[Elecraft] K3 DSP shape factor?

[Lyle Johnson]

> The question I have is "What is the effective shape factor of the K3 
> DSP?"

DSP filters usually are so-called Finite Impulse Response (FIR).  FIR 
filters for a given complexity (length) have a nearly constant 
transition region width going from the passband to the stopband.  For 
this reason, "shape factor" varies depending on the width of the filter. 
  ( It also depends on the ultimate attenuation required, and the 
"windowing function" applied to deal with of the "Gibb's phenomenon" and...)

The following is just an illustration.

Let's say that the transition band for a set of FIR filters from 6 dB to 
60 dB is 150 Hz.  [ This number happens to be from a quick check I just 
did on a dialed-in filter width of 500 Hz, and a center of 600 Hz on my 
K3.  This is using a 2.8 kHz roofing filter, AGC OFF, internal AFV and 
dBV function, and signal level at the threshold of hardware AGC action. 
   Yes, I tuned to the higher pitch side to make the measurement :-) How 
to do all of this is left as an exercise for the reader. ]

If the 6 dB width is 500 Hz, then the 60 dB width is (150+500+150 =) 800 
Hz and the "shape factor" is 1.6:1.

If the 6 dB width is 2400 Hz, then the 60 dB width is (150+2400+150 =) 
2700 Hz and the "shape factor" is 1.125:1.

YMMV, and all is subject to change at the whim of the firmware writers :-)

73,

Lyle KK7P