Panadapter hump
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Posted Wednesday, April 18, 2007 9:05 PM
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Remarkable difference between Power SDR and recent SDR-X panadapter displays with respect to the "hump" that can be seen on the panadapter display about -11Khz from VFO setting.

PowerSDR:

SDR-X:

Way to go! "Hump" is all but gone on the new alpha software.

Post #261
Posted Friday, April 20, 2007 3:56 AM
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Hi Craig,

Good work. As I am presenting the SDR-1000 used as clubstation to a bunch of operators,
I always hear the question: What is that "hill" down there.

The example that you are presenting has obviously a quite bad ground loop with more the 20 dB
difference min to max. Our SDR-1000 -11kHz "hill" is not as bad as yours, but it is also existent.

The question that want to ask: Do you simply flatten the hill on the panorama display side or is
a software improvement atacking the causation ?

To explanain my question: If you have an SSB signal at lets say - 20kHz distance to your selected
actual frequency and start to push the background of the panorama to get that SSB Signal inside
your filter. What happens with that SSB signal as it passes the area of - 11 kHz. Will it dissapear and
and then grow again to its former size as it aproaches your filter ? Or will it stay all the time in its
real altitude of lets say for example -70 dBm ?

73 de DK9NW Bernhard
Post #262
Posted Saturday, April 21, 2007 9:25 PM
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Bernhard,

I must admit that the image of the panadapter that I showed with the large hump is the worst case. Most of the time, I see only a narrow "hill" that is 20-30 dBm above the noise. It does not impact on receiver performance. It looks like a signal on the panadapter display. One can track another signal through this "hump", as you suggested. However, this is hard to do because the hump jumps 3kHz when the DDS frequency changes. To answer your question: I believe that I can see the signal superimposed on the panadapter hump without a change in perceived amplitude on the display. That is, a -70 dBm signal remains -70dBm when it is superimposed on the hump. I will make some additional observations on this to verify this.

Finally, I want to point out that the severe looking hump that I posted occurs at high frequencies, and high pre-amp settings, and can swamp my sound card causing a thumping sound even though it is 11 KHz away. The new branch of software has removed this severe hump.

I point this out to illustrate that at least some of the hump for some users may NOT be due only to ground loops, but to a peculiar effect of the software processing that has been corrected by a recent change in the new branch (SDR-X). My guess is that it may have something to do with Bob's (N4HY) moving the DSP oscillator after the DDS and HW Filters in SVN 1143. (But this is only speculation on my part).

I hope this helps or is of some use to you.

73

Craig

KC2LFI

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