While setting up for the AWA '29 QSO Party I started playing more with the KX3 filtering and audio response....mostly because 80 meters seemed particularly noisy that night. I found something that really helped me see the interaction of the various receive selectivity options: Rcv Audio Equalization, Notch, APF, Data/RTTY mode, Passband Width, Passband Shift and Passband Hi/Low Cut.
I downloaded DigiPan from
http://www.digipan.net/ (Freeware) onto my laptop, not for the PSK31
function but for the waterfall. I then configured DigiPan to use my
laptop built-in mic as the audio input/source. With my laptop sitting
next to my KX3 I tuned to a unpopulated but white noisy frequency. This may require the preamp to be turned on. While
watching the white noise on the DigiPan waterfall I tweaked the various
filter settings. The white noise waterfall display changes to reflect
the filter settings, clearly showing me the impact of what I was doing.
SSB, CW and data signals can even be tuned in and viewed as the various
selectivity options are changed. The KX3 CWT Aid and the Filter Passband Graphic show some of this but not to the detail of the DigiPan waterfall.
For example here's a sample waterfall showing the impact of narrowing the KX3 bandwidth setting followed by adding the Audio Peak Filter (APF). The horizontal scale is frequency (in Hz) and time is the vertical scale. The CW signal of interest is the yellow streak at 520Hz. Interference is the yellow (stronger) and blue (weaker) around the 520Hz signal.