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From: Fred Bloggs
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Subject: Re: How does a mixer work?
References: <email@example.com> <3DB2E3CE.firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <3DB34C15.5203CF0@webaccess.net> <3DB37C55.6F63@Spam.Bots> <3DB36A58.4E49CEAC@webaccess.net> <3DB5324F.email@example.com>
Date: Tue, 22 Oct 2002 12:00:46 GMT
NNTP-Posting-Date: Tue, 22 Oct 2002 05:00:46 PDT
Organization: EarthLink Inc. -- http://www.EarthLink.net
Kevin Aylward wrote:
> "Fred Bloggs" wrote in message
>>Chuck Simmons wrote:
>>>At this point I take a stand against the hidebound conventionalism
>>>is the application of mathematics to engineering. I am very
> sensitive to
>>>this because I have no engineering education whatever and ALL
>>>mathematical statements engineers make can be considered suspect
>>>of the hidebound conventionalism.
>>>Consider the equation:
>>>This is really an identity. The left hand side says that the carrier
>>>varies in amplitude according the the operations on the field of
>>>numbers. The second says that, fully equivalently, there are three
>>>constant frequencies and amplitudes.
>>>It is pure hidebound conventionalism that says that though the two
>>>of the equation are correct, the right hand side is more correct.
>>>mathematical hogwash. There can be no justification for that sort of
>>If the early developers adopted your perspective, there would be no
> I do actually remember some stories like this, vaguely. Apparently,
> people were sceptical that sidebands were real, and that if you had a
> really sharp filter you could still recover the modulation. This was, I
> understand even experimentally "proven". In reality, they just did not
> use a sharp enough filter.
They were actually dealing with entities with too sharp a characteristic
such as the tuned stages and the antenna. It was recognized early on
that the modulation spectral spread had to be a very small percentage of
the carrier for distortion-free communication. They also discovered that
a really sharp filter could not recover the sideband by peak detection.
The carrier had to be "restored" first. The product detector was then
developed which does the restoration and detection in one step-including
a simple low pass. You have the sideband sin((Wc+Wm)t) for example, and
the product with restored carrier is sin(Wct)*sin((Wc+Wm)t) which is
actually 0.5*( cos(Wmt)-cos( (2*Wc+Wm)t)), an easy job for a lowpass to
extract cos(Wmt). The tradeoff was the added complexity of automatic
frequency control, AFC, for carrier restoration, but this was easily
handled, and a small price to pay for the benefit of SSB such as better
S/N, greater range, and less transmission power to do the same job.
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