Is it energy or power or neither?

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Discussion Overview

The discussion revolves around the classification of the signal x(t) = e^t as either a power signal or an energy signal. Participants explore the implications of calculating power and energy for this signal, questioning the definitions and characteristics of power signals in relation to infinite values.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant, Francli, questions whether the signal x(t) = e^t is truly a power signal given that their power calculation yields infinity.
  • Another participant states that a power signal can have infinite energy and that it is acceptable for a power signal to have infinite power.
  • There is a mention that a textbook defines a power signal as one with power between zero and infinity, leading to confusion about the acceptability of infinite power.
  • A participant provides a formula for calculating the power of a signal and claims that the power of x(t) = e^t is zero, asserting that it is a power signal due to its infinite energy.
  • Additionally, it is noted that some signals may not fit neatly into the categories of energy or power signals, with an example provided of x(t) = e^t u(t), where u(t) is the unit step function.

Areas of Agreement / Disagreement

Participants express differing views on the classification of the signal x(t) = e^t, particularly regarding the implications of infinite power and energy. There is no consensus on whether the signal can be definitively categorized as a power signal.

Contextual Notes

Participants reference definitions and characteristics of power and energy signals, but there are unresolved aspects regarding the implications of infinite values in calculations. The discussion highlights potential ambiguities in textbook definitions.

FRANCLI
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Is it energy or power or neither?!

Hi,
I found in one of my lectures that the signal x(t) which equals e to the power t, is a power signal but when I calculate its power it gives infinity?
So I'm asking it is really a power signal and I mad a mistake in my calculation or what?
Thanks in advance ..
FRANCLI :)
 
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FRANCLI said:
Hi,
I found in one of my lectures that the signal x(t) which equals e to the power t, is a power signal but when I calculate its power it gives infinity?
So I'm asking it is really a power signal and I mad a mistake in my calculation or what?
Thanks in advance ..
FRANCLI :)

A power signal has infinite energy, and an energy signal has finite energy. You can remember this easily by recognizing that a signal with infinite energy can have a finite power (so it is sensible to measure its characteristics with power) and a signal with finite energy has ... finite energy (so it's a comfortable choice to measure its characteristics)

edit:
Also, a power signal can have finite power, but it does not need to as you have found out through calculation.
 
Last edited:


OK, now this signal have infinite energy but as I said when I calculate its power it also gives me infinity:(
 


FRANCLI said:
OK, now this signal have infinite energy but as I said when I calculate its power it also gives me infinity:(

The answer is infinity, and that is acceptable for a power signal.
 


Oh, really :)
I didn't know that because my textbook said that the signal is a power signal if its power is between zero and infinity and there was no sign that the infinity value itself is acceptable.
 


Can you show me your calculation step by step? You are probably wrong. The power of a signal x(t) is calculated by

Px = lim (T goes to inf) [(1/T) int (-T/2 to T/2) |x(t)|^2 dt].

So, the power of x(t)=e^t is zero. Hence, x(t)=e^t is a power signal since it has infinite enegry.

However, there exist signals that are neither energy type nor power type. One example of such signals is x(t)=e^t u(t), where u(t) is the unit step function. (quoted from contemporary communication systems).
 

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