[Skimmertalk] What causes audio images with QS1Rs?

[Bob Wilson, N6TV]

On Sat, Feb 23, 2013 at 1:30 PM, Pete Smith N4ZR <n4zr at contesting.com>wrote:

> During the ARRL CW contest, we had two Skimmers using the QS1R/Skimmer
> Server combination that each produced many false spots, with the
> "signature" commonly associated with Skimmers using simple SDRs,


I hope my QS1R wasn't one of them.  Noticing the same thing happening
before the contest, 10m only, with 192 kHz bandwidth, I went ahead and
edited my SkimSrv.ini file (used for "Contest rotation") to force it to
ignore all signals 130 kHz or more above the band edge.

Original:

CwSegments=1800000-2000000,3500000-3600000,7000000-7125000,10100000-10130000,14000000-14150000,18068000-18095000,21000000-21200000,24890000-24920000,28000000-28300000,50000000-50200000

Modified:

CwSegments=1800000-1900000,3500000-3600000,7000000-7125000,10100000-10130000,14000000-14130000,18068000-18095000,21000000-21130000,24890000-24920000,28000000-28130000,50000000-50200000

Here are some numbers that could reveal a new problem in CW Skimmer and/or
SkimSrv being introduced in the last year, that lead to more false image
signals being reported, though the evidence may not be 100% conclusive:

Contest              RBN       RBN Spots    % of
                  10m Spots  >= 28100 kHz   Spots
---------------  ----------  ------------   -----
2012 ARRL DX CW      93,317        502      0.54%
2012 WPX CW         132,751        332      0.25%
2012 CQ WW CW       244,242      6,249      2.56%
2013 ARRL DX CW     178,404      2,644      1.48%

73,
Bob, N6TV