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RE: Doppler #2



Emily, I completely disagree with your assessment. The modulation frequency would have to change at the same rate as the carrier but it is unnoticeable because of the small percentage of change. If a signal at 150Mhz is doppler shifted - 10Khz this will cause a tone of 3Khz modulation to shift down 0.2 Hz if my math is correct. You would never notice this.

As an example if the sat is moving away from you at half the speed of light and transmitting 150Mhz carrier with 3 Khz of FM modulation you would hear it at 75Mhz with 1.5Khz Modulation. 

I think my math is correct.

Gary Gonnella W6RYO
http://www.w6ryo.com
AMSAT # 33687 


> -----Original Message-----
> From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
> Behalf Of Emily Clarke
> Sent: Friday, July 30, 2004 9:03 AM
> To: Brent Taylor; amsat-bb@AMSAT.Org
> Subject: Re: [amsat-bb] Doppler #2
> 
> 
> Speed of light or doppler would have nothing to do with it.  What 
> does make 
> the difference is that the modulation mode is FM, not AM/SSB.  If it was 
> AM/SSB then yes, doppler would have a huge effect.  FM is immune to this 
> (which is why FM users never hear stations that are "off 
> frequency",  sounding like mice.  The signal is either "captured" or it 
> isn't, and if it is, the modulation is always on frequency because the 
> discriminator can extract the information.
> 
> 73,
> 
> Emily
> 
> 
> 
> At 09:01 AM 7/30/2004 -0300, Brent Taylor wrote:
> >After sending out my first question, it dawned on me that, of 
> course, with
> >FM and with the speed of light, there is no way Doppler could affect the
> >frequency of the received tone.
> >
> >(heading for  a cold shower).
> >
> >Brent, VE1JH
> >FN66
> >----
> >Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> >Not an AMSAT member? Join now to support the amateur satellite program!
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> 
> 
> 
> ---------------------------------
> W0EEC - CM87tm
> AMSAT Area Coordinator - San Francisco Bay Area
> http://www.projectoscar.net    http://www.PlanetEmily.com 
> http://www.emilyshouse.com/experthams/ao7/
> 
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> ---------------------------------  
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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