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Discussion Groups | Comp.DSP | power & energy signals

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power & energy signals - shikha - 2005-04-16 09:01:00

pls can any body make me understand difference between power signals &
Energy signals.
why  r random signals called power signals.

		
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Re: power & energy signals - robert bristow-johnson - 2005-04-16 11:44:00

geeez i wish the chat-room lingo would stay in the chat room.

in article V...@giganews.com, shikha at
s...@yahoo.co.in wrote on 04/16/2005 09:01:

> 
> pls can any body make me understand difference between power signals &
> Energy signals.

a finite energy signal:

                     +inf
    total energy = integral{ x(t)^2 dt}   < infinity
                     -inf


a finite power signal:

                                +T/2
    average power = lim  1/T  integral{ x(t)^2 dt}   < infinity
                   T->inf       -T/2


> why  r random signals called power signals.

because, like a sine wave, if they are left turned on forever, they will
deliver an infinite amount of energy.  but their average power is finite.

-- 

r b-j                  r...@audioimagination.com

"Imagination is more important than knowledge."


Re: power & energy signals - Manuel M - 2005-04-17 10:58:00

shikha wrote:
> pls can any body make me understand difference between power signals
&
> Energy signals.
> why  r random signals called power signals.


Trying to make it easy:

An energy signal has a finite energy. Signals of a limited length
also carry a finite energy, and so they are energy signals. A signal
that decays exponentially, for example, also has a finite energy.

A power signal is not limited in time (it is *always* on, from the
Big-Bang to Judgement Day and beyond), and has an *infinite* energy.
Since an infinite energy has no meaning for us, then we use the energy
per unit of time, i.e., power.

Examples:
A square pulse is an energy signal.
A square wave of infinite length is a power signal.


Re: power & energy signals - Fred Marshall - 2005-04-18 12:41:00



Re: power & energy signals - Jerry Avins - 2005-04-18 13:17:00



Re: power & energy signals - Jerry Avins - 2005-04-18 13:21:00



Re: power & energy signals - Fred Marshall - 2005-04-18 13:26:00

"Jerry Avins" <j...@ieee.org> wrote in message 
news:i...@rcn.net...
> Fred Marshall wrote:
>
>
>> A signal is an "energy signal" if, and only if, it has nonzero but finite 
>> energy for all time 0<Ex<inf:
>
>   ...
>
>> A signal is a "power signal" if, and only if, it has finite but nonzero 
>> power for all time 0 < Px < inf:
>
> Hunh? again. A sinusoid fits neither of those verbal descriptions.
>

Jerry,

First off, these were all "quotes" ...... and I was questioning the whole 
thing from the get go.

Second, why doesn't a sinusoid have finite but nonzero power for all time? 
er.... if I know what that even means!  Again, if power is energy per unit 
time then finite for all time (in chunks of time) seems OK to me.

Fred

Fred


Re: power & energy signals - 2005-04-18 14:10:00

Jerry Avins <j...@ieee.org> writes:

> Fred Marshall wrote:
> 
>    ...
> 
> > - An energy signal has zero average power. A power signal has
> > infinite average energy.
> 
> 
> Huh? Power goes with the square of magnitude (into a resistive
> load). It is a positive number for all non-zero magnitudes. To have
> zero average power, a signal must be brief and averaged over all time,
> or everywhere zero.

This is correct, Jerry, as I understand it. Any finite-temporal-extent 
signal is considered a finite-energy, zero-power signal because of
the first reason you stated.
-- 
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
r...@sonyericsson.com, 919-472-1124


Re: power & energy signals - 2005-04-18 14:12:00

Jerry Avins <j...@ieee.org> writes:

> Fred Marshall wrote:
> 
> 
> > A signal is an "energy signal" if, and only if, it has nonzero but
> > finite energy for all time 0<Ex<inf:
> 
> 
>    ...
> 
> > A signal is a "power signal" if, and only if, it has finite but
> > nonzero power for all time 0 < Px < inf:
> 
> 
> Hunh? again. A sinusoid fits neither of those verbal descriptions.

Why don't you think a sinusoid has finite but non-zero power? When
Fred stated "... for all time..." I'm assuming he means "when averaged
over all time."
-- 
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
r...@sonyericsson.com, 919-472-1124


Re: power & energy signals - Jerry Avins - 2005-04-18 21:18:00



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