Why the amplitude of the 90 shifted phase signal when use the analytic signal block is not equal to the original signal?

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saleh shlimet
saleh shlimet 2020-6-7
评论： Walter Roberson 2020-6-20
I could manage to shift the phase of signal by 90 by using analytic signal block. But, the problem is that its amplitude is not equal to the original one. Can anyone please explain it?
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Jyotsna Talluri
Jyotsna Talluri 2020-6-16
You can try variable phase shift block in simulink.
https://www.mathworks.com/help/simrf/ug/variable-phase-shift.html
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Walter Roberson
Walter Roberson 2020-6-20
Suppose you leave the program running for two weeks. Then a frequency as low as one cycle per week could be detected, mathematically. That frequency has to have its phase shifted by 90 degrees, just like all the other frequencies do.Is it mathematically possible for something like a hilbert transform to properly predict when to make the appropriate output adjustments before the system has seen one cycle of the wave? Nyquist would say NO.
I would argue that it is therefore not possible to do what you want in a real-time system, unless
  1. You put a lower-frequency boundary for detection (upper frequency is according to sampling frequency); and
  2. You have a transport delay corresponding to one cycle of that low frequency.

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