#### DD4WH

##### Well-known member

Hi Mike,

filtering with FIR filters in the time domain is very inefficient when it comes to large filter sizes (= steep filters). It is much more efficient to filter in the frequency domain, which involves an FFT, a complex multiply with a filter mask and an inverse FFT. That process is called Fast Convolution.

In the context of the Teensy Convolution SDR, its all explained here:

https://github.com/DD4WH/Teensy-ConvolutionSDR/raw/master/Teensy Convolution SDR english.pdf

Also you could have a look at the excellent paper by Borgerding referenced in Wikipedia:

https://en.wikipedia.org/wiki/Overlap–save_method

Youngblood has published a nice paper in 2002:

http://www.arrl.org/files/file/Technology/tis/info/pdf/020708qex013.pdf

One side effect of using Convolution filtering in an SDR is that you do not even have to demodulate SSB at all, because the sideband suppression is already done in the filter (of course, you have to choose your filter bandwidth in the right way for LSB/USB) .

Have fun with the Teensy Convolution SDR,

Frank

filtering with FIR filters in the time domain is very inefficient when it comes to large filter sizes (= steep filters). It is much more efficient to filter in the frequency domain, which involves an FFT, a complex multiply with a filter mask and an inverse FFT. That process is called Fast Convolution.

In the context of the Teensy Convolution SDR, its all explained here:

https://github.com/DD4WH/Teensy-ConvolutionSDR/raw/master/Teensy Convolution SDR english.pdf

Also you could have a look at the excellent paper by Borgerding referenced in Wikipedia:

https://en.wikipedia.org/wiki/Overlap–save_method

Youngblood has published a nice paper in 2002:

http://www.arrl.org/files/file/Technology/tis/info/pdf/020708qex013.pdf

One side effect of using Convolution filtering in an SDR is that you do not even have to demodulate SSB at all, because the sideband suppression is already done in the filter (of course, you have to choose your filter bandwidth in the right way for LSB/USB) .

Have fun with the Teensy Convolution SDR,

Frank

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