# power & energy signals

Started by April 16, 2005
```pls can any body make me understand difference between power signals &
Energy signals.
why  r random signals called power signals.

This message was sent using the Comp.DSP web interface on
www.DSPRelated.com
```
```geeez i wish the chat-room lingo would stay in the chat room.

in article VeidnVJa8dkOkfzfRVn-uw@giganews.com, shikha at

>
> 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                  rbj@audioimagination.com

"Imagination is more important than knowledge."

```
```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.

```
```"shikha" <shikhadrdo@yahoo.co.in> wrote in message
news:VeidnVJa8dkOkfzfRVn-uw@giganews.com...
>
> pls can any body make me understand difference between power signals &
> Energy signals.
> why  r random signals called power signals.
>

Well, first of all, this is the first time I can recall ever hearing of
signals labeled like this.  So, I would suspect the labeling "energy
signals" and "power signals".  Signals are signals as functions are
functions as sequences are sequences.  But maybe I've missed something along
the way.

Robert suggested something in adding "finite" to his definitions.  Now
that
changes things a lot!   Mind well.

Oh darn!  Now I find that folks have been using these terms.  Here is one
from Stanford at:
http://www.stanford.edu/class/ee179/lecture7.pdf

VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV
1. Energy and Power Signals

An energy signal x(t) has 0 < E < 1 for average energy

inf
E = int[|x(t)|^2]dt
-inf

A power signal x(t) has 0 < P < 1 for average power

inf
P = lim [1/2T]*int[|x(t)|^2]dt
T>inf      -inf

- Can think of average power as average energy/time.

- An energy signal has zero average power. A power signal has infinite
average energy.
Power signals are generally not integrable so don&#2013266066;t necessarily have
a
Fourier transform.

- We use power spectral density to characterize power signals that
don&#2013266066;t
have a Fourier
transform.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Oh my ... and where did those 1's come from?  I guess I'd have to do a bit
of studying on this because it doesn't make any sense to me right off.  I
see an equation for E that doesn't involve time - OK.  Then I read a
description that says "average".
I always thought that power was energy per unit time.  Now we have "average
power as average energy/time"  Well the two aren't exactly inconsistent but
power=energy per unit time is already an expression of an average isn't it?
So now we have?:

average power is average average energy???  For this to be the case, there
have to be two time frames otherwise average average energy (aae) is what?

aae=[1/T]*sum[(1/T)*sum|x(t)|^2] or [1/T^2]*sumsum[|x(t)|^2]
T         T                       T  T

I'm supposed to know better than to waste time on silly things.

Here's another description from:
http://www.signal.uu.se/Courses/CourseDirs/ModDemKod/2005/Lectures/lecture1/slides.ppt#14

A signal is an "energy signal" if, and only if, it has nonzero but finite

energy for all time 0<Ex<inf:

T/2               inf
Ex =lim   int[|x(t)|^2]dt = int[|x(t)|^2]dt
T>inf -T/2             -inf

A signal is a "power signal" if, and only if, it has finite but nonzero
power for all time 0 < Px < inf:
T/2
Px =lim   (1/T)int[|x(t)|^2]dt
T>inf     -T/2

General rule: Periodic and random signals are power signals. Signals that
are both deterministic and non-periodic are energy signals.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

It seems this is supposed to help when looking at the autocorrelation and
spectral densities.  So, OK.

I learned something, I hope Shikha did too!

Fred

```
```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.

...

Jerry
--
Engineering is the art of making what you want from things you can get.
&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
```
```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
--
Engineering is the art of making what you want from things you can get.
&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
```
```"Jerry Avins" <jya@ieee.org> wrote in message
news:ieKdndZsCawKcf7fRVn-ug@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

