How to calculate Signal Power using ADC samples?

1. How to calculate Signal Power using ADC samples?

Hi, I'm going to test the performance of an antenna, but unfortunately the antenna is connected to the receiver front-end and ADC on the board and cannot be separated from the board. So the only way I can read out the signal is to read the data from ADC. Is it possible to convert voltage samples into power(in dBm)? I've seen that some ADCs are able to plot the spectrum(in dBm) using the software interface. I have very poor knowledge about ADC. What does the ADC calibration usually do? (I just heard about this function)

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2. Re: How to calculate Signal Power using ADC samples?

Hi,

An ADC just converts an analog signal into a digital signal.
You need to read the datasheet about the data format.

To get the spectrum you need:
* a known, fixed, stable sampling rate
* take 2^n samples (where n should be in integer to perform an FFT. E.g. n= 10 for 1024 samples)
* use a windowing function
* perform the FFT
* calculate the absolute (vector length) of the each output bin (real and imag part)
* do the logarithmic calculation for each output value
* do the X-Y plot

For 2^n samples you get 2^(n-1) frequency results.
The frequency step size is linear and is f_sample / 2^(n), starting with 0Hz = DC.

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For more detailed informations you need to read basic informations first. (A forum can not replace this).
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There will be software tools that help you do all the (mathematical) functions for you.
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The power can be calculated by performing an RMS calculation over the desired count of samples.

Klaus

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3. Re: How to calculate Signal Power using ADC samples?

http://www.sjsu.edu/people/burford.f...utorial_NI.pdf

NI has some good info: "According to the Nyquist criterion, the sampling frequency, Fs, must be at least twice the maximum frequency component in the signal. If this criterion is violated, a phenomenon known as aliasing occurs"
Sean

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