[R-390] Filters

[Charles P. Steinmetz]

John wrote:

>Anyhow, you folks have my curiosity up about the software 
>requirements to do a DSP filter suitable for Collins mechanical 
>filter replacement.  Can some of you gurus point me to where the 
>math algorithms are defined?  Gotta be on the web someplace

For the software, start with Hayward, et al., Experimental Methods in 
RF Design and then move to dedicated DSP texts.

The software isn't the problem -- processing horsepower 
is.  Digitizing and manipulating 455 kHz with sufficient bit depth is 
still close to cutting edge.  Most DSP radios use a final IF in the 
12-20 kHz range, and even that is taxing to process in real 
time.  This is not a job you can do with microcontrollers.

But my previous question still stands -- once you have developed the 
DSP capacity to do the filtering, why in the world would you convert 
back to analog and put it through the 390A IF?  It would be plain 
silly not to have the DSP also handle AGC, passband shift, notch 
filtering, noise blanking, all-mode detectors, and synchronous AM, at 
the least.

Best regards,

Charles