```
```Jerry Avins <jya@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
randy.yates@sonyericsson.com, 919-472-1124
```
```Jerry Avins <jya@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
randy.yates@sonyericsson.com, 919-472-1124
```
```Fred Marshall wrote:
> "Jerry Avins" <jya@ieee.org> wrote in message
> news:ieKdndZsCawKcf7fRVn-ug@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,

I was questioning the quotes, not you. A sinusoid is sometimes positive,
sometimes negative. At the instant of transition, it is zero, violating
the condition "finite but nonzero power for all time".

Jerry
--
Engineering is the art of making what you want from things you can get.
&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
```
```On Wed, 20 Apr 2005 13:02:47 -0400, Jim Thomas <jthomas@bittware.com>
wrote:

>Jerry Avins wrote:
>> I was reversing the direction of a three-phase motor, and I
>
>[snip]
>
>Motor-direction-reversal reminds me of this conversation between Dad and
>one of his customers:
>
>Monroe: What are you doing?
>         way the motor wants to turn.
>Monroe: Well I'm surprised you didn't know this, but
>         EVERY motor turns clockwise when viewed from
>         the front.  You're wasting your time!
>Monroe: Sure it is!
>Monroe: Well, when the motor reverses, the other end
>         becomes the front!
>
>--
>Jim Thomas            Principal Applications Engineer  Bittware, Inc

Hi Jim,

Ha ha ha.  That made me laugh out loud.
Thanks, I needed that.

[-Rick-]

```
```"Jerry Avins" <jya@ieee.org> wrote in message
news:OuCdnb_fOamQ4PvfRVn-oA@rcn.net...
> Jim Thomas wrote:
>
> More power to those guys! (and I hope, no more power to me). I was
> reversing the direction of a three-phase motor, and I thought I had killed
> the power to the switch-box that controlled it. I had not. During the
> course of my exertions, I got zapped with 440 volts from thumb to thumb. I
> landed on the concrete floor about 12 feet from where I had been standing.
> My ass and left shoulder were sore from the landing, and I had a bruise on
> my chin where a knee had hit it, but no burns.
>
> Jerry
> --

Jerry,

You were undoubtedly lucky!
When I was young and in ham radio I couldn't initially afford an
electrically actuated T/R switch so I rigged up a DPDT open knife switch and
fastened it to the table top.
This was reasonably OK for CW because there was no transmitter power unless
the key was down.
Then I switched to AM.
The normal procedure was:
Switch would be in the receive position.
Listen.
Decide to transmit.
Switch to transmit position.
Turn on transmitter.
Talk.
Decide to listen.
Turn off transmitter.
Listen.

Fine.  Except a couple of times this happened (yes 2!):

Turn on transmitter.
Talk (with microphone in right hand)
Decide to listen.
[does not turn off transmitter as indicated above]
Switch to receive postion with left hand.
ZAP!  Microphone flies across the table.
RF burn on left index finger - which looks like a deep round hole about 1mm
in dia..
Shoulders / upper body got shaken pretty good.
Thank goodness the reaction got rid of the mic.

I bought a real T/R switch!

Fred

```
```Jerry Avins wrote:
> I was reversing the direction of a three-phase motor, and I

[snip]

Motor-direction-reversal reminds me of this conversation between Dad and
one of his customers:

Monroe: What are you doing?
way the motor wants to turn.
Monroe: Well I'm surprised you didn't know this, but
EVERY motor turns clockwise when viewed from
the front.  You're wasting your time!
Monroe: Sure it is!
Monroe: Well, when the motor reverses, the other end
becomes the front!

--
Jim Thomas            Principal Applications Engineer  Bittware, Inc
jthomas@bittware.com  http://www.bittware.com    (603) 226-0404 x536
Sometimes experience is the only teacher that works - Mike Rosing
```
```Jim Thomas wrote:

...

> My summer job during college was as an electrician's helper, my dad
> being the electrician.  Dad also did HVAC and appliances.  It was a
> small town, and there was another guy - Bob - who also did HVAC work.
> Bob was a great guy, and he and Dad got along famously.
>
> Bob used the same meter as Jerry's uncle - leathery fingers.  He would
> use the index and middle fingers of the same hand, touching them to the
> live wires at very nearly the same time.
>
> Dad and I were working at a house one day, and Bob and his son were
> working at the house next door.  We heard Bob yell in his distinctive
> gravelly voice, "REX!  GO GET ME THE @*#&\$^ METER!  I CAN'T TELL IF
THIS
> IS 110 OR 220!"

More power to those guys! (and I hope, no more power to me). I was
reversing the direction of a three-phase motor, and I thought I had
killed the power to the switch-box that controlled it. I had not. During
the course of my exertions, I got zapped with 440 volts from thumb to
thumb. I landed on the concrete floor about 12 feet from where I had
been standing. My ass and left shoulder were sore from the landing, and
I had a bruise on my chin where a knee had hit it, but no burns.

Jerry
--
Engineering is the art of making what you want from things you can get.
&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
```
```Jerry Avins wrote:
> About wet fingers: I used to help my uncle moonlight wiring houses. He
> must have had leather fingers. He would test a light socket by sticking
> his finger into it. Sometimes he couldn't tell, so he would wet the
> finger.

My summer job during college was as an electrician's helper, my dad
being the electrician.  Dad also did HVAC and appliances.  It was a
small town, and there was another guy - Bob - who also did HVAC work.
Bob was a great guy, and he and Dad got along famously.

Bob used the same meter as Jerry's uncle - leathery fingers.  He would
use the index and middle fingers of the same hand, touching them to the
live wires at very nearly the same time.

Dad and I were working at a house one day, and Bob and his son were
working at the house next door.  We heard Bob yell in his distinctive
gravelly voice, "REX!  GO GET ME THE @*#&\$^ METER!  I CAN'T TELL IF THIS
IS 110 OR 220!"

--
Jim Thomas            Principal Applications Engineer  Bittware, Inc
jthomas@bittware.com  http://www.bittware.com    (603) 226-0404 x536
Sometimes experience is the only teacher that works - Mike Rosing
```
```Good story, Jerry!  No sense of touch or sight, huh?  Wow, that must be tough!

"Jerry Avins" <jya@ieee.org> wrote in message
news:NMydna6qBYeGHfnfRVn-hQ@rcn.net...
> About wet fingers: I used to help my uncle moonlight wiring houses. He
> must have had leather fingers. He would test a light socket by sticking
> his finger into it. Sometimes he couldn't tell, so he would wet the
> finger. Once, he asked me to test a socket for him because he wasn't
> sure. I refused. He was odd in another respect, driving nails in light
> so dim I couldn't see the nail. He claimed that he couldn't see the nail
> in any light, so it didn't matter.

