Jim, K9YC suggested some places to look that I hadn't thought of. When I turned off the "Flatten" option in the waterfall window, the noise bands went away. What I think is happening is that the algorithm in wsjt-x that flattens the response for the window sees the total lack of energy outside the K3's selected band and boosts the levels of the signals and noise near it as part of its compensation strategy.

73 Bill AE6JV

On 11/30/17 at 2:11 PM, [email protected] (Bill Frantz) wrote:

I have a K3 which has been upgraded to have the Elecraft internal USB sound 
card.

I tried adjusting the DSP bandwidth when running FT8 to eliminate a strong signal above the FT8 subband and noticed that there was a strong noise bar on the water fall for about 400 Hz below the high cutoff. Further playing with the controls showed a similar noise bar just above the low cutoff. Note that these noise bars are in the requested pass band.

Has anyone else observed this noise? Does anyone have an explanation?

73 Bill AE6JV

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Bill Frantz        | Truth and love must prevail  | Periwinkle
(408)356-8506 | over lies and hate. | 16345 Englewood Ave www.pwpconsult.com | - Vaclav Havel | Los Gatos, CA 95032

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