average signal magnitude not zero
 

Hello, thank you for reading this post.

When analysing wideband impulse signals from a wideband antenna I have
realised that the average signal magnitude is not zero. I have thought this
is because the reactance of the antenna at different frequencies varies and
since it is a wideband antenna there can be energy measured since it is only
for an extremely small period of time of 2-4 us. However, I am not sure and
would greatly appreciate the views of this newsgroup.

is this surprising? what did you expect to find, and why?? why do you
think 2-4us is a small period of time, and why does that matter?? what is
an 'impulse' signal that you are measuring?? and how do you define 'signal
magnitude??

"Galilea" wrote in message
...
Hello, thank you for reading this post.

When analysing wideband impulse signals from a wideband antenna I have
realised that the average signal magnitude is not zero. I have thought
this
is because the reactance of the antenna at different frequencies varies
and
since it is a wideband antenna there can be energy measured since it is
only
for an extremely small period of time of 2-4 us. However, I am not sure
and
would greatly appreciate the views of this newsgroup.

"Galilea" wrote in message
...
Hello, thank you for reading this post.

When analysing wideband impulse signals from a wideband antenna I have
realised that the average signal magnitude is not zero. I have thought
this
is because the reactance of the antenna at different frequencies varies
and
since it is a wideband antenna there can be energy measured since it is
only
for an extremely small period of time of 2-4 us. However, I am not sure
and
would greatly appreciate the views of this newsgroup.


Are you saying the DC value is not 0 ?

Tam/WB2TT

Tam/WB2TT wrote:
"Galilea" wrote
When analysing wideband impulse signals from a wideband antenna I have
realised that the average signal magnitude is not zero. I have thought
this
is because the reactance of the antenna at different frequencies varies
and
since it is a wideband antenna there can be energy measured since it is
only
for an extremely small period of time of 2-4 us. However, I am not sure
and
would greatly appreciate the views of this newsgroup.

Are you saying the DC value is not 0 ?

He seems to be saying the DC value is not 0 for a sampling
time period of 2-4 uS which would of course be true for a
sine wave if, e.g., an odd number of positive cycles were
sampled along with an even number of negative cycles. Or
if the frequency was lower than 250 kHz. Plus all the
signals and noise are superposed.
--
73, Cecil http://www.qsl.net/w5dxp


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First of all, my apologies. As you can gather it is the first time I post in
this newsgroup. In the process, the computer kept on telling me that I
required authentification (I had forgotten to click on one of the boxes) and
said that it could not send the message. I therefore ended up writting it
several times. As it turned out, two of the times where it told me it had
not sent it, it had. I greatly apologise for all the inconvenience.

Secondly, yes, I mean to say the signal has a DC component. I would have
thought that impulsive noise, being cause by electron movement would produce
an AC signal, otherwise where does the DC come from? The importance of the
time is because I would have thought that in the long term the antenna would
resonate so as to produce a zero mean signal (AC). Sorry, the answer might
be common sense but I just fail to see it.

Thank you for your time and once again, sorry.


"Galilea" wrote in message
...
Hello, thank you for reading this post.

When analysing wideband impulse signals from a wideband antenna I have
realised that the average signal magnitude is not zero. I have thought
this
is because the reactance of the antenna at different frequencies varies
and
since it is a wideband antenna there can be energy measured since it is
only
for an extremely small period of time of 2-4 us. However, I am not sure
and
would greatly appreciate the views of this newsgroup.

yes, a signal can have a dc component, even from a small antenna. (just
watch the arguments over this one) it gets even worse if you sample over a
short period like a few microseconds depending on the characteristics of the
signal you are measuring. and it can get much worse over a long period
because of numeric integration errors accumulating, or small measurement
bias in instrumentation accumulating.

"Galilea" wrote in message
...
First of all, my apologies. As you can gather it is the first time I post
in
this newsgroup. In the process, the computer kept on telling me that I
required authentification (I had forgotten to click on one of the boxes)
and
said that it could not send the message. I therefore ended up writting it
several times. As it turned out, two of the times where it told me it had
not sent it, it had. I greatly apologise for all the inconvenience.

Secondly, yes, I mean to say the signal has a DC component. I would have
thought that impulsive noise, being cause by electron movement would
produce
an AC signal, otherwise where does the DC come from? The importance of the
time is because I would have thought that in the long term the antenna
would
resonate so as to produce a zero mean signal (AC). Sorry, the answer might
be common sense but I just fail to see it.

Thank you for your time and once again, sorry.


"Galilea" wrote in message
...
Hello, thank you for reading this post.

When analysing wideband impulse signals from a wideband antenna I have
realised that the average signal magnitude is not zero. I have thought
this
is because the reactance of the antenna at different frequencies varies
and
since it is a wideband antenna there can be energy measured since it is
only
for an extremely small period of time of 2-4 us. However, I am not sure
and
would greatly appreciate the views of this newsgroup.

I can understand all you are saying but in this case it is am impulsive
wideband signal (500 - 2.5 GHz), with a defined start and finish, caused by,
say things like car ignition systems and faulty thermostats. Surely a signal
like that would have all frequency components starting and ending at a
zero-crossing and then have full cycles, wouldn't it? Or maybe not because
of the multipath effects? Do you believe this can be the case in my
situation?

Thank you.



"Galilea" wrote in message
...
Hello, thank you for reading this post.

When analysing wideband impulse signals from a wideband antenna I have
realised that the average signal magnitude is not zero. I have thought
this
is because the reactance of the antenna at different frequencies varies
and
since it is a wideband antenna there can be energy measured since it is
only
for an extremely small period of time of 2-4 us. However, I am not sure
and
would greatly appreciate the views of this newsgroup.

Galilea wrote:
Secondly, yes, I mean to say the signal has a DC component. I would have
thought that impulsive noise, being cause by electron movement would produce
an AC signal, otherwise where does the DC come from?.

The DC is the result of your 2-4 uS sampling window. Make
your sampling window one second long and see what you get.

