Locked Re: Water Fall display distribution of users #Waterfall #TechnicalHelpQuestion

Mike Black

You don't say what rig you have but you're correct many rigs have about a 2400Hz bandwidth.
If you turn off Flatten, set Start=0, and increase Bins/Pixel to see the right edge, and go to a quiet spot (usually 5Khz below or above the FT8 segment) you can see your Rx bandwidth which should look something like this.  Your edges are probably not as steep as my SDR.
Inline image

#1 Waterfall is not limited to 2.5KHz -- what makes you think it is?  The rig bandwidth is the main limiting factor,.
#2 Where do see a recommendation to limit to 1500-2000?  There is mention that is what the split modes do.   A couple of us have been on the war path the last few years to clean up all the operators generating harmonics.  None of them were using split mode as that mode avoids even the 2nd harmonic which could be at a minimum of 3KHz (i.e. 1.5Khz*2=3KHz).  We're down to seeing about 1 or 2 ops generating harmonics per week now.
#3 If you use Rig Split or Fake It any harmonics you generate are unlikely to be seen.  Better to not generate any as that is some of your power being wasted.
#4 You can't see your own harmonics without another receiver.
#5 Yes -- transmitting above 2400 or so will limit who sees you.  I've worked with many operators with 2KHz or less bandwidth as they didn't understand the effect on decoding.

Mike W9MDB

On Wednesday, October 6, 2021, 04:16:59 PM CDT, Chuck Moore via groups.io <wd4hxg@...> wrote:

While trying to identify an anomaly around 2300 Hz on the waterfall display I was curious about what is above
2500 Hz. The typical grab the edge of the waterfall display with the mouse and pull right did nothing of course.
But after a bit of lifting various rocks I found the control to set the lower edge frequency of the waterfall. As my
rig will allow a 4 KHz wide IF bandwidth I decided to see what was above 2500 Hz and set the lower edge of the
waterfall to 1000 Hz which pushed the upper edge of the water fall to 3500 Hz.  After a few minutes the display
shown below, revealed a number of signals above the default 2500 Hz limit. This was observed while operating
on 17 Meters (18.100 MHz USB).


A couple of questions come to mind. (this is not a request for software changes but just a query.)

  • Why is the waterfall limited to an  absolute bandwidth of 2500 Hz?
  • In reading the manual, the recommendation is to only use the 1500 Hz to 2000 Hz audio
    range for transmission to mitigate transmission of audio harmonics. Of course if I open
    my IF Bandwidth to 4 KHz I have just negated the reason for using the specified frequency
    segment. How much of a problem are audio harmonics?
  • Is the audio harmonic content a show stopper if the 1500 Hz to 2000 Hz rule is ignored?
  • Can the waterfall be used to gauge the effects of audio harmonics?
  • It was a bit of a surprise to see the gap from 2300Hz to about 2550 Hz. But more puzzling
    to me was the cluster of ops from about 2550 Hz to 3000 Hz. Would their operation there
    not limit the number of distant ops that can decode the ops operating above 2550 Hz?
    Why stop at 3000 Hz?


Chuck WD4HXG

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