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There is an old but best way to do variable bandwidth. Here is how it works :

You take two crystal filters of, let's say 1 KHz bandwidth at two slightly off frequncies, let's say 12 Mhz and 11 MHz. Now place a mixer between them both, fed from a variable oscillator, in this case of 1 MHz.

Now, only when the oscillator is exactly a 1 Mhz, the the signal of 1Khz bandwidth will make it through. If you shift the frequency of the oscillator the skirts of each of the filter will move closer or away from each other. This is better than anything DSP can offer, it is completely analog too.

- f

On Sat, Mar 11, 2017 at 10:34 AM, John VA7JBE via Groups.Io <va7jbe@...> wrote:

I plan to use a variable bandwidth digital filter from SOTABEAMS () with my uBitX, which has an adjustable bandwidth (and passband) of 200Hz-3500Hz.? This allows a lot of flexibility in regards to picking out CW signals and cleaning up SSB audio on congested parts of the spectrum. I haven't calculated the bandwidth of the crystal filter described in the schematic, but if it is very narrow I may end up retooling it and letting the audio filter do most of the grunt work. Ironically the digital filter would probably end up costing more than the uBitX itself!