For instance, if you sample a 250 kHz signal for 2 uS and
if you happen to hit it at a zero-crossing going positive,
you will read the DC RMS value of the wave, having sampled
only 1/2 cycle.
--
73, Cecil http://www.qsl.net/w5dxp


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On Sat, 5 Feb 2005 16:55:35 GMT, "Galilea" wrote:

Hi Galilea,

You give the impression of being under the spell of a lot of
illusions. As you appear to be writing from an academic institution,
you should have been educated in the first principles of engineering:
a well described problem contains its own solution.

What you have been describing through your series of postings are
simple musings or rambling thoughts, nothing really coherent.
Stringing facts together does not really describe what you are
seeking. Let's examine this by parts:
I can understand all you are saying but in this case it is am impulsive
wideband signal (500 - 2.5 GHz), with a defined start and finish,
This is specific, detailed and uninformative. By definition, an
impulse has a defined start and finish, so nothing of value is added
by making such a declaration unless this start and finish are somehow
out of the ordinary. When you continue with:
caused by,
say things like car ignition systems and faulty thermostats.
"Like?" This is inspecific. Further, ignition systems and
thermostats have very little power in the spectrum you describe
(unless picoWatt levels are a disturbance to your true concern - if
so, this should be put on the table and all these abstractions swept
aside).
Surely a signal like that
Like what? This is becoming speculative without a basis.
would have all frequency components starting and ending at a
zero-crossing and then have full cycles, wouldn't it? Or maybe not because
of the multipath effects?
Here is every evidence of intellectual fishing because the answers to
your questions should be reasonably yes, but in actuality is no.
However, that yes/no aside, it is immaterial as this answer relates to
no larger over-riding question:
Do you believe this can be the case in my
situation?
No one knows your situation because you have no where described any
context to this string of statements, conflicting observations, and
speculations.

Basically you have offered a story with all middle and no beginning
and no end (somewhat mirroring much of the angst of your internal
conflict). Discard all these answers you are trying to force into
your problem and simply describe your problem.

First, how did you become aware you had a problem? Describe the first
thing that seemed unusual. Don't give us the theory of why -
subjectivity will always dominate the first impression and is fine as
an introduction.
Good Example: "I saw smoke."
Bad Example: "It was violating entropy."

Second, What else did you observe? Describe all other
characteristics, good and bad.
Good Example: "There were no flames, and it was unplugged."
Bad Example: "The Butterfly Effect would suggest that perhaps a nova
might be contributing to the imbalance of energy."

Third, Offer supporting details of measurement. Describe your
configuration, your tools, your method, and your results.
Good Example: "I examined my hair dryer; using a thermometer that I
placed at the exhaust; and found it read 300°C Over several minutes
it fell to 100°C and continued smoking."
Bad Example: "The thermal emission did not balance with the absence
of the standard power application of 900W."

Fourth, Describe those components that are directly involved in
conjunction with the observations and those that bear no relation, but
are supported by normal observations.
Good Example: "Cooling is evident from it not being plugged in,
however smoke is evidence of a continued process related to the
heater."
Bad Example: "Since there was no power in, there should have been no
power out. Isn't this a violation of the conservation of energy?"

Fifth, Localize the problem through refinement of measurements. Split
the problem in two and examine characteristics. If you obtain normal
data, split the problem in two again between this point and the source
of problematic data and repeat.
Good Example: "On close inspection I observed a long ash."
Bad Example: "I plugged it in and the imbalance of entropy became
dramatic."

Sixth, Describe the probable cause.
Good Example: "Hair had been drawn into the inlet and ignited by the
heater."
Bad Example: "There is every indication that a possible nova, through
the Butterfly Effect, created an imbalance in the continuum of energy
such that local effects produced a surplus bias of caloric emanation."

73's
Richard Clark, KB7QHC

Galilea wrote:
I can understand all you are saying but in this case it is am impulsive
wideband signal (500 - 2.5 GHz), with a defined start and finish, caused by,
say things like car ignition systems and faulty thermostats. Surely a signal
like that would have all frequency components starting and ending at a
zero-crossing and then have full cycles, wouldn't it? Or maybe not because
of the multipath effects? Do you believe this can be the case in my
situation?

Thank you.



"Galilea" wrote in message
...

Hello, thank you for reading this post.

When analysing wideband impulse signals from a wideband antenna I have
realised that the average signal magnitude is not zero. I have thought

this

is because the reactance of the antenna at different frequencies varies

and

since it is a wideband antenna there can be energy measured since it is

only

for an extremely small period of time of 2-4 us. However, I am not sure

and

would greatly appreciate the views of this newsgroup.






If the antenna is very wideband and isn't acting like a filter,
you can do a Fourier analysis on a series of pulses and decide for
yourself whether there is a DC component or not. Or, if there's only
one pulse, you can use the Fourier integral to find the amplitude
distribution across the frequency spectrum. I don't think you
should be too surprised to find a DC component in a series of
pulses, or even in a single pulse.
73,
Tom Donaly, KA6RUH

The average value of a signal is its DC value. To receive and reproduce
a signal with a non-zero DC component means that your antenna, as well
as your receiver, has to have response to DC. To generate such a signal
would require a static electric and/or magnetic field, which can't
propagate. So it's not possible for a signal you're receiving to have a
non-zero average value.

If it doesn't seem to be zero, there's something wrong with your
measurement system.

Roy Lewallen, W7EL

Thank you for all your help.

Richard, just because someone writes from an academic institution doesn't
mean they have had an academic education. This institution provides to
anyone who is willing to pay from the whole city and its surroundings with a
connection. I, for one, don't have one and it has just been recently, since
I started to work here that I have become interested from looking around and
talking to people during my shifts. Just because I am trying to learn by my
own means doesn't mean you have to rub my lack of knowledge in.

Once again, thank you all for your help.


"Galilea" wrote in message
...
Hello, thank you for reading this post.

When analysing wideband impulse signals from a wideband antenna I have
realised that the average signal magnitude is not zero. I have thought
this
is because the reactance of the antenna at different frequencies varies
and
since it is a wideband antenna there can be energy measured since it is
only
for an extremely small period of time of 2-4 us. However, I am not sure
and
would greatly appreciate the views of this newsgroup.

