When making frequency domain to time domain signal what is the best procedure to get the sampling time from the frequency range?

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Sazid Hasan 2021-7-14

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评论： Walter Roberson 2021-7-14

I have a 16*16*751 matrix signal and the frequency range is from .5GHz to 2 GHz. I convert the signal from freqency domain to time domain using IFFTSHIFT(IFFT(x(f))). Now, I need the time samples for this converted signals.

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Star Strider 2021-7-14

Getting the sampling time from the Fourier transform is only possible if you know that the maximum frequency is the Nyquist frequency. The sampling frequency is two times that, and the sampling time is the inverse of the sampling frequency.

If you do not know with absolute certainty that the highest frequency of the Fourier traqnsform is the Nyquist frequency, the sampling interval will forever remain a mystery.

Sazid Hasan 2021-7-14

Thank you very much for your Answer. I would like to know if the highest frequency is 2 GHz and lowest frequency is .5 GHz and what will be the time interval and also how to calculate the starting time to end time from that freqency values?

Thank you very much.

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Answer 1

Walter Roberson 2021-7-14

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The frequency domain signal has 751 entries. Assuming the first entry is the DC component, then that leaves 750 entries for frequencies, half positive frequencies and half negative. So 750/2 = 375 frequency bins, covering 2 GHz, gives

format long g
2e9/375
ans = 
          5333333.33333333

hertz per bin, or

375 / 2e9
ans = 
                 1.875e-07

seconds per sample.

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Sazid Hasan 2021-7-14

if I take signals half for for positive and half for negative, time values will be linspace(-t,t,751). Am i correct? and if i take for both postivite and negative values, do i need to use IFFTSHIFT?