[CQ-Contest] Busted Reversed Beacon Network spots

Brett Graham vr2bg at harts.org.hk
Sat Jun 15 10:17:42 EDT 2013

Admission of a little over one-per-minute wrong-freq-same-band RBN spots 
prompted me to finish the queries I started working on back in 2011 to 
find all the bogus-frequency spots on RBN - a project I started when 
like HB9CVQ, somebody else noticed RBN spotting him somewhere he wasn't 
transmitting & unlike HB9CVQ, was worried he was transmitting a fecal 
signal as he didn't know if his transmitter was clean or not.

Fecal signals we have been told are one of the reasons for 
bogus-frequency spots on RBN.

DJ7WW subsequently mentioned ON5KQ's skimmer.  It, along with most of 
the other skimmers, were making bogus-frequency spots in the 2013-03-08 
RBN spot data I have been working with most recently:

81 skimmers spotted at least once the same call within one minute as 
another skimmer spotted that call - but on a frequency >1 kc away but 
still on the same band where the other skimmer spotted it.  That was 87% 
of all skimmers QRV that day.  Total of these wrong-freq-same-band 
spots: 5962.

69 skimmers spotted at least once the same call within one minute as 
another skimmer spotted that call - but on a different band.  That was 
74% of all skimmers QRV that day.  Total of these wrong-band spots: 885.

There were 175584 RBN spots that day - excluding DXpeditions & special 
event calls - stations potentially on >1 band or >1 frequency on the 
same band simultaneously.  Being a weekday, deliberately fecal signals 
from dodgy contesters should have been largely avoided.  The total of 
bogus-frequency spots were just shy of 3.9% of the total of the data set 
as described - nearly twice the high end of the range I had first 
suggested I thought it might be.

Who knows, maybe when diluted with the additional activity during a 
contest that rate does go down.  And/or maybe there is something to the 
chatter about skimmers not hearing so well stations during contests that 
they seem to hear the rest of the time.  Certainly not me, having 
previously been involved in developing, debugging & deploying SDRs & the 
pay-TV platforms they received long before skimmer appeared!

Anyway, on that day there were on average nearly five bogus-frequency 
RBN spots each minute.  The data has been there for anyone without 
confirmation bias to download & see for themselves.

The receiver performance reference mentioned below, as noted by DJ7WW, 
is irrelevant - though the product itself is an excellent example of 
another reason we keep being told is behind wrong-band-same-freq RBN 
spots - though most of those spots come from skimmers that are not using 
receivers of the type we have been told are the culprit.


> Interesting - I "admitted" what? That there are a lot of Softrock-type
> receivers on the RBN, some of which have inadequate I/Q image
> reduction? Sure. That direct downconversion receivers like the QS1R
> occasionally throw what look like I/Q spots, even though there is no
> simple explanation. Sure. I saw mine throw one of those just
> yesterday. Wish I knew why.
> The RBN teamis actively working on a promising technological solution to
> get rid of all of thisclass of busted spots.
> Wrong-band spots are quite another creature. I'm still waiting for data
> on these, but think that either inadequate harmonic suppression and/or
> intermod will be shown to be the source. If that's the case, then the
> receiver used probably makes little difference.
> Bret, before you attack SDR receiver performance indiscriminately, take
> a look at Rob Sherwood's review of the KX3.

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