What is the meaning of positive phase in a bode plot?

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Discussion Overview

The discussion revolves around the interpretation of positive phase in a Bode plot, particularly in the context of signal relationships and phase shifts. Participants explore the implications of phase in steady-state conditions and its representation in Bode plots.

Discussion Character

  • Homework-related, Conceptual clarification, Technical explanation

Main Points Raised

  • One participant questions how an output signal can precede an input signal if phase represents their relationship.
  • Another participant acknowledges a mistake in their initial diagram and reiterates the original question regarding phase.
  • Some participants propose that the signals in question are not necessarily starting from a specific time (t=0), suggesting that the phase shift reflects a steady-state relationship between eternal sinusoids.
  • A later reply confirms the understanding that Bode plots depict steady-state behavior, which may clarify the initial confusion about phase.

Areas of Agreement / Disagreement

Participants generally agree on the steady-state nature of Bode plots, but there remains uncertainty regarding the interpretation of phase relationships in this context.

Contextual Notes

Limitations include the initial misunderstanding of the Bode plot's representation and the assumption that phase shifts can be interpreted outside of a time-based context.

kandelabr
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Homework Statement


I have a bode plot with a positive phase.

Homework Equations


this is a MATLAB code for the thing
Code:
% bode phase plot
w = logspace(1, 4, 100);
G = 100*(1+0.017i*w)./(1i.*w.*(1+0.05i.*w).*(1+0.0025i.*w).*(1+0.001i.*w));
fi = atand(imag(G)./real(G));
semilogx(w, fi); % x-axis: log(omega*j), y-axis: phase in degrees

The Attempt at a Solution


Nothing to solve, there's just one thing I don't get: if phase means "relation between input and output signal", how can output signal come before the input?
 
Last edited:
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Keep in mind that the signals being compared are not starting from some t=0. They are a depiction of some steady-state relationship between theoretically eternal sinusoids, and as such can exhibit a relative phase shift.
 
yeah, i thought this would be the explanation, and i neglected that bode plot is steady-state only.

thanks!
 

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