[amsat-bb] Doppler shift question

Noel Petit petitnoel47 at gmail.com
Thu Jun 6 14:37:55 UTC 2019

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).

Noel Petit - WB0VGI

On 6/6/2019 8:51 AM, Dave Webb KB1PVH via AMSAT-BB wrote:
> I'm pretty sure the reasons for AM in aviation was because equipment was
> cheap and easy to build when the aviation band was formed and if 2 stations
> doubled they would both be heard.
>   My guess for not not having perceived doppler in aviation is because
> aircraft aren't flying at 17,500mph and they are using VHF frequencies.
> Feel free to contact me if I'm wrong.
> Dave-KB1PVH
> Sent from my Galaxy S9
> On Thu, Jun 6, 2019, 8:44 AM KC9SGV via AMSAT-BB <amsat-bb at amsat.org> wrote:
>> More train Doppler effect.
>> These are sound waves, but the RF FM principle is the same.
>> Not sure why they don't use AM in space, like in aviation...I.e. NO
>> Doppler effect.
>> https://youtu.be/fWX38qjECyE
>> Sent from my iPad
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