From: Don Pearce
Subject: Re: How does a mixer work?
Date: Wed, 23 Oct 2002 07:43:49 +0430
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On Tue, 22 Oct 2002 12:00:49 GMT, James Meyer
>On Tue, 22 Oct 2002 08:15:03 +0430, Don Pearce
>>On Sun, 20 Oct 2002 23:32:09 GMT, Jim Thompson
>>>In classic AM modulation:
>>>The carrier amplitude is CONSTANT irrespective of the value "M".
>>> ...Jim Thompson
>>JIm, this is semantics taken to a rather strange degree. This argument
>>would claim that the attenuator on a signal generator does not change
>>the level of the signal it produces - merely adds sidebands.
> If you take the period of time from a little before the attenuator is
>switched to a little after the attenuator has established a new amplitude, then
>you will find that sidebands HAVE been generated by the switching.
> The sidebands are always there. Before the switching, the sidebands are
>not removed in frequency from the carrier. They aren't after the switching
>either. But DURING the switching, they certainly exist. The faster the
>switching occurs, the more removed from the carrier they are.
No, the position we have here is that the amplitude never changes.
That would presuppose that every signal source ever made has been
anticipated back to the dawn of time - and will continue in existence
out to infinity. This is a consequence of Fourier analysis of a
signal. It is clearly, in physical terms, a nonsense. Yet Fourier
analysis is still a useful tool. It must be seen as no more than that,
though, and we shouldn't be extrapolating too far beyond its