"Roy Lewallen" wrote
The average value of a signal is its DC value. To receive and reproduce a
signal with a non-zero DC component means that your antenna, as well as
your receiver, has to have response to DC. To generate such a signal would
require a static electric and/or magnetic field, which can't propagate. So
it's not possible for a signal you're receiving to have a non-zero average
value.
________________

Pure DC doesn't radiate, but there can be a DC component in the modulation
of an RF wave that does radiate. An example is analog broadcast television,
which has a highly asymmetric RF waveform. It can transmit a constant (DC)
video value of any amplitude between reference black at 75% modulation and
reference white at 12-1/2% modulation.

RF

"Roy Lewallen" wrote in message
...
The average value of a signal is its DC value. To receive and reproduce
a signal with a non-zero DC component means that your antenna, as well
as your receiver, has to have response to DC. To generate such a signal
would require a static electric and/or magnetic field, which can't
propagate. So it's not possible for a signal you're receiving to have a
non-zero average value.

sure it is. and while the 'static' field itself doesn't propagate the
leading edge of a step from 0 to some 'static' value can propagate and if
you measure as it passes you will see the received signal go from 0 to the
static value and then stay there.

On Sun, 6 Feb 2005 08:03:39 -0600, "Richard Fry"
wrote:

It can transmit a constant (DC) video value of any amplitude

Hi OM,

This is absurd. Video is a modulation being carried on RF, no one
broadcasts baseband on anything but copper.

The equally absurd notion offered here originally of DC offset being
RECEIVED is another fanciful illusion. Any such measurement was
clearly an error of measurement or understanding.

73's
Richard Clark, KB7QHC

On Sun, 6 Feb 2005 15:59:36 -0000, "Dave" wrote:

leading edge of a step from 0 to some 'static' value

Hi Dave,

....negates the usage of "static" - clearly.

A step pulse is not "static" and in fact contains an infinite range of
frequencies all of which are NOT DC. This is called the genii out of
the bottle and no one here can (but no doubt will try to) put it back.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message...
On Sun, 6 Feb 2005 08:03:39 -0600,
"Richard Fry" wrote:

It can transmit a constant (DC) video value of any amplitude

Hi OM,

This is absurd. Video is a modulation being carried on RF, no one
broadcasts baseband on anything but copper.
__________________

Before calling this reality absurd, consider that a television station
transmits a video signal in/on an RF channel. The demodulated video
waveform in the TV receiver will be identical to the baseband video signal
applied to the TV tx -- including its DC components (subject to any
distortions along the transmission path).

If it wasn't ~ identical, a TV set could never "fade to black" when the
original image did, and low-luminance colors such as blue, red, brown etc
would be impossible to reproduce with their original chromaticity.

RF (ex-RCA Field Engineer, and installer of
hundreds of TV color studio and film cameras)

"Richard Clark" wrote in message
On Sun, 6 Feb 2005 15:59:36 -0000, "Dave" wrote:

leading edge of a step from 0 to some 'static' value

...negates the usage of "static" - clearly.

A step pulse is not "static" and in fact contains an infinite range of
frequencies all of which are NOT DC. This is called the genii out of
the bottle and no one here can (but no doubt will try to) put it back.
______________

You mis-read. There is a DC component _required_ to convey the steady
voltage values preceding and following the step pulse transition. He's not
saying that the step pulse transition itself is comprised of "DC."

RF

On Sun, 6 Feb 2005 10:46:48 GMT, "Galilea" wrote:

Just because I am trying to learn by my
own means doesn't mean you have to rub my lack of knowledge in.

This is reverse elitist soap opera.

Since you are unresponsive to technical discussion, let's talk about
manners. Littering your posts with apologies does not excuse rude
behavior. This is rubbing your nose into your lack of knowledge in
newsgroup etiquette (and teaching you about flaming). Responding to
others (much as you've done to me here) through YOUR own postings
quite clearly marks you as being indifferent to the standards of
protocol and this arrives clearly through ignorance.

In any society, bohemian or in the dress circle of the opera, it
doesn't take much native intelligence to FIRST observe how people
conduct themselves and THEN participate after having noted the rules
of the game.

73's
Richard Clark, KB7QHC

On Sun, 6 Feb 2005 12:06:38 -0600, "Richard Fry"
wrote:

Before calling this reality absurd, consider that a television station
transmits a video signal in/on an RF channel. The demodulated video
waveform in the TV receiver will be identical to the baseband video signal
applied to the TV tx -- including its DC components (subject to any
distortions along the transmission path).

Hi OM,

OK, this is after the reality: what you offer is either absurd, or
non-nutritive didacticism.

Throw enough capacitance on the output of a detector and you will get
nothing but D.C. and never observe an average of zero. So What? The
forced presumption that you should is laughable. The original
question is so clouded with speculation that elbowing fantasy into a
response allows for any statement to qualify as an "authoritative
answer." Save this stuff for White House Social Security math -
mathbonics?

73's
Richard Clark, KB7QHC

On Sun, 6 Feb 2005 12:12:40 -0600, "Richard Fry"
wrote:
"Richard Clark" wrote in message
On Sun, 6 Feb 2005 15:59:36 -0000, "Dave" wrote:
leading edge of a step from 0 to some 'static' value
...negates the usage of "static" - clearly.
You mis-read.

Hi OM,

Your failure to reconcile the meaning of static with a non-static
description is as much as I need read. This class of discussion is
revealed in the hallmark re-definition of terms to suit poor
arguments.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sun, 6 Feb 2005 15:59:36 -0000, "Dave" wrote:

leading edge of a step from 0 to some 'static' value

Hi Dave,

...negates the usage of "static" - clearly.

A step pulse is not "static" and in fact contains an infinite range of
frequencies all of which are NOT DC. This is called the genii out of
the bottle and no one here can (but no doubt will try to) put it back.

