[Elecraft] K3 problem with distorted audio on AM receive

[Frank R. Oppedijk]

Guys,

I'm experiencing a strange behavior on AM receive of strong 
medium-wave broadcast stations. My K3 is equipped with the FM roofing 
filter in the FL1 position. It uses this filter for AM receive.

Before the problem occurred, I had set VFO A to 1.008 kHz by direct 
frequency entry. There's a strong (S-9+40 dB) broadcast station 
there. At that moment the sound quality was  good. Then I moved the 
VFO A dial a couple of kHz and then moved back. This led to the audio 
becoming very distorted. I could only undo the distortion by 
re-loading firmware. (I've noticed this problem with the 2.63 
firmware, but I see it also with the 2.58 amd 2.45 versions...)

Some further investigation learned me that the amount that I can move 
VFO A before the problem starts occurring depends on the settings of 
the DSP filter:

(1) With LO=0.00, HI=3.00, FC=1.50 and BW=6.00, the problem occurs as 
soon as move VFO A more then 2.0 kHz from the start frequency of 1.008 kHz.
(2) With LO=0.00, HI=2.95, FC=0.45 and BW=10.00, the problem occurs 
as soon as move VFO A more then 0.90 kHz from the start frequency of 1.008 kHz.

Has anyone else experienced this? Any ideas as to the cause of it?

73,

Frank PA4N

P.S. Another strange thing, that may or may not be related and which 
I don't understand: why isn't the DSP BW value displayed equal to HI 
- LO ? Can anyone enlighten me?