[Milsurplus] AI response to Jack Antonio’s request on FM v AM in aircraft.

[Brenda Gentry]

Years ago, I asked why AM instead of FM for air traffic. Because of FM's 
capture effect, one transmitter could obliterate another at a critical 
moment. If two or more transmit at the same time on AM, they will be 
heard even if there is a pile-up. There is also likely to be a 
heterodyne beat. These will alert everyone that a pileup is occurring 
and every person transmitting must repeat their messages in proper turn 
and sort it out.

    B.Gentry, KA2IVY

On 7/30/25 8:04 PM, hwhall--- via Milsurplus wrote:
> AI doesn't always know what it's talking about. I've gotten some funny answers from it. And it can also invent info that doesn't actually exist (AI "hallucinations").  Offhand, I think I doubt that aircraft speed within the bounds of atmospheric craft can induce enough doppler to alter the modulation of voice communications. Doppler doesn't change quickly compared to the rate of changes in a voice modulated FM signal. Doppler would mostly appear as a slight shift in apparent "carrier" frequency, wouldn't it?
>
> Wayne
> WB4OGM
>
> On Wednesday, July 30, 2025 at 12:24:50 PM MDT, boeing377 at gmail.com <boeing377 at gmail.com> wrote:
>
> FM systems in high-speed or maneuvering aircraft can be affected by Doppler-induced phase and frequency shifts, especially when the aircraft is moving relative to the transmitter or rapidly changing direction. While most open-source discussions focus on FM capture effect and baseband modulation, there’s real engineering literature out there that addresses Doppler effects on FM signal coherence, phase noise, and demodulation fidelity — particularly in the context of military aviation, missiles, and radar.
>
> 📚 Where to Look:................
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