73's
Richard Clark, KB7QHC

you will of course note that i quoted the term 'static' to denote that it
was indeed not static in the infinite sense of mathematics, but in the real
sense of it being a constant value over some measured time period.

the other obvious thing you are missing is that DC is a frequency... and it
does come out in the Fourier transform as a frequency of zero with some
finite magnitude for any waveform who's average value is not zero. it does
not even require that the waveform stay at some value forever, a short pulse
going from 0v to 1v and back to 0v will have a DC component in its spectrum
both mathematically and on any meter that can properly respond to it.

On Sun, 6 Feb 2005 19:35:55 -0000, "Dave" wrote:

you will of course note that i quoted the term 'static' to denote that it
was indeed not static in the infinite sense of mathematics, but in the real
sense of it being a constant value over some measured time period.

Hi Dave,

This is fine as an elaboration that grows beyond the horizon of the
question. But it really serves no purpose but to embroider a glaring
lack of facts.

the other obvious thing you are missing is that DC is a frequency... and it
does come out in the Fourier transform as a frequency of zero with some
finite magnitude for any waveform who's average value is not zero. it does
not even require that the waveform stay at some value forever, a short pulse
going from 0v to 1v and back to 0v will have a DC component in its spectrum
both mathematically and on any meter that can properly respond to it.

After having done a quite rigorous contract with HP deeply involved in
both the strict math and the mechanics of Fourier, I am well versed to
know how not all Fourier Transforms offer equal outcomes - especially
with, or without D.C. as a product.

Pure Fourier mandates a waveform constant throughout all time (from
its inception to its end) and is strictly one of those "thought
experiments" when it comes to transients - obviously. This has been,
and is the first issue that comes with its classic requirements
clashing with utility.

Practical Fourier mandates that you remove all D.C. components through
what is called "windowing" your data. You can choose not to and enjoy
all the artifacts of spurious behavior (like frequency folding,
frequency blurring, and false baselines) and translate those results
into blighted proofs too. With transients, practical Fourier
techniques mandate the presumption that they are periodic through all
time by literally forcing the data set (through extensive reworking)
to fit this requirement (which returns us to classic expectation).
Such reworking of original data demands that you make a choice: you
either discard amplitude accuracy for the sake of frequency accuracy,
or discard frequency accuracy for the sake of amplitude accuracy. The
irony of this choice is that you have already discard D.C. and its
appearance within the product of results is imbued with error. Need I
ask if you know how much error? Ignorance to what accuracy your
transforms bring reduce arguments to platitudes.

Simple, day to day, practical applications of Fourier discard these
issues as trivialities immediately and offer no pretense of "accuracy"
because you couldn't appreciate it anyway (unless the designer of an
IIR or FIR was so incompetent as to be that obvious).

However, this goes beyond the pale to justify a glaring presumption
"average signal magnitude not zero" with the trappings of Fourier.
For one, absolutely no one knows what is meant by "impulsive
wideband signal (500 - 2.5 GHz)." This is so extremely vague as to be
supportable by a multitude of waveforms that have wildly different
Fourier results. For instance, there is the classic impulse of
physics, lightning, which is notoriously low in frequency content over
the interval cited. Clearly such impulsions suffered are not from
nature. But this begs forcing the nomenclature to fit the problem.
There are other impulses like a gated sine wave (which obviously
renders a zero average), or a swept sine wave (same obvious average),
or a ramp wave, or a saw tooth wave, or a triangle wave, or chirp
wave. The list of impulsive wideband signals is exhausting, but
hardly accommodating to the same universal expectation.

If our correspondent, Galilea, cannot come to terms with responding to
technical issues when seeking help, the growth of forced speculation
creates its own illusory discussion that is best limited to idle
conversation overheard in a ticket line waiting for a movie box office
to open.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sun, 6 Feb 2005 12:12:40 -0600, "Richard Fry"
wrote:
"Richard Clark" wrote in message
On Sun, 6 Feb 2005 15:59:36 -0000, "Dave" wrote:
leading edge of a step from 0 to some 'static' value
...negates the usage of "static" - clearly.
You mis-read.

Hi OM,

Your failure to reconcile the meaning of static with a non-static
description is as much as I need read. This class of discussion is
revealed in the hallmark re-definition of terms to suit poor
arguments.

73's
Richard Clark, KB7QHC
________________

Your rhetoric is evasive and blustery -- no doubt so you won't have to admit
publicly to an incomplete understanding of what you are responding to.

RF

Richard,

Utter nonsense.

73,
Gene
W4SZ

Richard Clark wrote:
On Sun, 6 Feb 2005 19:35:55 -0000, "Dave" wrote:


you will of course note that i quoted the term 'static' to denote that it
was indeed not static in the infinite sense of mathematics, but in the real
sense of it being a constant value over some measured time period.


Hi Dave,

This is fine as an elaboration that grows beyond the horizon of the
question. But it really serves no purpose but to embroider a glaring
lack of facts.


the other obvious thing you are missing is that DC is a frequency... and it
does come out in the Fourier transform as a frequency of zero with some
finite magnitude for any waveform who's average value is not zero. it does
not even require that the waveform stay at some value forever, a short pulse
going from 0v to 1v and back to 0v will have a DC component in its spectrum
both mathematically and on any meter that can properly respond to it.


After having done a quite rigorous contract with HP deeply involved in
both the strict math and the mechanics of Fourier, I am well versed to
know how not all Fourier Transforms offer equal outcomes - especially
with, or without D.C. as a product.

Pure Fourier mandates a waveform constant throughout all time (from
its inception to its end) and is strictly one of those "thought
experiments" when it comes to transients - obviously. This has been,
and is the first issue that comes with its classic requirements
clashing with utility.

Practical Fourier mandates that you remove all D.C. components through
what is called "windowing" your data. You can choose not to and enjoy
all the artifacts of spurious behavior (like frequency folding,
frequency blurring, and false baselines) and translate those results
into blighted proofs too. With transients, practical Fourier
techniques mandate the presumption that they are periodic through all
time by literally forcing the data set (through extensive reworking)
to fit this requirement (which returns us to classic expectation).
Such reworking of original data demands that you make a choice: you
either discard amplitude accuracy for the sake of frequency accuracy,
or discard frequency accuracy for the sake of amplitude accuracy. The
irony of this choice is that you have already discard D.C. and its
appearance within the product of results is imbued with error. Need I
ask if you know how much error? Ignorance to what accuracy your
transforms bring reduce arguments to platitudes.

