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From: FatScouser on 3 Jun 2010 04:26
>On 6/2/2010 12:46 PM, FatScouser wrote:
>> Hi,
>>
>> Could someone recommend the best spectrum analysis software package -
or
>> method - for dealing with signals having only partial waves?
>
> ...
>
>What is a partial wave?
>
>Jerry
>--
>Engineering is the art of making what you want from things you can get.
>�����������������������������������������������������������������������
>

Hi Jerry,

Yeah - am maybe being contradictory there... To give an example:

If you use SigView (with its default settings, i.e. no windows, zero
padding, or averaging) to analyse a periodic sine with 4 wavelengths, say,
you get a nice spike in the spectrum at expected frequency.

But if you feed in a 'partial' sine wave, i.e. non-periodic 1 wavelength or
less, said spike doesn't show.

I guess attempting to fourier transform - which assumes periodicity - is
like trying to push a square peg through a round hole, so I shouldn't be
surprised. I just don't know at this stage the correct method to use.

Cheers, John
From: FatScouser on 3 Jun 2010 04:35
>On 6/2/2010 2:20 PM, Jerry Avins wrote:
>> On 6/2/2010 12:46 PM, FatScouser wrote:
>>> Hi,
>>>
>>> Could someone recommend the best spectrum analysis software package -
or
>>> method - for dealing with signals having only partial waves?
>>
>> ...
>>
>> What is a partial wave?
>>
>> Jerry
>
>This is my first thought:
>
>http://www.youtube.com/watch?v=-TpW8xa0A-w
>
>then maybe this:
>
>http://www.youtube.com/watch?v=o2ZICNCxR8w
>
>past that I'm not sure.
>
>--
>Eric Jacobsen
>Minister of Algorithms
>Abineau Communications
>http://www.abineau.com
>

Very droll .. ;o)))
From: illywhacker on 3 Jun 2010 06:08
On Jun 3, 10:26 am, "FatScouser"
<john.hague(a)n_o_s_p_a_m.truebit.co.uk> wrote:
> If you use SigView (with its default settings, i.e. no windows, zero
> padding, or averaging) to analyse a periodic sine with 4 wavelengths, say,
> you get a nice spike in the spectrum at expected frequency.
>
> But if you feed in a 'partial' sine wave, i.e. non-periodic 1 wavelength or
> less, said spike doesn't show.
>
> I guess attempting to fourier transform - which assumes periodicity - is
> like trying to push a square peg through a round hole, so I shouldn't be
> surprised. I just don't know at this stage the correct method to use.

The method depends on the goal.

'Frequency content' is *defined* by the Fourier transform. If you send
in one wavelength of a sine wave in signal of total length more than
one wavelength, then the frequency content is not just that of the
sine wave from which you 'cut' the wavelength. The 'cutting' process
itself introduces an infinite number of other frequencies.

Equally, if you feed in less than one wavelenght of a sine wave, then
you implicitly have a jump at the boundary due to lack of periodicity,
and again you are introducing an infinite number of other frequencies.

If you wish to define 'frequency content' differently, you can do so,
and then analyse your signals appropriately. But this definition is up
to you, and doubtless depends on your ultimate goal, i.e. the
application, which you have not described. It may be connected to
prior information about some 'total' signal of which you possess
knowledge of only a part, or it may simply be a definition of your
choice.

illywhacker;
From: Mikolaj on 3 Jun 2010 06:25
Dnia 03-06-2010 o 10:26:51 FatScouser
<john.hague(a)n_o_s_p_a_m.truebit.co.uk> napisał(a):

(...)
> I guess attempting to fourier transform - which assumes periodicity
(...)

There is no such assumption.
This transform is decomposition within periodic signals.
Maybe other transforms would fit to what you expect.

> I just don't know at this stage the correct method to use.

Are you looking for periodic component in energy signal
(finite time and amplitude - relatively short and strange shaped impulse
:))?
Hmm, why?
Their's spectrum is infinite which means energy is smashed to all
frequencies
because of discontinuity in time.
So you will find no spikes
but smooth fields.

The ultimate question is
do you know what are you looking for?


--
Mikolaj
From: Clay on 3 Jun 2010 09:40
On Jun 2, 5:20 pm, Jerry Avins <j...(a)ieee.org> wrote:
> On 6/2/2010 12:46 PM, FatScouser wrote:
>
> > Hi,
>
> > Could someone recommend the best spectrum analysis software package - or
> > method - for dealing with signals having only partial waves?
>
>    ...
>
> What is a partial wave?
>
> Jerry
> --
> Engineering is the art of making what you want from things you can get.

My 1st thought is "partial wave expansion" in physics. This has to do
with the scattering of a plane wave by a particle where the resulting
scattered wave is expressed as a sum of spherical waves each with its
own amplitude and phase shift. But I'm quite sure the OP didn't want
this version. LOL.

Clay

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