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Re: ao40 today



Ed Krome loaned me the only S band equipment
I ever owned back in the DOVE commanding
days so I can't hear the signal ;-(.

I am trying to get a picture of the depth of the
fades, and the signal strength, etc. with various
classes of stations.   Phil is working on a new
demodulator for this signal, but from my conversations
with him, I think his assumptions are that the
wobbulation modulation is smaller than this.

<<The nice thing about this "wobbulation" is:
IT'S A COMPLETELY PREDICTABLE PROCESS. >>

This means that we can, inside the modem,
completely determine the parameters for this
spin modulation and then PREDICT the frequency
and phase of the carrier based on our signal
determined parameters and greatly improve the
performance of the demodulator.  If we are going
to be stuck on this setting for a while (and I
believe we are going to be for quite a while),
then I would like write a piece of code that
does this modeling.  I will write it in C.  I will post
it for everyone to use.  I will then attempt to
put it into the DSP2232 demod.    It is my belief
that hard limiting versions of the demods and
others done with very narrow noise bandwidth
second order loops made serious assumptions
about narrowness of the tracking loop that will
prevent it from tracking this signal and that it is
not possible to easily modify them to handle this.

What do I need?  I need some captured signal
in a wav file in order to do this work.   I need for
it to be a really good signal in terms of its overall
amplitude.  I would prefer some near the minimum
of this wobbulation and some near when it is
getting bad enough to cause all of the demods to
fail.

Bob


----- Original Message -----
From: "Bill Magnusson" <williamb@netc.net.au>
To: "AMSAT BB" <amsat-bb@AMSAT.Org>
Sent: Thursday, January 04, 2001 11:29 PM
Subject: Re: [amsat-bb] ao40 today


> Hi Phil ..... list
> >
>
> >I think the +/1 200 Hz drift might be due to the rotation of the
> spacecraft.
> >
> >Let's compute what it should be.
> <snip>
> >
>  >= +/-14.2 Hz.
> >
> <snip>
>
> My observations agree with this. The wobulation shows up clearly on a
> waterfall display. At squints of around 45 degrees the waterfall display
> shows 'squiggles' of around +/- 1mm on my screen. On the w/f display 150mm
> represents approx. 1500Hz ... ie. approx. 10Hz per mm on my screen so the
> 'squiggles' represent (very approx. but in the ball-park), +/- 10Hz on
each
> rotation of the spacecraft. Considering that the figure would increase
with
> squints out to 90 degrees, Phil's calculations of the theoretical Doppler
> look to me to pretty much account for the 'wobulation'.
>
> Bill Magnusson ... vk3jt
> Milawa Australia
>
>
> ----
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>

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