Re: AM/FM on one carrier

"John Larkin" <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote
in message news:6irta1p3g1nlsddu7s591m2pekqtuqdiv8@xxxxxxxxxx
> On Mon, 13 Jun 2005 20:42:04 -0700, "Larry Brasfield"
> <donotspam_larry_brasfield@xxxxxxxxxxx> wrote:
>
>>"Don Bowey" <dbowey@xxxxxxxxxxx> wrote in message news:BED39AE3.5A21%dbowey@xxxxxxxxxxxxxx
>>> On 6/13/05 4:24 PM, in article lp4sa155402uh70aen5m09h85lho9okqvg@xxxxxxx,
>>> "John Fields" <jfields@xxxxxxxxxxxxxxxxxxxxx> wrote:
>>>
>>>> Since the amplitude of the carrier will be varying because of the AM
>>>> and
>>>
>>> Tjhat is not correct. The carrier amplitude is constant with modulation.
>>
>>If the carrier amplitude is constant, it is not being amplitude modulated.
>>This is so obvious as to be tautological. "AM" = "amplitude modulation".
>
> If you define "carrier" as the amplitude of the central spectral line,
> excluding the sidebands, then an AM carrier is constant irrespective
> of AM modulation.

You are mixing domains here. "Constant" refers to a time
domain concept. "Spectral line" refers to a frequency
domain concept. If you are saying the set of AM spectra
starting with the same unmodulated carrier all have the
same line height at the carrier frequency, I would agree
with an exception for the results of DC modulations.

> The carrier amplitude of an FM signal varies with
> modulation index according to a Bessel function, and has nulls at
> various points.
>
> So if you FM modulate a carrier with the right sinewave signal at the
> right deviation, the carrier disappears completely, which has got to
> confuse an AM detector.
>
> I'm guessing that AM and FM modulation can be used fairly orthogonally
> at very low modulation levels.

Sure. The crux is how low the modulation
levels need to be given the OP's requirement
and receiver attributes.

--
--Larry Brasfield
email: donotspam_larry_brasfield@xxxxxxxxxxx
Above views may belong only to me.


.

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