Simple, day to day, practical applications of Fourier discard these
issues as trivialities immediately and offer no pretense of "accuracy"
because you couldn't appreciate it anyway (unless the designer of an
IIR or FIR was so incompetent as to be that obvious).

However, this goes beyond the pale to justify a glaring presumption
"average signal magnitude not zero" with the trappings of Fourier.
For one, absolutely no one knows what is meant by "impulsive
wideband signal (500 - 2.5 GHz)." This is so extremely vague as to be
supportable by a multitude of waveforms that have wildly different
Fourier results. For instance, there is the classic impulse of
physics, lightning, which is notoriously low in frequency content over
the interval cited. Clearly such impulsions suffered are not from
nature. But this begs forcing the nomenclature to fit the problem.
There are other impulses like a gated sine wave (which obviously
renders a zero average), or a swept sine wave (same obvious average),
or a ramp wave, or a saw tooth wave, or a triangle wave, or chirp
wave. The list of impulsive wideband signals is exhausting, but
hardly accommodating to the same universal expectation.

If our correspondent, Galilea, cannot come to terms with responding to
technical issues when seeking help, the growth of forced speculation
creates its own illusory discussion that is best limited to idle
conversation overheard in a ticket line waiting for a movie box office
to open.

73's
Richard Clark, KB7QHC

Richard,

Utter nonsense.

73,
Gene
W4SZ

Richard Clark wrote:
On Sun, 6 Feb 2005 19:35:55 -0000, "Dave" wrote:


you will of course note that i quoted the term 'static' to denote that it
was indeed not static in the infinite sense of mathematics, but in the real
sense of it being a constant value over some measured time period.


Hi Dave,

This is fine as an elaboration that grows beyond the horizon of the
question. But it really serves no purpose but to embroider a glaring
lack of facts.


the other obvious thing you are missing is that DC is a frequency... and it
does come out in the Fourier transform as a frequency of zero with some
finite magnitude for any waveform who's average value is not zero. it does
not even require that the waveform stay at some value forever, a short pulse
going from 0v to 1v and back to 0v will have a DC component in its spectrum
both mathematically and on any meter that can properly respond to it.


After having done a quite rigorous contract with HP deeply involved in
both the strict math and the mechanics of Fourier, I am well versed to
know how not all Fourier Transforms offer equal outcomes - especially
with, or without D.C. as a product.

Pure Fourier mandates a waveform constant throughout all time (from
its inception to its end) and is strictly one of those "thought
experiments" when it comes to transients - obviously. This has been,
and is the first issue that comes with its classic requirements
clashing with utility.

Practical Fourier mandates that you remove all D.C. components through
what is called "windowing" your data. You can choose not to and enjoy
all the artifacts of spurious behavior (like frequency folding,
frequency blurring, and false baselines) and translate those results
into blighted proofs too. With transients, practical Fourier
techniques mandate the presumption that they are periodic through all
time by literally forcing the data set (through extensive reworking)
to fit this requirement (which returns us to classic expectation).
Such reworking of original data demands that you make a choice: you
either discard amplitude accuracy for the sake of frequency accuracy,
or discard frequency accuracy for the sake of amplitude accuracy. The
irony of this choice is that you have already discard D.C. and its
appearance within the product of results is imbued with error. Need I
ask if you know how much error? Ignorance to what accuracy your
transforms bring reduce arguments to platitudes.

Simple, day to day, practical applications of Fourier discard these
issues as trivialities immediately and offer no pretense of "accuracy"
because you couldn't appreciate it anyway (unless the designer of an
IIR or FIR was so incompetent as to be that obvious).

However, this goes beyond the pale to justify a glaring presumption
"average signal magnitude not zero" with the trappings of Fourier.
For one, absolutely no one knows what is meant by "impulsive
wideband signal (500 - 2.5 GHz)." This is so extremely vague as to be
supportable by a multitude of waveforms that have wildly different
Fourier results. For instance, there is the classic impulse of
physics, lightning, which is notoriously low in frequency content over
the interval cited. Clearly such impulsions suffered are not from
nature. But this begs forcing the nomenclature to fit the problem.
There are other impulses like a gated sine wave (which obviously
renders a zero average), or a swept sine wave (same obvious average),
or a ramp wave, or a saw tooth wave, or a triangle wave, or chirp
wave. The list of impulsive wideband signals is exhausting, but
hardly accommodating to the same universal expectation.

If our correspondent, Galilea, cannot come to terms with responding to
technical issues when seeking help, the growth of forced speculation
creates its own illusory discussion that is best limited to idle
conversation overheard in a ticket line waiting for a movie box office
to open.

73's
Richard Clark, KB7QHC

Richard,

Utter nonsense.

73,
Gene
W4SZ

Richard Clark wrote:
On Sun, 6 Feb 2005 19:35:55 -0000, "Dave" wrote:


you will of course note that i quoted the term 'static' to denote that it
was indeed not static in the infinite sense of mathematics, but in the real
sense of it being a constant value over some measured time period.


Hi Dave,

This is fine as an elaboration that grows beyond the horizon of the
question. But it really serves no purpose but to embroider a glaring
lack of facts.


the other obvious thing you are missing is that DC is a frequency... and it
does come out in the Fourier transform as a frequency of zero with some
finite magnitude for any waveform who's average value is not zero. it does
not even require that the waveform stay at some value forever, a short pulse
going from 0v to 1v and back to 0v will have a DC component in its spectrum
both mathematically and on any meter that can properly respond to it.


After having done a quite rigorous contract with HP deeply involved in
both the strict math and the mechanics of Fourier, I am well versed to
know how not all Fourier Transforms offer equal outcomes - especially
with, or without D.C. as a product.

Pure Fourier mandates a waveform constant throughout all time (from
its inception to its end) and is strictly one of those "thought
experiments" when it comes to transients - obviously. This has been,
and is the first issue that comes with its classic requirements
clashing with utility.

