[Skimmertalk] [RBN-OPS] Spot fidelity

Pete Smith N4ZR n4zr at contesting.com
Tue Jan 17 05:32:20 PST 2012

Interesting report, Paul.  A few semi-thought-out reactions...

I'm not sure what to make of different Eu stations busting the same call 
at exactly the same time in the same way - perhaps QRN or something 
propagated by radio has interfered, because the CW Skimmer decoder is 
operating on a very short time interval before it moves on to the next 
stream.  I had wondered myself about whether a low SNR might be 
implicated, but the evidence so far is inconclusive.  Two stations 
operating the same validation level, and both hearing the same bust, 
could very well both decide to send the same busted spot to the RBN at 
the same time.

 From the RBN's perspective, it would make little difference if all EU 
Skimmers were running Aggressive validation, because with so many 
contributors in that area we are virtually certain of getting the spot 
from several.  The only real downside is that posting at all will occur 
a little further along in the station's efforts to attract callers, 
something that may not make much difference, since the RBN is typically 
minutes, not seconds, ahead of traditional spots.  However, I well 
understand that people like to get as many spots as possible, hence the 
appeal of running Normal rather than Aggressive.

For RBN users, the problem is a little different.  Some big multi-ops 
have reported that on the second afternoon of a major contest they were 
seeing as many as 80 percent bad spots.  At first, I thought, "How can 
this be?", because the error rate of all Skimmers, in the aggregate, is 
under 1.5 percent.  Then it dawned on me -  if RW9AS is calling CQ, and 
being spotted, and then a single Skimmer busts his call as (for example) 
RW9ASE, both spots will appear on the RBN, with seemingly equal 
validity, and if the multi-op has already worked RW9AS, its operator 
will see only the bad spot as potentially workable.  Not good, clearly.

For the moment, the best solution to this for users may be to connect to 
the RBN's ARCluster server and apply the Uniques>x filter.  What that 
does is to look at spots coming in and only pass them to the user if 
more than x Skimmers world-wide report the same call at the same time 
and frequency.  Combined with a spotterstate= filter, to try to make 
sure that you'll be able to hear what is being spotted, this should do a 
pretty good job of filtering out even double busts.

Meanwhile, we are also working on algorithms that might be used to try 
to catch this situation at the server as each new spot comes in, by 
comparing it to spots received on about the same frequency and figuring 
out who the outliers (probably busted) are.  This is not an easy chore, 
because the server saw *average* rates of 20 spots per second during 
CQWW 2011, but we're hopeful.  If anyone with programming skills that 
might be relevant is interested in becoming involved, by all means 
please let me know.

As a final aside, let me pass on my congratulations to the Skimmer ops 
worldwide - virtually all of you are reporting frequencies within +/- 
0.1 KHz of each other and of our standard frequency references.  That is 
a great help in our effort to put out the best quality spots possible.

73, Pete N4ZR

The World Contest Station Database, updated daily at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000