```
```Fred Marshall wrote:

...

> Really, whenever have you considered a sinusoid to possibly be of zero
> power?
> I'll just wet my finger and touch the "mains" when the power is zero
and
> .......
> oops, I'm not fast enough.  My unit of time was too long!  :-)  or =|:-o

Knowing what meaning must have been intended doesn't make the expression
of that meaning accurate. What is fine in conversation -- even via
usenet -- isn't rigorous enough for a textbook definition. As I wrote,
my cavil was with the expression "all time", not with you.

About wet fingers: I used to help my uncle moonlight wiring houses. He
must have had leather fingers. He would test a light socket by sticking
his finger into it. Sometimes he couldn't tell, so he would wet the
finger. Once, he asked me to test a socket for him because he wasn't
sure. I refused. He was odd in another respect, driving nails in light
so dim I couldn't see the nail. He claimed that he couldn't see the nail
in any light, so it didn't matter.

Jerry
--
Engineering is the art of making what you want from things you can get.
&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
```
```"Jerry Avins" <jya@ieee.org> wrote in message
news:NO-dncpu_arwwfnfRVn-sw@rcn.net...
> Fred Marshall wrote:
>> "Jerry Avins" <jya@ieee.org> wrote in message
>> news:ieKdndZsCawKcf7fRVn-ug@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,
>
> I was questioning the quotes, not you. A sinusoid is sometimes positive,
> sometimes negative. At the instant of transition, it is zero, violating
> the condition "finite but nonzero power for all time".
>
> Jerry

Jerry,

OK.

Well, definitions are wonderful things aren't they?  I took "nonzero power
for all time" to mean the "average energy over a unit of time" for
all time.
So, as long as the unit of time isn't zero then the sinusoid's power isn't
zero.  Normally we use integer multiples of the period for the "unit of
time" - as in rms.  But, if the unit of time is long enough the "integer
multiples" part becomes unimportant.

Really, whenever have you considered a sinusoid to possibly be of zero
power?
I'll just wet my finger and touch the "mains" when the power is zero and
.......
oops, I'm not fast enough.  My unit of time was too long!  :-)  or =|:-o

Fred

```
```Randy Yates wrote:
> Jerry Avins <jya@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."

It may be what Fred meant, but the originator of the definition needs to
be more careful or explain why not. Nitpickers of the world, unite!

Jerry
--
Engineering is the art of making what you want from things you can get.
&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
```
```Fred Marshall wrote:
> "Jerry Avins" <jya@ieee.org> wrote in message
> news:ieKdndZsCawKcf7fRVn-ug@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,

I was questioning the quotes, not you. A sinusoid is sometimes positive,
sometimes negative. At the instant of transition, it is zero, violating
the condition "finite but nonzero power for all time".

Jerry
--
Engineering is the art of making what you want from things you can get.
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```