Practical Fourier mandates that you remove all D.C. components through
what is called "windowing" your data. You can choose not to and enjoy
all the artifacts of spurious behavior (like frequency folding,
frequency blurring, and false baselines) and translate those results
into blighted proofs too. With transients, practical Fourier
techniques mandate the presumption that they are periodic through all
time by literally forcing the data set (through extensive reworking)
to fit this requirement (which returns us to classic expectation).
Such reworking of original data demands that you make a choice: you
either discard amplitude accuracy for the sake of frequency accuracy,
or discard frequency accuracy for the sake of amplitude accuracy. The
irony of this choice is that you have already discard D.C. and its
appearance within the product of results is imbued with error. Need I
ask if you know how much error? Ignorance to what accuracy your
transforms bring reduce arguments to platitudes.

Simple, day to day, practical applications of Fourier discard these
issues as trivialities immediately and offer no pretense of "accuracy"
because you couldn't appreciate it anyway (unless the designer of an
IIR or FIR was so incompetent as to be that obvious).

However, this goes beyond the pale to justify a glaring presumption
"average signal magnitude not zero" with the trappings of Fourier.
For one, absolutely no one knows what is meant by "impulsive
wideband signal (500 - 2.5 GHz)." This is so extremely vague as to be
supportable by a multitude of waveforms that have wildly different
Fourier results. For instance, there is the classic impulse of
physics, lightning, which is notoriously low in frequency content over
the interval cited. Clearly such impulsions suffered are not from
nature. But this begs forcing the nomenclature to fit the problem.
There are other impulses like a gated sine wave (which obviously
renders a zero average), or a swept sine wave (same obvious average),
or a ramp wave, or a saw tooth wave, or a triangle wave, or chirp
wave. The list of impulsive wideband signals is exhausting, but
hardly accommodating to the same universal expectation.

If our correspondent, Galilea, cannot come to terms with responding to
technical issues when seeking help, the growth of forced speculation
creates its own illusory discussion that is best limited to idle
conversation overheard in a ticket line waiting for a movie box office
to open.

73's
Richard Clark, KB7QHC

On Sun, 06 Feb 2005 21:58:05 GMT, Gene Fuller
wrote:

Utter nonsense.

Hi Gene,

You had to post that three times?

Oh well, seems the season for deeply insightful criticism that appears
to be following the value of the dollar in the world market. Was that
your 1½¢ worth?

Barring any discussion of conflicting experience, I would say it was
worth every penny. You can put it into a privatized SS account and
recoup massive earnings - if the dollar would just tread water. Don't
invest in cotton or rice futures though.... [Feb. 5 - President Bush
will seek deep cuts in farm and commodity programs in his new budget]

73's
Richard Clark, KB7QHC

obviously this discussion has ended... we are down to the 'just poo poo'
what you don't understand level... next comes name calling and personal
attacks, so its time to leave.

"Gene Fuller" wrote in message
...
Richard,

Utter nonsense.

73,
Gene
W4SZ

Richard Clark wrote:
On Sun, 6 Feb 2005 19:35:55 -0000, "Dave" wrote:


you will of course note that i quoted the term 'static' to denote that
it
was indeed not static in the infinite sense of mathematics, but in the
real
sense of it being a constant value over some measured time period.


Hi Dave,

This is fine as an elaboration that grows beyond the horizon of the
question. But it really serves no purpose but to embroider a glaring
lack of facts.


the other obvious thing you are missing is that DC is a frequency... and
it
does come out in the Fourier transform as a frequency of zero with some
finite magnitude for any waveform who's average value is not zero. it
does
not even require that the waveform stay at some value forever, a short
pulse
going from 0v to 1v and back to 0v will have a DC component in its
spectrum
both mathematically and on any meter that can properly respond to it.


After having done a quite rigorous contract with HP deeply involved in
both the strict math and the mechanics of Fourier, I am well versed to
know how not all Fourier Transforms offer equal outcomes - especially
with, or without D.C. as a product.

Pure Fourier mandates a waveform constant throughout all time (from
its inception to its end) and is strictly one of those "thought
experiments" when it comes to transients - obviously. This has been,
and is the first issue that comes with its classic requirements
clashing with utility.

Practical Fourier mandates that you remove all D.C. components through
what is called "windowing" your data. You can choose not to and enjoy
all the artifacts of spurious behavior (like frequency folding,
frequency blurring, and false baselines) and translate those results
into blighted proofs too. With transients, practical Fourier
techniques mandate the presumption that they are periodic through all
time by literally forcing the data set (through extensive reworking)
to fit this requirement (which returns us to classic expectation).
Such reworking of original data demands that you make a choice: you
either discard amplitude accuracy for the sake of frequency accuracy,
or discard frequency accuracy for the sake of amplitude accuracy. The
irony of this choice is that you have already discard D.C. and its
appearance within the product of results is imbued with error. Need I
ask if you know how much error? Ignorance to what accuracy your
transforms bring reduce arguments to platitudes.

Simple, day to day, practical applications of Fourier discard these
issues as trivialities immediately and offer no pretense of "accuracy"
because you couldn't appreciate it anyway (unless the designer of an
IIR or FIR was so incompetent as to be that obvious).

However, this goes beyond the pale to justify a glaring presumption
"average signal magnitude not zero" with the trappings of Fourier.
For one, absolutely no one knows what is meant by "impulsive
wideband signal (500 - 2.5 GHz)." This is so extremely vague as to be
supportable by a multitude of waveforms that have wildly different
Fourier results. For instance, there is the classic impulse of
physics, lightning, which is notoriously low in frequency content over
the interval cited. Clearly such impulsions suffered are not from
nature. But this begs forcing the nomenclature to fit the problem.
There are other impulses like a gated sine wave (which obviously
renders a zero average), or a swept sine wave (same obvious average),
or a ramp wave, or a saw tooth wave, or a triangle wave, or chirp
wave. The list of impulsive wideband signals is exhausting, but
hardly accommodating to the same universal expectation.

