# How to get centre frequency of a pulse

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David Harra on 27 Jun 2022
Commented: William Rose on 29 Jun 2022
I have an A-scan coollected from a simulation. I am trying to obtaon the the centre frequency from the initial pulse and I am unsure how I would go about this. I have seen some formulas etc but I don't know how to apply this.
My A-scan looks like this
Any suggestions would be great.
Thanks
Dave :)
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### Accepted Answer

William Rose on 27 Jun 2022
@David Harra, Please share th Matlab code you used to generate the simulated signal, and share the formulas you have seen.
You can estimate the frequency of the signal in the plot as shown in the enlarged screenshot below.
Two cycles = 93 pixels = 93/486 us = 0.191, therefore 1 cycle=0.96 us, which corresponds to a frequency of 10.5 MHz. When you consider the possible inaccuracy of the "2 cycle" duration measurement, this 10.5 MHz estimate is consistent with the 10 MHz value expcted fro the figure label.
The 10 Mhz frequency is often called the carrier frquency. It is amplitude-modulated to produce a pulse. Perhaps you are seeking the "frequency" of the pulse used to modulate the signal. A short pulse may be described better by its duration that by some equivalent frequency. SInce you simulated it, you can share how you did it. Please also share exactly you mean by "center frequency".
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William Rose on 29 Jun 2022
@David Harra, OK, I'm glad you figured it out. Thank you for accepting the answer. I bet the power pectrum of the input signal was centered at 10 MHz. The power spectrum would be a delta function at 10 MHz, if it were a continuous wave. But when you shape it into a pulse, as this appears to be, you smear out the delta function somewhat. The shorter the pulse, the more the smearing out.

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