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Subject: Re: How does a mixer work?
References: <3DB2E3CE.firstname.lastname@example.org> <email@example.com> <3DB41488.firstname.lastname@example.org>
Organization: The Armory
X-Newsreader: trn 4.0-test69 (20 September 1998)
From: email@example.com (Richard Steven Walz)
Date: 22 Oct 2002 05:33:23 GMT
In article <3DB41488.firstname.lastname@example.org>, Fred Bloggs wrote:
>John Fields wrote:
>> On Sun, 20 Oct 2002 17:11:22 GMT, Fred Bloggs
>>>>Don Pearce wrote:
>>>>You are still assuming incorrectly that the Carrier of an AM signal
>>>>modulation. It does NOT; the carrier amplitude is easily proved to
>>>>with correct levels of modulation. In your experiment you are varying the
>>>>amplitude of the carrier and that is not an AM signal.
>> The incorrect assumption is yours. If there was no variation in the
>> amplitude of the carrier when it was being modulated what would you
>> postulate would be the mechanism involved in generating the
>> sidebands? It's called Amplitude Modulation for a reason, I
>> believe, that reason being that the carrier amplitude is caused to
>> vary by the modulating source.
>> Perhaps what you're thinking about is the _average_ (instead of the
>> instantaneous) amplitude of the carrier, which doesn't vary with
>> modulation, since the peaks and the valleys average out. Consider
>> the case of 100% modulation, for instance. With no modulating
>> source the carrier amplitude will be at some nominal value, while
>> with the modulating source at a minima the amplitude of the carrier
>> will be zero, while with the modulating source at a maxima the
>> amplitude of the carrier will be twice what it is in the quiescent
>>>Right, AM is usually of the form (1+cos(Wm x t))* sin(Wc x t) and this
>>>expands to sin(Wc x t) + [sin( (Wc+Wm) x t) + sin( (Wc-Wm) x t)]/2 which
>>>is easily recognized as the carrier, of constant amplitude, and two
>>>sidebands displaced from carrier by Wm, and this is exactly how AM is
>>>implemented. So, you are right, the pot analogy is hopelessly flawed.
>> The pot analogy is perfect and is precisely _how_ AM is generated.
>> _You've_ also fallen into the trap of looking at average instead of
>> instantaneous carrier amplitude during _amplitude_ modulation. As
>> I noted previously, if the amplitude of the carrier wasn't varied
>> there would be no way to impress information on it with the
>> resultant sidebands being generated. We're taking AM here, Bloggsy,
>> not FM or PM or any other kind of M, so don't try to wiggle out of
>> it, you're just _wrong_. Own up to it.
>> John Fields
>> Professional circuit designer
>You're a dumbass who knows absolutely nothing about frequency analysis
>of any kind. The AM equation is clear to anyone with even a second year
>level of engineering education in Fourier analysis- which you do not
Gee, even if HE didn't, *I* do, and YOU'RE WRONG!
>The composite signal consists of a constant amplitude carrier
>with sidebands on either side displaced by the center frequency of the
>bandlimited modulation function.
Do you even KNOW that such a signal IS produced by a pot-like circuit of
which he is speaking??? It *IS*!
>It's a sorry commentary on your
>pathetic level of development that after 40 years you still do not
>comprehend the idea of superposition.
We understand superposition, but you simply don't grasp all the ways
that such a superposition CAN be achieved! Simple variation of a POT
across a carrier CAN INDEED DO IT *PERFECTLY*!
Lots of people fall into the same trap as you did, they simply will not
conceive that something as apparently complex as the sidebands of a complex
signal can be produced simply by the process of dialing a knob!! BUT THEY
CAN AND ARE!
>Well why would you? Your work
>experience has required absolutely nothing beyond the most basic hands on-)
I'm a physicist, he knows what he's talking about, and you're blathering
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