If our correspondent, Galilea, cannot come to terms with responding to
technical issues when seeking help, the growth of forced speculation
creates its own illusory discussion that is best limited to idle
conversation overheard in a ticket line waiting for a movie box office
to open.

73's
Richard Clark, KB7QHC

Gene Fuller wrote:

Richard,

Utter nonsense.

I don't think so, Gene. I have to read Richards posts twice on
occasion, but this is pretty spot on.

- Mike KB3EIA -
Richard Clark wrote:

On Sun, 6 Feb 2005 19:35:55 -0000, "Dave" wrote:


you will of course note that i quoted the term 'static' to denote
that it
was indeed not static in the infinite sense of mathematics, but in
the real
sense of it being a constant value over some measured time period.



Hi Dave,

This is fine as an elaboration that grows beyond the horizon of the
question. But it really serves no purpose but to embroider a glaring
lack of facts.

rest snipped

Surely as a former broadcast engineer you're acquainted with a circuit
called a "DC restorer". This is a circuit which is always present in a
TV receiver. In its simplest form, it's just a diode clamping circuit,
although I've made very good ones with an FET switch and hold capacitor.
What it does is to set the sync pulse tip to a fixed DC value, which
then causes the rest of the TV waveform to be at a fixed DC value. This
is how the DC information is "transmitted". The actual TV waveform is AC
coupled, as it must be, and its DC values are established in the
receiver by the DC restorer.

No DC value is transmitted.

You should be able to find an explanation of this in any basic text on
the principles of television transmission and reception.

Roy Lewallen, W7EL

Richard Fry wrote:
______________

You mis-read. There is a DC component _required_ to convey the steady
voltage values preceding and following the step pulse transition. He's
not saying that the step pulse transition itself is comprised of "DC."

RF

Richard Fry wrote:

Before calling this reality absurd, consider that a television station
transmits a video signal in/on an RF channel. The demodulated video
waveform in the TV receiver will be identical to the baseband video
signal applied to the TV tx -- including its DC components (subject to
any distortions along the transmission path).

If it wasn't ~ identical, a TV set could never "fade to black" when the
original image did, and low-luminance colors such as blue, red, brown
etc would be impossible to reproduce with their original chromaticity.

RF (ex-RCA Field Engineer, and installer of
hundreds of TV color studio and film cameras)

You perhaps never installed a receiver. Without its DC restorer circuit,
the problems you mention do indeed exist. In a black-and-white set, a
large white area will cause everything else to go black, to maintain a
zero average. But the DC information is transmitted as a level
difference between the sync tip and the "porches". At the receiver (as I
mentioned in another post), this voltage *difference* is turned into a
DC value. No DC is transmitted.

Surely a little bit of thought will establish why direct transmission of
DC isn't possible beyond the range of a static field.

Roy Lewallen, W7EL

"Roy Lewallen" wrote
Surely as a former broadcast engineer you're acquainted with a circuit
called a "DC restorer". This is a circuit which is always present in a TV
receiver. In its simplest form, it's just a diode clamping circuit,
although I've made very good ones with an FET switch and hold capacitor.
What it does is to set the sync pulse tip to a fixed DC value, which then
causes the rest of the TV waveform to be at a fixed DC value. This is how
the DC information is "transmitted". The actual TV waveform is AC coupled,
as it must be, and its DC values are established in the receiver by the DC
restorer....
_________________________

I must respectfully disagree with that, Sir. The baseband video signal is *
DC coupled * through analog TV transmitters . The peak power of a
transmitted TV RF waveform is a fixed value, at the power corresponding to
the licensed ERP of the station, occurring at the peak of sync pulses, and
independent of program video. Transmitted _average_ power is a function of
the video envelope.

Video is transmitted with negative polarity; 75% modulation when video is
black, and 12-1/2% modulation when it is white. The video waveform AS
TRANSMITTED can contain a steady state (DC) value throughout the video field
for any amplitude at or between those values (actually the color subcarrier
can exceed these for some conditions).

The circuits in a TV receiver cannot pass the DC component, thus the need
for a DC restorer following the video demodulator. But the point remains
that the transmitted TV waveform can, and often does contain a DC component,
and that this DC component is required for accurate reproduction of the
original video on the TV display.

RF

PS: I still AM a broadcast engineer.

"Roy Lewallen" wrote

But the DC information is transmitted as a level difference
between the sync tip and the "porches". At the receiver (as I mentioned in
another post), this voltage *difference* is turned into a DC value. No DC
is transmitted.
_________________

As I wrote in my slightly earlier post to you on this, the actual video
waveform is DC coupled through an analog TV transmitter. Please refer to
that post for more on this topic.

RF

"Roy Lewallen" wrote about broadcast television waveforms:
... No DC value is transmitted....
and
...The actual TV waveform is AC coupled, as it must be, and its
DC values are established in the receiver by the DC restorer...
___________________________

Please think about this. Standard TV color bars are produced by mixing the
outputs of three video pulse generators. The pulses are square waves, with
amplitude limits of 0 and 0.7VDC (~0.25µs transitions). These three video
waveforms are shown in Figure 7-1 in the paper hyperlinked at the bottom of
this post.

The DC present during the "on" time of these video pulses is
indistinguishable from the DC supplied by a continuous 0.7VDC source, over
the same, steady-state time interval. The DC and near-DC values of this
video must be available to the TV display device in order to accurately show
the color bar signal (and any other video waveform).

Low frequency content is lost when video is AC-coupled through a TV
transmitter (or any other circuit). A TV set DC restorer sets and
maintains the DC axis on which the pulse rides, but that does not correct
the distortion of the pulse waveform resulting from loss of its low
frequency content near zero hertz (DC).

Also recall that even the shortest pulse* that can pass undistorted through
the ~4MHz video bandwidth of the US broadcast TV standard contains most of
its energy at, and near zero hertz, e.g., DC.

*a sin² pulse with 0.25µs transitions

So DC _is_ , and must be conveyed by analog broadcast (and other) television
systems, because television wouldn't work well otherwise. It isn't DC as
you may think of it coming out of a battery, but it is DC, nevertheless, and
identical to battery DC of the same amplitude, when compared over equal,
steady-state intervals.

http://www.tek.com/Measurement/cgi-b...Set=television

RF

Richard Clark wrote:

"Dave" wrote:
you will of course note that i quoted the term 'static' to denote that it
was indeed not static in the infinite sense of mathematics, but in the real
sense of it being a constant value over some measured time period.

