Weird Waterfall Display when transmitting on CW

Hi Mark, with the 6400, you only have one Spectral Capture Unit (SCU). That means that when you have both slices open on harmonically related bands (like 40 and 20), the 3rd order filtering has to be disengaged so that you can hear on both bands simultaneously. Note that the word "Wide" appears in the upper right hand corner of SmartSDR to indicate this situation.

What you are seeing on 20, is the second harmonic of your 40 meter signal. While the Flex has a really clean signal, no transmitter or receiver is perfect, and that is what you are seeing. If you had a 6600 or 6700 with two SCUs, then the bandpass filtering could stay in place if ANT1 was on one band and ANT2 was on the other (i.e. not in Wide mode) and you would not likely see this phenomenon (or it would be greatly reduced).

If you take your 6400 to Field Day where there are other transmitters close by, you will want to be sure to not run in Wide mode, or the harmonics or fundamental overload from other transmitters will likely get in your way.

A couple of years ago my buddy Dave and I each ran a Flex 6400 within 150 yards of each other during Field Day and could not hear each other at all until we were on the same band, and usually only when on the same segment (e.g. CW, SSB). That was because we did not have multiple bands open at the same time, and therefore were not in Wide mode.

So, bottom line is that you are not transmitting on two bands at once, you have just opened up your receiver's passband and are interfering with yourself a bit.