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Help identify filter type

Started by Vinzz 6 months ago6 replieslatest reply 6 months ago170 views

I have a software filter that multiplies the input signal with a sine and cosine wave (I,Q). After multiply the complex output is square rooted to get the amplitude.

What would be the name of this kind of filter?

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Reply by neiroberJanuary 4, 2024

Hi Vinzz,

What you are describing is not a filter.  The multiplication by sine and cosine of frequency f0 is called quadrature conversion.  It converts a signal centered at frequency f0 to a complex baseband ("I/Q" or "I + jQ") signal.

To get the amplitude, you take the square root of I^2 + Q^2.

regards,

Neil


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Reply by VinzzJanuary 4, 2024

If that is the case then the frequency of the sine and cosine would be irrelevant?

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Reply by SlartibartfastJanuary 4, 2024

The frequency of the sine wave (aka, local oscillator, in a tuning application) determines which frequency gets mixed (translated) to baseband (DC, zero frequency).   That's how a radio tuner functions.

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Reply by neiroberJanuary 4, 2024

Vinzz,

Try looking up "quadrature down-converter" in a textbook or online.

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Reply by SlartibartfastJanuary 4, 2024

+1 that that's a mixer followed by an amplitude detector.   What you're describing is a tuner and a demodulator for AM radio.

Usually that does include a filter, but the process you described didn't include one.

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Reply by chalilJanuary 4, 2024

If I understand your description correctly, you are finding the envelop of the signal. kind of Hilbert Transform usecase...