Receive spectrum #Waterfall #Elecraft


Arthur Bernstein
 
Edited



 

Begin forwarded message:

From: ARTHUR BERNSTEIN <n2ka@...>
Date: August 1, 2021 at 5:41:23 PM EDT
To: WSJTX@groups.io
Subject: FT8

This is a photo of my screen on 6 meters running a K3.
Wonder why there is evidence of intense signals at upper and lower parts of bandpass. BW of K3 is set to  4khz. Looks like noise above 2500 hz and below about 500 hz. Have worked stations in these areas.
Could this be nature of K3’s IF bandpass?
Art, N2KA




Reino Talarmo
 

Hi Art,

You spectrum is wider than your receiver bandwidth and Flatten is activated. The sharp noise drops outside passband results artifacts to the flattening function that is only as fifth degree fitting. Either make waterfall narrower especially set Start frequency 200 to 300 Hz range or untick Flatten.

73, Reino OH3mA


Alan G4ZFQ
 

Wonder why there is evidence of intense signals at upper and lower
parts of bandpass.
Art,

Because these are "signals".
Maybe real, more likely spurii from some electronic device.
Needs investigating, any sign of modulation? Through the antenna? Continuous? Drifting? Directional?

73 Alan G4ZFQ


Alan G4ZFQ
 

You spectrum is wider than your receiver bandwidth and Flatten is activated.
Reino,

I did not know this is a known artefact.
Yes, I see now, I'd never opened up the spectrum so far!

73 Alan G4ZFQ


Michael Black
 
Edited

That's because the "Flatten" option doesn't like to see the edges of the bandpass.
 
#1 Turn off "Flatten" and change your frequency to a quiet spot (like 5kHz below an FT8 band).
#2 Change the Spectral Display pulldown to "Current" instead of "Cumulative" -- you already have the "Current" display which is good for doing this.
#3 Adjust your bandwidth as wide as you can -- you should see the drop off changing on the low and high side of your rig change as you adjust bandwidth.  If you can widen your bandpass over 3000 do it now and if you can the drop off a bit below 200 is good.  Some rigs can't get much better than 2400Hz width.
#4 Adjust "Start 0 Hz" so that the low side is close to being a flat line (i.e. trim off the edge of the bandpass)
#5 Adjust the width of the waterfall with Bins/Pixel and the actual window adjust to trim off the high side of the bandpass close to a flat line.
#6 Turn "Flatten" back on and the waterfall will be what you want.
 
Here's an example where flatten will cause the effect your see 

Make the adjustments and you get this


 
Mike W9MDB
 
 
 
 

On Monday, August 2, 2021, 01:45:05 AM CDT, Arthur Bernstein via groups.io <n2ka@...> wrote:
 
 
That's because the "Flatten" option doesn't like to see the edges of your bandpass.
 


 

Begin forwarded message:

From: ARTHUR BERNSTEIN <n2ka@...>
Date: August 1, 2021 at 5:41:23 PM EDT
To: WSJTX@groups.io
Subject: FT8

This is a photo of my screen on 6 meters running a K3.
Wonder why there is evidence of intense signals at upper and lower parts of bandpass. BW of K3 is set to  4khz. Looks like noise above 2500 hz and below about 500 hz. Have worked stations in these areas.
Could this be nature of K3’s IF bandpass?
Art, N2KA