On 6/30/07 7:43 PM, in article cv3e8313dio3rso4a9st24thkrgam0761n@4ax.com,
"Jeff Liebermann" <jeffl@cruzio.com> wrote:

> Radium <glucegen1@gmail.com> hath wroth:
>
>> On Jun 30, 3:46 pm, Jeff Liebermann <j...@cruzio.com> wrote:
>>
>>> With AM, it's ALWAYS the high frequency
>>> that acts as the carrier
>>> and the lower that acts as the modulation.
>
>> In AM, isn't the carrier the signal which always maintains a constant
>> frequency and only varies by amplitude?
>
> You really are clueless. The carrier does NOT vary in amplitude. If
> it did, that would be modulating the carrier, which is the job of the
> modulator, not whatever is producing the carrier. You could have two
> modulators in series, that would make the circuit overly complicated.
> Please re-read my highly simplified previous explanation about the
> symmetry of the AM multiplier (mixer) input ports until it's absorbed
> and understood by your porous brain.
>
> Incidentally, the reason I keep using the term "multiplier (mixer)" is
> to avoid confusion with a harmonic multiplier. An AM modulator is a
> mixer, not a harmonic multiplier.
>
> Also, the carrier might remain constant frequency, for a given FCC
> channel assignment, but the modulation is all over the place. For
> example, your voice goes from 300 to 3000Hz, all of which is fed to
> the modulator for digestion.
>
> Conventional TV is VSB (visidual side band) which is a form of AM with
> one of the two side bands partially removed, usually by filtering.
> There's a carrier 1.25MHz offset for the video, another carrier 4.5Mhz
> offset for the audio, and whatever else they can throw in for low
> speed data. Two more more carriers are required for TV+audio.
>
> If you want to get really high-techy, the new digital modes (DRM,
> iBiquity, HD Radio, etc) all have multiple carriers, each of which is
> modulated individually. Same with various OFDM modes, which have
> multiple carriers, individually modulated and positioned orthogonally
> from each other to prevent mutual interference from adjacent modulated
> carriers.
>
>> If a carrier signal varies by anything other than just amplitude, then
>> it isn't AM. Right?
>
> Wrong. The carrier can also vary, such as in a sweep generator or
> jammer. It's not commonly done but it's possible. Want to obliterate
> the entire AM broadcast band? No problem. Just sweep the carrier
> from 530KHz to 1650KHz, while modulating the 300 to 3000Hz audio with
> a rendition of your incoherent ranting.
>
> By the way, you're welcome.
>


You are getting far afield of classical AM, which is the subject of Radium's
post. He is confused and you aren't helping.