In article ,
Cecil Moore wrote:

Quoting my 1957 ARRL Handbook: "Narrow-band f.m. or p.m.,
the only type that is authorized for use on the lower
frequencies where the phone bands are crowded, is defined
as f.m. or p.m. that does not occupy a wider channel than
an a.m. signal having the same audio modulating frequencies.
Narrow-band operation requires using a relatively small
modulation index." It goes on to say a modulation index
of 0.6 is about optimum for those conditions.

Is NBFM still allowed?

I read through the current Part 97 regs a few months ago, and
concluded that it is. See 97.305 (Authorized Emission Types), and
97.307 (f) (1).

The current standard allows a modulation index of up to 1, at the
highest modulating frequency. This applies to all angle-modulation
modes (PM and FM).

The rules aren't specifically worded as "f.m. or p.m. that does not
occupy a wider channel than an a.m. signal having the same audio
modulating frequencies" these days - the restrictions are in terms of
the modulation index, and the general requirement that one not use
"more bandwidth than necessary for the information rate and emission
type being transmitted, in accordance with good amateur practice."

I don't recall having run across any narrowband FM on the HF bands...
I think there are still a few 10-meter repeaters operating around the
country somewhere, but FM HF simplex seems to be either completely
dead, or used just by occasional experimenters.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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