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Re: ao40 today



I hadn't thought about the specular reflections off the
engine.  That was an oversight.    Talk about
dynamic multipath!

Bob

----- Original Message ----- 
From: "Phil Karn" <karn@ka9q.net>
To: <rwmcgwier@home.com>
Cc: <amsat-bb@amsat.org>
Sent: Sunday, January 07, 2001 6:07 PM
Subject: Re: [amsat-bb] ao40 today


> ><<The nice thing about this "wobbulation" is:
> >IT'S A COMPLETELY PREDICTABLE PROCESS. >>
> 
> After thinking about it some more, I'm not sure this is true. At high
> squint angles, the other spacecraft components around the antenna
> could unpredictably affect the pattern as the spacecraft spins.
> 
> Consider the possibility of a specular "glint" off the engine bell,
> e.g., as the S-band antenna rotates in front of it.  Along with the
> jump in amplitude there would also be a sudden jump in carrier phase
> due to the extra distance the signal would have to travel from the
> S-band antenna to the engine bell and back, a distance of perhaps a
> meter. That's quite a few wavelengths at 13 cm.
> 
> The presence of modulation makes it hard to see just the spin-induced
> doppler in a FFT waterfall. It should be pretty easy in my DSP demod
> to strip the modulation from the signal, leaving an unmodulated
> carrier plus noise.  I'll give that a try.
> 
> Phil
> 
> 

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