convert from power in magnitude domain to dB… is it? what is
the
actual formula on this? thank you very much in advance

Adib

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2

one more question, if the y-axis is in dB so this picture show the
reading of
around -42dB… this reading is taken without any transmission in 2.5G
channel which mean it is the reading of noise level. so isn’t -42dB is
very
high for noise? thanks

http://www.nabble.com/file/p24440598/noise%2Bpower%2Bmeasurement%2Bin%2B2.5GHz.png
noise+power+measurement+in+2.5GHz.png

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