Welcome to the new FlexRadio Community! Please review the new Community Rules and other important new Community information on the Message Board.
If you are having a problem, please refer to the product documentation or check the Help Center for known solutions.
Need technical support from FlexRadio? It's as simple as Creating a HelpDesk ticket.

Weird Waterfall Display when transmitting on CW

I have a 6400M. I am on 40 meters and my Transmit frequency is 7.016.5. I currently have 2 slices open. A is 40 Meters and B is 20 Meters. When I sent my call on 40 meters, I notice that on the Slice B, 14.033 that something seems to be showing that my transmit signal is on that band also. Even though I am not transmitting split. What would be causing something like this. I just noticed this tonight.

Mark Griffin, KB3Z


  • KD0RC
    KD0RC Member, Super Elmer Moderator

    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.

  • K0FLY
    K0FLY Member ✭✭✭


    Slice B is hearing the second harmonic of your transmitter.

    Gayle K0FLY

  • Mark Griffin
    Mark Griffin Member ✭✭

    Thanks Guys. This is the first time I have had a radio where I could see 2 different slices at the same time.

    Mark KB3Z

Leave a Comment

Rich Text Editor. To edit a paragraph's style, hit tab to get to the paragraph menu. From there you will be able to pick one style. Nothing defaults to paragraph. An inline formatting menu will show up when you select text. Hit tab to get into that menu. Some elements, such as rich link embeds, images, loading indicators, and error messages may get inserted into the editor. You may navigate to these using the arrow keys inside of the editor and delete them with the delete or backspace key.