[Elecraft] APF For K3: progress report

[Wayne Burdick]

We might have a field-test revision of K3 code that includes APF  
sometime this week.

In this test version, APF is turned on by rotating the WIDTH control  
counterclockwise past the 50-Hz setting ("BW 0.05") to the 30-Hz APF  
setting ("APF 0.03"). This eliminates the need for a menu entry or a  
new switch function. A new DSP graphic pattern shows that APF is in  
effect. SHIFT can be used, with either 10- or 50-Hz steps.

The APF filter is an "IIR" (infinite impulse response) DSP filter that  
accurately emulates the equivalent analog circuitry. There's a slight  
ring to the filter, as expected. Gain is also increased when APF is  
turned on, compensating for the loss of overall signal+noise that  
occurs at this very narrow bandwidth.

73,
Wayne
N6KR