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From: "Daniel A. Krantz" <dkrantz@dakran.com>
Subject: Re: AM Vs FM in Aeronautical Band
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It is the frequency, not the modulation, that determines whether a signal is
line-of-sight, or will bounce off layers in the Ionisphere.  You are confusing
commercial radio, where FM uses VHF frequencies, and AM uses much lower
frequencies, with aircraft radios, which use VHF with AM modulation.  For a given
frequency, whether the signal is modulated using AM or FM should not affect the
range very much, if at all.

Dan Krantz

NAv8or wrote:

> Basic physics:  Higher frequency waves require greater propagation energies,
> and therefore will not travel as far as will lower frequency waves, given the
> same transmitter power.
>
> Therefore, AM will outtravel FM if it is not interfered with.
>
> OTOH, higher frequency waves containing more energy, they will do better at
> burning through interference, which is why military all-weather aircraft tend
> to rely more on UHF than VHF.
>
> If you doubt this, look at VOR vs TACAN range.  VOR can generally be received
> at greater distance.  And HF radios have tremendous ranges... between wave
> travel and atmospheric ducting, I've been on a P-3 out of Jacksonville
> conducting a conversation with an HF operator in Newfoundland.
>
> Nav8or