On 1/17/2012 6:26 AM, Paul_group wrote:
> before I start, apologies but this is very long winded.
> I recently had a fairly nasty e-mail exchange with a F6*** stn who
> demanded that I immediately close down my skimmer as I was deliberately
> misleading stations and that 75% of my spots were busted.  It turned out
> that he was particularly miffed as I'd spotted (U)T5G on 15m - as
> diplomatic relations have now permanently broken down with the pleasant
> gentleman from France I thought I'd better investigate anyway.
> G4HSO seems to run a very similar setup to mine and within reason our
> spots and SNR agree almost perfectly. I've put an example below. Where
> a busted call happens. Sometimes I bust the call, sometimes 'HSO skimmer
> busts the call but always we both either drop or insert a rogue
> character on the front of the call.
> I though I'd found an example where only I had bust a call at a good SNR
> but now I'm not sure. The example below with W9AS or RW9AS:  we both
> decoded W9AS but shortly afterwards on the same frequency I spot RW9AS.
>    A quick QRZ shows W9AS is a valid call where RW9AS isn't there.
> The thing is at the same time as me an almost equal split of skimmers
> around the world seemed to spot RW9 or W9  on the same QRG. Maybe I
> suspect this is down to an equal split of aggressive / normal
> validation? In addition, "R W9AS" is similar to "RW9AS". Maybe not to
> get too hung up on this particular example as its not a unique
> occurrence. The (U)T5G is another, I also saw (R)W1** spotted as W1** on
> top band recently. Again a mixture of skimmers spotting the two calls.
> I ran some tests using different validation and whilst aggressive does
> seem to be the way forward virtually none of the spots are then of any
> use to users as they are *always* post a none aggressive skimmer and it
> really does miss a lot of genuine good high SNR spots with well sent CW.
> Whilst this is a bit of speculation as to whether this links to call
> validation but with a dense population of skimmers in Eu I suggest
> running aggressive validation is actually a waste of electricity unless
> everyone does it.
> Going back to the initial complaint of 75% of spots being busted, if
> users suppress duplicate spots (why wouldn't they) and your running
> aggressive validation the users are only going to see your busted calls
> or the very occasional genuine new one.. is this a losing battle ;-)
> The second issue is spotting the same station on for example 3505.1Khz
> and 7010.2Khz - initially I had thought that the stn genuinely could
> have a readable 2n'd harmonic but the SNR in all cases I've found is
> identical. Maybe there was something in the QS1R hardware or active
> antenna none linearity but I cannot reproduce it on the bench or with
> locally generated test calls, I see other skimmers throughout the world
> doing this from time to time.
> In summary it would be nice to understand the best skimmer settings and
> if there are real decode quality issues to address how do we track them?
> As before, again I'm sorry this is long winded and I know its been
> discussed before ..... but after the nasty exchange experienced here
> maybe its worth revisiting?
> RW9AS example quoted above:
> DX de GW8IZR-#:14012.8  EW8MK        19 dB  25 WPM  CQ
> DX de G4HSO-#: 14012.8  EW8MK        20 dB  24 WPM  CQ
> DX de GW8IZR-#: 7001.7  SM5COP       31 dB  25 WPM  CQ
> DX de G4HSO-#:  7001.7  SM5COP       30 dB  24 WPM  CQ
> DX de GW8IZR-#:14019.5  HA6OD        09 dB  23 WPM  CQ
> DX de GW8IZR-# 18077.1  RX3AP        20 dB  24 WPM  CQ
> DX de GW8IZR-#:14025.3  OH2KI        35 dB  26 WPM  CQ
> DX de G4HSO-#: 14025.3  OH2KI        36 dB  26 WPM  CQ
> DX de GW8IZR-#:10117.0  DK8OV        23 dB  27 WPM  CQ
> DX de G4HSO-#: 10117.0  DK8OV        18 dB  27 WPM  CQ
> DX de GW8IZR-#:21017.0  UR5LGJ       11 dB  32 WPM  CQ
> DX de GW8IZR-#:10103.0  DK4AN        37 dB  24 WPM  CQ
> DX de G4HSO-#: 14021.0  TA1FA        15 dB  21 WPM  CQ
> *
> DX de G4HSO-#: 14014.0  W9AS         23 dB  25 WPM  CQ
> DX de GW8IZR-#:14014.0  W9AS         17 dB  25 WPM  CQ
> *
> DX de GW8IZR-#:14003.0  DJ2BC        32 dB  25 WPM  CQ
> DX de G4HSO-#: 14003.0  DJ2BC        15 dB  25 WPM  CQ
> DX de G4HSO-#:  7016.0  F6FLF        12 dB  26 WPM  CQ
> DX de GW8IZR-#:14028.7  DL9LM        37 dB  29 WPM  CQ
> *
> DX de GW8IZR-#:14014.0  RW9AS        18 dB  25 WPM  CQ
> *
> DX de GW8IZR-#:14046.8  OK2PRQ       10 dB  24 WPM  CQ
> DX de G4HSO-#:  7010.0  F9EW         26 dB  17 WPM  CQ
> DX de GW8IZR-#: 7010.1  F9EW         28 dB  20 WPM  CQ
> DX de GW8IZR-#:18069.0  UR3UI        11 dB  26 WPM  CQ
> DX de G4HSO-#: 18069.0  UR3UI        16 dB  26 WPM  CQ
> DX de GW8IZR-#:21026.0  R3QA         13 dB  32 WPM  CQ
> DX de G4HSO-#: 21026.0  R3QA         25 dB  33 WPM  CQ
> And from RBN a SH/DX RW9AS
>    14006.8  RW9AS       17-Jan-2012 1101Z  18 dB  23 WPM  CQ
> <TF3Y>
>    14006.7  RW9AS       17-Jan-2012 1100Z  21 dB  23 WPM  CQ
> <SK3W>
>    14006.8  RW9AS       17-Jan-2012 1100Z  15 dB  23 WPM  CQ
> <IK3STG>
>    14006.8  RW9AS       17-Jan-2012 1058Z  13 dB  23 WPM  CQ
> <HA6PX>
>    14006.8  RW9AS       17-Jan-2012 1058Z  12 dB  23 WPM  CQ
> <DK9IP>
>    14006.8  RW9AS       17-Jan-2012 1058Z  20 dB  24 WPM  CQ
> <G4HSO>
>    14006.7  RW9AS       17-Jan-2012 1058Z  26 dB  24 WPM  CQ
> <DL8LAS>
>    14006.8  RW9AS       17-Jan-2012 1058Z  21 dB  23 WPM  CQ
> <PA1T>
>    14006.8  RW9AS       17-Jan-2012 1058Z  23 dB  24 WPM  CQ
> <GW8IZR>
>    14006.8  RW9AS       17-Jan-2012 1058Z  32 dB  24 WPM  CQ
> <RZ3DVP>
> followed by sh/dx W9AS
>    14006.8  W9AS        17-Jan-2012 1057Z  24 dB  23 WPM  CQ
> <OL5Q>
>    14006.9  W9AS        17-Jan-2012 1051Z  08 dB  23 WPM  CQ
> <RU9CZD>
>    14014.0  W9AS        17-Jan-2012 1013Z  13 dB  24 WPM  CQ
> <IK3STG>
>    14014.0  W9AS        17-Jan-2012 1013Z  38 dB  24 WPM  CQ
> <OH6BG>
>    14014.0  W9AS        17-Jan-2012 1013Z  16 dB  24 WPM  CQ
> <SK3W>
>    14014.1  W9AS        17-Jan-2012 1012Z  27 dB  23 WPM  CQ
> <US0KW>
>    14014.0  W9AS        17-Jan-2012 1012Z  24 dB  24 WPM  CQ
> <DL8LAS>
>    14014.0  W9AS        17-Jan-2012 1012Z  23 dB  24 WPM  CQ
> <OL5Q>
>    14014.0  W9AS        17-Jan-2012 1011Z  14 dB  23 WPM  CQ
> <HA6PX>
>    14014.0  W9AS        17-Jan-2012 1002Z  17 dB  25 WPM  CQ
> <GW8IZR>

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