This is fine as an elaboration that grows beyond the horizon of the
question. But it really serves no purpose but to embroider a glaring
lack of facts.

Perhaps the measured DC value is not the result of EM waves
but the result of mechanical depositing of charge on the
antenna. I assume that wind/snow static is DC - enough DC
to cause arcing across a coax connector.
--
73, Cecil http://www.qsl.net/w5dxp


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Richard,

Sorry about the triple. I was so caught up in the excitement (constant
throughout all time) of your message I just couldn't stop.

Quote:

"After having done a quite rigorous contract with HP deeply involved in
both the strict math and the mechanics of Fourier, I am well versed to
know how not all Fourier Transforms offer equal outcomes - especially
with, or without D.C. as a product.

Pure Fourier mandates a waveform constant throughout all time (from
its inception to its end)"


I can ignore the name-dropping, but I cannot ignore the incorrect
statement about "Pure Fourier". There is no mandate of constancy even
for the purest Fourier transform. The function needs only to be
moderately well-behaved, including single valued and integrable.

Perhaps you are confusing Fourier series analysis with Fourier transform
analysis?

(By the way, for any of the lurkers out there, I did not say a word
about "DC". That is a trivial matter subject only to one's choice of
wording. There is no apparent disagreement on the reality, only the
description.)


73,
Gene
W4SZ


Richard Clark wrote:
On Sun, 06 Feb 2005 21:58:05 GMT, Gene Fuller
wrote:


Utter nonsense.


Hi Gene,

You had to post that three times?

Oh well, seems the season for deeply insightful criticism that appears
to be following the value of the dollar in the world market. Was that
your 1½¢ worth?

Barring any discussion of conflicting experience, I would say it was
worth every penny. You can put it into a privatized SS account and
recoup massive earnings - if the dollar would just tread water. Don't
invest in cotton or rice futures though.... [Feb. 5 - President Bush
will seek deep cuts in farm and commodity programs in his new budget]

73's
Richard Clark, KB7QHC

On Mon, 07 Feb 2005 14:34:38 GMT, Gene Fuller
wrote:

I can ignore the name-dropping, but I cannot ignore the incorrect
statement about "Pure Fourier". There is no mandate of constancy even
for the purest Fourier transform. The function needs only to be
moderately well-behaved, including single valued and integrable.

Hi Gene,

In this case you are seriously wrong. There are no IFs ANDs or BUTs.
The loop hole of well-behaved is not enough with it being far too
inspecific.

The ONLY case where the Fourier Series resolves a correct
transformation is if you limit your data set (or for an Integration,
you define your limits) over an interval of n · 2 · PI for a periodic
function where n is an integer from 1..m. Further, you are resolution
limited if you fail to observe Nyquist's laws and under sample, or
fail to frequency limit your real data. This also segues into
Shannon's laws where you can observe the S+N/N in the transform
(discussed below). These concerns are EXTERNAL to the simple act of
transforming data, but are necessary correlatives that MUST be taken
into account.

If you fail even in this simple regard for periodicity (say looking at
only 359 degrees of the periodic function), the result is quite
dramatically different in the Fourier output. Even the casual
observer can immediately see the difference between the correct and
incorrect results, there is nothing ambiguous about it at all.

Perhaps you are confusing Fourier series analysis with Fourier transform
analysis?

No, I have done both, and I will drop the name again, at HP with their
work on Fourier Analysis equipment where I tested their FFT algorithms
(call them what you may, the basic underlying requirements do not
change). I was working with 24 Mathematicians AND Engineers - there
was nothing sloppy about the quality of up-front preparation. This
was a project 5 years in the making. They even wrote their own Pascal
compiler for 1000000 lines of code. I have also done IIRs and FIRs,
Wavelets, and a host of other frequency/time series decimation
analysis.

ALL Fourier techniques have requirements that go beyond the Fourier
math. These requirements (if you have any interest in accuracy)
cannot be ignored. If you have no interest in accuracy, you still
have to perform some of them, which is to say there are trade offs as
I mentioned previously. Ignoring them all simply reduces real data
into transformed garbage.

I have written FFT software that has resolved pure sine waves into a
transformation to a single bin with a statistical noise floor and ALL
spurious response down 200dB. To give an example of what 1° of
decimation error will do, it will inject 120dB of noise into the
product and spurs that are barely 10 to 20 dB down from the principle
bin (which also exhibits about 3dB error).

Much of what is available through college texts and on the web are
seriously under powered in their scope. College is not very
interested in scope, simply introduction. That is, unless you find
yourself in a undergrad (more probably grad school with the additional
considerations taken into account) engineering course dedicated to
modern implementations (practical Fourier) now largely focused on DSP
(which had its genesis in the IIR and FIR earlier implementations).

73's
Richard Clark, KB7QHC

Cecil Moore wrote:

Tam/WB2TT wrote:

"Galilea" wrote

When analysing wideband impulse signals from a wideband antenna I have
realised that the average signal magnitude is not zero. I have
thought this
is because the reactance of the antenna at different frequencies
varies and
since it is a wideband antenna there can be energy measured since it
is only
for an extremely small period of time of 2-4 us. However, I am not
sure and
would greatly appreciate the views of this newsgroup.

Are you saying the DC value is not 0 ?


He seems to be saying the DC value is not 0 for a sampling
time period of 2-4 uS which would of course be true for a
sine wave if, e.g., an odd number of positive cycles were
sampled along with an even number of negative cycles. Or
if the frequency was lower than 250 kHz. Plus all the
signals and noise are superposed.

Chances are fair that something is doing some rectifying somewhere.

ac6xg

Jim Kelley wrote:
Chances are fair that something is doing some rectifying somewhere.

It later occurred to me that wind/snow noise is
carried by static DC charged particles.
--
73, Cecil http://www.qsl.net/w5dxp


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