Is it energy or power or neither?

[FRANCLI]

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 :)

 

[tedbradly]

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.

 

[FRANCLI]

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

 

[tedbradly]

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.

 

[FRANCLI]

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.

 

[jashua]

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).