[Elecraft] K4 CW filtering

[Bill Overstreet]

I need some explanation of how filtering is done in the K4 when in the 
CW mode.

As a comparison, when in LSB mode with 2.2 kHz BW, I can copy CW but it 
is obvious that the full 2.2 kHz bandwidth is available.

Then, switching to CW mode (with APF off and filter BW set to 2.2 kHz) 
there is a significantly restricted bandwidth when compared to the LSB 
filtering.

I thought maybe the CW IIR filter was in play, but I turning it off, 
there is no noticeable effect.

There must be some additional filtering in the receiver chain when in 
the CW mode, but I don’t understand what its characteristics are. Or 
whether can it be turned off or not?

Receiver performance in the CW mode is definitely better, but I would 
like to understand the filter arrangement in the K4.

In general, a technical "theory of operation" manual would be helpful.

Thanks, Bill, K4AJ