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Complex AM demodulation- simple question

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konradb

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To demodulate AM, I use the formula am = sqrt(I*I + Q*Q)

I am mixing an AM IF signal to baseband, i.e. carrier plus 2 sidebands. My test signal is modulated at 800Hz.

When I look at the demodulation, it looks OK when I mix perfectly to 0Hz, but as the transmitted signal moves up or down frequency, I end up with 2 frequencies in the demodulated signal.
i.e. I get a demodulated signal of 200Hz and 600Hz when the carrier is at 200Hz.

Is what I am seeing correct or have I got some other mixing products from somewhere?

regards
Konrad
 

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