[amsat-bb] Doppler shift question

Zach Metzinger zmetzing at pobox.com
Thu Jun 6 15:53:52 UTC 2019

On 2019-06-06 09:37, Noel Petit via AMSAT-BB wrote:
> the other reason to stick with AM is that you can hear if other stations 
> are trying to break in. FM has capture and blocks all but the strongest 
> station. AM can superimpose multiple signals and hear if emergency calls 
> may be made. Additionally, in the '30's FM was nearly impossible to 
> generate reliably. AM doesn't depend on the transmitter's stability (to 
> an extent).

On linear transponder satellites 
(https://www.amsat.org/two-way-satellites/), you _can_ hear other 
stations doubling.

AM is wasteful of power, as others have commented, and has no place on a 
power-limited satellite. The carrier, containing no information, 
consumes 2/3rds of the transmitted power. The rest of the power is split 
between two sidebands carrying the exact same information. 

I disagree strongly with your assertion that FM was "nearly impossible" 
to generate. (https://en.wikipedia.org/wiki/Armstrong_phase_modulator)

--- Zach

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