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how is the dBm calculated?
Posted: Tue Aug 15, 2023 8:51 pm
by Hendrik
I'm trying to calculate the dBm of some raw IQ samples I got via gnuradio but I can't seem to find a correct link. I looked at the ADC my hackrf one uses but the IQ values don't seem to be directly related to the voltage measured. This is the formula I'm currently using but I don't know what to use for K:
avg_power = mean(I^2 + Q^2) * K / R with K as the adc scaling factor and R the resistance of the system
Re: how is the dBm calculated?
Posted: Wed Aug 16, 2023 10:31 pm
by jdow
It holds finger to wind and makes a guess based on mumbo-jumbo that sort of works.
Um, can you tell I've tried this issue before? Not gonna change.
{^_-} Incidentally, in digital terms there is no "R" in the system. Figure it's 1.0 and jigger K.
Re: how is the dBm calculated?
Posted: Tue Sep 12, 2023 4:16 am
by wallerjr
Do you still require an answer to your question ?
dbm is a power ratio relative to 1mW i.e Pdbm = 10* log(P/.001) ... P is power in watts.
As you are using a complex number (I+iQ) to obtain the power in watts V^2/R one must square the complex voltage ie. (V*conj(V))/R or { (I+iQ)*(I-iQ) } / R . This power may be averaged over however many samples you choose.
I hope that this is of use.
Jerry.