Why don't voice radio communications use FM?

"Mxsmanic" wrote in message
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Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio?


Wouldn't that reduce the available frequencies?

Yeah, Steve, it would. But I think we might be able to swap (on a long term
swap basis) the VHF com band for stuff up between 600 and 900 MHz. that have
very limited usage. Not only could we get way more bandwidth, but the
antenna size is cut by a factor of 6 or so.

Jim


"Steven P. McNicoll" wrote in message
nk.net...

"Mxsmanic" wrote in message
news

Perhaps this is a naive question, but: Why don't voice radio
communications for aviation use FM radio instead of AM radio?


Wouldn't that reduce the available frequencies?

Steven P. McNicoll writes:

Wouldn't that reduce the available frequencies?

For a given audio bandwidth, FM tends to require somewhat more radio
bandwidth, as I recall, but the audio bandwidth of aviation radio is
already so limited that I don't think this would be an issue. The
gain in clarity would outweigh any loss of audio fidelity, assuming
that the same channel widths were used.

If frequencies were reallocated (instead of allocating new ones), that
would be different. That would also obsolete older equipment much
more quickly, which might not be acceptable. But there must be some
space somewhere that could be added to the frequencies, or perhaps
some band so rarely used that it could be reassigned.

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You recall incorrectly.

Jim


"Mxsmanic" wrote in message
...
Steven P. McNicoll writes:

Wouldn't that reduce the available frequencies?

For a given audio bandwidth, FM tends to require somewhat more radio
bandwidth, as I recall,

RST Engineering writes:

You recall incorrectly.

Perhaps. Theoretically it should require exactly the same bandwidth,
but I seem to recall reading that typical implementations used more
bandwidth. In any case, you don't need much for voice communication.
The advantage of FM would be the reduction of noise. Digital over FM
would be still better.

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