Envelope-to: dave@picks.force9.co.uk
Delivery-date: Wed, 01 Feb 2006 16:04:41 +0000
From: Warren K2ORS/WD2XGJ <k2ors@comcast.net>
To: rsgb_lf_group@blacksheep.org,  rsgb_lf_group@blacksheep.org
Cc: "Andy" <actalbot@southsurf.com>
Date: Wed, 01 Feb 2006 16:03:54 +0000
Message-Id: <020120061603.5047.43E0DBEA0008965D000013B722064244130B97010D0A020E06979D0E03@comcast.net>
Subject: Re: LF: Can't see the wood for the trees
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Andy,

     Keep in mind that if you have tabular data then Microsoft Excel (as well as other programs) can do a fourier analysis.


--
73 Warren K2ORS/WD2XGJ
FN42hi
http://www.w4dex.com/wd2xgj.htm

 -------------- Original message ----------------------
From: "Andy" <actalbot@southsurf.com>
> Yes - that's the obvious bit I was missing - go back to first principles and
> do the actual Fourier transform on the waveform.
> 
> There ought to be a short cut, though, knowing the integral is finite and
> contains total power in the signal.   I had assumed the Dirichlet integral
> converged, but didn't know the result, so maybe that is the way to go.
> 
> Tnx
> Andy  G4JNT
> www.scrbg.org/g4jnt/
> 
> 
> 
> 
> 
> -----Original Message-----
> From: Warren K2ORS/WD2XGJ <k2ors@comcast.net>
> To: rsgb_lf_group@blacksheep.org <rsgb_lf_group@blacksheep.org>;
> rsgb_lf_group@blacksheep.org <rsgb_lf_group@blacksheep.org>
> Cc: Andy <actalbot@southsurf.com>
> Date: 2006/02/01 15:34
> Subject: Re: LF: Can't see the wood for the trees
> 
> 
> >Andy,
> >
> >      Unless I'm missing the meaning of your question, I believe you want
> the fourier coefficients to determine the amplitudes of the components
> making up the pulse train. Also, should you feel the need to integrate
> sin(x)/x, the so-called Dirichlet integral, it does converge and the
> definite integral from 0 to infinity of sin(x)/x = pi/2.  For reference see:
> >http://www.pupress.princeton.edu/books/maor/chapter_10.pdf
> >
> > I'm in the middle of a project at the moment but let me know if I'm on the
> right track - I could help with the fourier coefficients perhaps this
> evening.
> >
> >--
> >73 Warren K2ORS/WD2XGJ
> >FN42hi
> >http://www.w4dex.com/wd2xgj.htm
> >
> > -------------- Original message ----------------------
> >From: "Andy" <actalbot@southsurf.com>
> >> Can someone help with what should be obvious.
> >>
> >> I have a train of constant width pulses at a fixed repetition rate.   In
> the
> >> frequency domain these appear as a spectral comb with spacing at the
> >> repetition rate, whose amplitude  follows a SIN(X) / X shape depending on
> >> the pulse width, ie. the first null occuring at at 1/width and so on.
> >>
> >> What I'm getting tied up in knots trying to calculate is :
> >>
> >> What is the absolute amplitude (power) of just one individual tooth of
> the
> >> comb at any particular spacing.
> >>
> >> Assume the pulse waveform has, say,  1mW or 0dBm mean amplitude, and
> >> consists of 500us pulses at 40Hz PRI.   The duty cycle is 0.02, so the
> >> individual pulse power would have to be 50mW or 17dBm to get this mean.
> >> But what is the amplitude of the component at, say, 1kHz, or 1040Hz, or
> >> 10kHz ??
> >>
> >> It must be obvious, but I keep feeling the urge to integrate SIN(X) / X
> >> which is not funny and way beyond my maths capabilities!!
> >>
> >> The figures given above are those for the 5MHz beacon sounder sequence.
> >> The amplitude trace on the monitoring software during the sounder
> sequence
> >> is measuring just one line of the comb ( F = 0,  the carrier) , and
> appears
> >> to suggest this is about 30 - 35dB down on the CW part.  That is -17dB
> from
> >> the peak/mean  as above, but where does the other 13 - 18dB come from?
> >>
> >> Tearing hair out
> >>
> >> Andy  G4JNT
> >> www.scrbg.org/g4jnt/
> >>
> >>
> >>
> >
> >
> >
> 
>