How do you properly interpret SSB signals shown on the waterfall?

Bob KW4CQ

The waterfall display appears to show a lot of good information concerning the SSB signal I may be tuned to or those I see being displayed up or down the band.  Some signals appear to vary a lot in color and intensity.  Some sideband signals appear to have very sharp upper and lower occupied band edges while others appear to show audio peaks extending far beyond the filter bandwidth. Interpreting the displayed information properly seems a bit challenging.  I am just curious to know if anyone has done a write-up on this subject (with illustrations perhaps) they could share with the Flex user community?

John - AF3K

Bob, Great question.  While not specific to Flex you might want to take a look at this book (available on Kindle or Google books) "Software Defined Radio for Amateur radio operators and shortwave listeners" by Andrew Barron ZL3DW https://www.goodreads.com/book/show/33236364-software-defined-radio 

GL! John, AF3K

Wayne

Just quickly on the screen you can zoom in on the signal and visually see on ssb for example how wide it is on khz and in even more detailed zoom you can see the actual audio frequency response from lo frqs to high freqs detailing how the persons equalization affects the audio transmitted too much low or too little high or lack of width filtering etc. All in realtime.

Bob KW4CQ

Thanks, John. I’ll pick up a copy. Bob

Bill -VA3WTB

This is one of the best question I have seen in some time.

I have discovered the waterfall is not such a good tool to determine if a station is transmitting outside the band pass. Any signal stronger then s9 will start to show out past the band pass. As the signals are higher, perhaps s10 we see much more. But this does not mean that station is transmitting dirty.

Let me explain. Most radios have an IMD of around 36 down. So if the their signal is s9 they look clean. But lets say their signal is s10 or 20 over and there IMD is still 36db down, we see a mess in their signal because we see things below 36db as the signal rises to s10 +

If a signal is s9 and is transmitting out past the band pass, good chance they are transmitting dirty.

Keep in mind, that what we see on the Flex is also related to the display gain control slider.I set my slider to 27, this is a setting that works close to seeing an s9 signal. If I turn the slider to say 34 then even at s9 I can see things in a signal that should not be a problem but it looks like it is.

Martin AA6E

Waterfall colors are under your control. Adjust the display gain and color palette to your taste. Signals that don't have well defined edges in the spectrum are often distorted. Read up about intermodulation distortion. Often linears are overdriven so they're not as linear as they should be. 73 Martin AA6E

Bill -VA3WTB

That is correct, what I mean is that if we turn the gain to high, we see things that should not be visible. S9 is the sweet spot because that is a 36db IMD. What I do is tune to a known clean signal at s9 I adjust the gain slider to show clean skirts on the signal. Now any signal over s9 should show a distorted signal to me if they have an IMD of 36db

Dave S

[{"insert":"Very helpful as I was struggling with what appeared as distorted signals. Turns out it's the gain setting in my display... \n"}]

halmassey

The best use of the waterfall display is to increase your situational awareness of what is going on in and around the band. You can see ssb, cw, ft8, etc. You can find the weak dx signals really quickly and get your receiver tuned to them equally quickly. Using it for critical lab analysis of the signals seems like a mistake to me.