[amsat-bb] Re: Theoretical Question

lucleblanc6 at videotron.ca lucleblanc6 at videotron.ca
Sun Oct 13 18:55:25 PDT 2013

On 13 Oct 2013 at 18:30, Dave Marthouse wrote:

> This isn't a question regarding amateur satellites but it is an interesting
> theoretical one to pose here and the same laws of physics apply.  I know
> that the higher the frequency that is transmitted from a satellite the
> larger the Doppler shift will be.  The Iridium satellites transmit at around
> 1.5gHZ.  At that frequency I know the Doppler is large.  How do they manage
> to keep the portable handsets on the ground locked to the signal?  Are the
> handsets frequency agile to an extent?  How do they achieve frequency lock
> so that the digital signals are decoded?
> Dave Marthouse N2AAM
> dmarthouse at gmail.com
Interesting question Dave

I suspect as the XM/SIRIUS radio a data signal is sent back to the receiver position to minimized the doppler effect and some sort of data 
error correction also help to counteract the doppler effect. A similar system is implemented into the wxtoimg NOAA weather satellite fax 
decoding software.

It is an educated guess who only need to be reeducated... Lets say my Sirius receiver in a plain flat field suffer some signal breaks that 
i can't explain.

Luc Leblanc VE2DWE

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