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When using SM200B, I tried to receive signals below 100 MHz transmitted from a signal generator through the API, and verified the received power with Spike. Then use FFT to calculate signal power.
I found that the signal power received via the API was much weaker than the transmitted signal, while Spike showed the signal power as normal. However, when I transmitted higher-frequency signals,like 500MHz、1GHz, both the API and Spike reported the received signal power correctly.
I also tried smgetIQcorrection() function but it didn’t work, so is there any solution for me to deal with this problem?mmark,
There are a couple scaling factors you might need to consider when FFT’ing the I/Q data from our API.
– If you are requesting 16-bit I/Q data from our API, and you want to measure dBm, then you will need to get the I/Q correction and apply it via the equations in our API manual. If you are requested 32-bit floating point data (recommended), then the data is already scaled.
– The FFT itself. I would recommend scaling the Fwd FFT by N. What additional scaling you need to apply is dependent on which FFT library you are using. Some use scaling by default, some dont.
– If you are using a window function, you want to normalize the window before windowing the data.
– Once you have the above resolved, the output of the FFT can be converted to dBm using the equation
10*log10(I^2 + Q^2)
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