[Elecraft] here is how to "get a feel" for a roofing filter

[Lyle Johnson]

Hello Brett!

> Is there no way to put dsp at/as the first filter?
> What are the limitations of the dsp, frequency, filter quality?
> Is there a problem getting dsp to work at say 455 khz?

To answer these questions would take a textbook!  Or at least a very 
long essay.

The short version is: there are many ways to design a radio, and to 
partition the analog and digital circuitry.  We chose a design 
architecture that provides world-class performance at a realistic cost.

> What would be the result of a real good variable filter
> at the 8.215 Mhz IF just after the mixer and NO dsp
> for filtering? (K2?)

It would be a K2 without the KDSP2 :-)

> The 2nd IF of 15 khz is audio, is it not?

The use of a final IF in the 12 kHz to 40 kHz range is used by virtually 
every manufacturer of DSP-equipped radios.  There are solid technical 
and economic reasons for this.

73,

Lyle KK7P