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vrf Moving Traces between Windows on PNA

Question asked by Dr_joel Employee on Feb 5, 2003
Axel,

The instantaneous frequency (in Hz) of a waveform is defined as ( time derivative of the phase of the complex evelope)/2*pi. To get the imaginary part of the complex envelope, take your real signal and apply a 90 degree phase shift by running it through
an fft, zero out the first and last points and multiply the rest by -j (use the function -j(1)). Then do an ifft. The result is the imaginary part of the complex envelope. You can extract the phase with the phase() function, but this will wrap the phase
into the interval -pi to pi. It's probably easiest to just go ahead and take the first difference of the result and then use the round() function to remove the resulting spikes. As usual, the devil is in the details, so you may need some zero padding,
filtering, or windowing to avoid excessive numerical noise.

--
Bill Ossmann
Philips Ultrasound
e-mail:  bill.ossmann@philips.com





                                                   To:   "VEE vrf" <vrf@it.lists.it.agilent.com>
                                                   cc:   (bcc: Bill Ossmann/ANR/MS/PHILIPS)
                                                   Subject:    [vrf] How to measure frequency

               a.kieser@francotyp.com              Classification:

               02/06/2003 06:21 AM
               Please respond to
               a.kieser






Hi there,
is there an efficient way in VEE to transform a periodical signal with
changing periods (e.g. a sound between 1kHz and 3kHz) into an f-t (frequency
vs. time) or dt-t (period time vs. time) diagram?

Thank you for your answers in advance,

With best regards,
Axel Kieser



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