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From: Fred Bloggs
User-Agent: Mozilla/5.0 (Windows; U; Win 9x 4.90; en-US; rv:1.0.1) Gecko/20020823 Netscape/7.0
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Subject: Re: How does a mixer work?
References: <firstname.lastname@example.org> <3DB2E3CE.email@example.com> <3DB2F22B.E856F6A4@webaccess.net> <3DB31A7C.firstname.lastname@example.org> <email@example.com>
Date: Sun, 20 Oct 2002 22:01:22 GMT
NNTP-Posting-Date: Sun, 20 Oct 2002 15:01:22 PDT
Organization: EarthLink Inc. -- http://www.EarthLink.net
Frank Bemelman wrote:
> "Fred Bloggs" schreef in bericht
>>Chuck Simmons wrote:
>>>What is the matter with the pot analogy? How the carrier amplitude is
>>>varied does not matter for generating AM. You can use a multiplier, you
>>>can vary the supply voltage to the last stage of amplification or you
>>>can use a pot. Your equations are fine no matter what method is used.
>>The pot wiper has a position , p, say that varies between 1 and 0, so
>>that the output is p x sin( Wc x t) at the output. The idea conveyed is
>>that p=p(t) is the information-bearing signal. This is not THE AM used
>>for communication. You would have to require that p(t)=0.5 x (1+ f(t)),
>>where |f(t)|<=1 is the information-bearing signal, and then you would
>>have conventional AM, where the modulation is only allowed to displace
>>the position from center-tap with zero mean. The modulation does not
>>shift the mean carrier amplitude as the brute-force pot analogy implies.
>>Now you can argue that the mean be included with the signal, but again
>>the convention is that information is transmitted by time-variation of
>>the transmitted waveform detectable characteristics.
> AM is AM. Modulation depth is irrelevant, who cares the pot gives upto
> 100% if desired, and 'THE AM' uses 50% (?) max. depth ?
Just think of AM for communication as chopper modulation. There is no
such thing as transmission of DC directly, it must be chopped or
translated or something else. Any information that varies at a rate
slower than the communication channel allows for the various forms of
receiver signal strength stabilization within its circuits is DC for
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