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