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From: firstname.lastname@example.org (Asa Cannell)
Subject: Re: How does a mixer work?
Date: 17 Oct 2002 08:10:40 -0700
NNTP-Posting-Date: 17 Oct 2002 15:10:41 GMT
Okay now I get the multiply part, where the LO is driven hard,
multiply the RF/IF input by 1 or 0. But why do we need non-linear
elements? I understand if you apply two signals to a linear element
you just get to signals. But I dont see why a non linear element
suddenly multiplies. Is there some analogy or other type of circuit
that uses the non linear aspect of diodes in the same or similar way?
"Alfred Lorona" wrote in message news:...
> "Asa Cannell" wrote in message
> > How does a mixer work? I don't understand why it needs a non-linear
> > element. I think examples of why a linear element (resistor) wont work
> > would help illustrate why a non-linear element (diode) will. Also,
> > what does 'mutiply' mean in terms of mixing? What if two DC signals
> > are applied to a mixer, like 2V and 4V? Will the output be 8V?
> > (multiply).
> > Thanks,
> > Asa
> If you apply a 10 hertz and a 15 hertz signal to a resistor all you can
> expect as output is a 10 hertz signal and a 15 hertz signal. In a mixer, the
> idea is to obtain the difference between the two frequencies which is 5
> hertz and the sum of the two frequencies which is 25 hertz at the output.
> The output will also contain the two original frequencies of 10 and 15
> hertz. The useful, or desired, output signal is either the sum or the
> difference frequency. All of the others are filtered out and only the
> desired frequency is allowed to pass through to the rest of the circuitry.
> You can only obtain the sum and difference frequencies in a non linear
> circuit element. That is why a resistor, being a linear circuit element,
> won't do the job.
> The correct technical term for the mixing process in a mixer is called
> 'multiplication' but this sometimes confuses people such as you indicate
> with your example of the two DC voltages. Hi.
> Until you gain a more detailed idea of the mixing process, it may help to
> just think of a mixer as a 'distorting' device that generates frequencies at
> the output that are not present at the input . This is what distorting
> devices do.
> A diode is a non linear circuit element and that is why it makes a good
> mixer and is widely used in inexpensive AM radios.
> No, mixers do not work with DC input signals.
> 73. AL
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