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Re: ao40 today





-------------Message réacheminé-----------------

Exp.:	"Richard D. Burgan", INTERNET:wc8j@raex.com
A:	[inconnu], INTERNET:amsat-bb@AMSAT.Org
	MCGWIER ROBERT, INTERNET:rwmcgwier@home.com
	
Date:	06/01/01 01:51 

RE:	Re: [amsat-bb] ao40 today

 
Bob,

On the www.amsat-dl.org/journal/adlj-p3d.htm page is a waterfall display (turned
horizontal) showing the AO-40 signal.  You can see the signal strength fast
fades in the blue background especially near the edges.  You can see the slower
fades in the signal line definition.  And you can see the 14 second telemetry
pattern.  The doppler "wobulation" shows clearly.

I don't know if you have seen this page yet.

I will try to capture an audio file for you.  My best shot will be Sunday
morning.  Then I'll be out of town (Houston, TX) for the week.

In what form would you prefer the audio?

73's de Rich @ WC8J

----

MCGWIER ROBERT wrote:

> 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
> >
> >
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >
>
> ----
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