Re: AM/FM on one carrier
- From: John Larkin <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 14 Jun 2005 07:55:14 -0700
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. 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.
John
.
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