Sense spectrum by

Hi All,

I am using 1400M 2000M -F 512 -d 16 --tune-delay
–dwell-delay 10e-3 to sense the spectrum.

In main_loop(tb), I print m.center_freq and
freq_step = 0.75 * usrp_rate=0.75*(64M/16)=3M. So
m.center_freq[0]=1401.5M,[0][511] are 512 bins corresponding to m.center_freq[0];
m.center_freq[1]=1404.5M,[0][511] are 2nd 512 bins
corresponding to m.center_freq[1], and so on.

There are some comment lines say:
# are the mag_squared of the fft output (they are in the
# standard order. I.e., bin 0 == DC.)
# You’ll probably want to do the equivalent of “fftshift” on
# m.raw_data is a string that contains the binary floats.
# You could write this as binary to a file.

So actually, for each 512 bins, ([0]) to ([255]) are
values for ([0]) to ([0] +freq_step/2), and
([256]) to
([511]) are mag_squared values for ([0]-freq_step/2) to
([0]). Am I right? How to use fftshift here? Dose
give me regular order? Are fftshift( mag_squared values
to [([0]-freq_step/2):([0]+freq_step/2)]?

If I plot all or fftshift( versus all the m.center_freq
1400M to 2000M, I should get the whole spectrum from 1400M upto 2000M.
Did I
do right here? Can I get time domain signal if I do ifft( I
not. Because are mag_squared rather than mag. If not, how can I
the time-domain signal before fft, from 1400M to 2000M?


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