[RTTY] Skimmer spots dropped at VE7CC cluster node

Mon Oct 5 10:38:28 EDT 2015

Hi Jim,

Your callsign was spotted 273 times on the first day of the contest. It also appeared 41 time on the VE7CC list of the dropped 
spots, but this does not necessarily mean that your call was busted. This just means that another callsign, similar to yours, 
was copied on a frequency close to yours. In 18 cases it was W7DRM, and in another 18 cases it was W7RN. Both callsigns belong 
to the active contesters. Decoding errors are random, it is extremely unlikely that 18 spotters made exactly the same error.

In the remaining 5 cases, the callsigns were W7CY, W7RYY and DW7GY, which seem to be the busts. Therefore, the error rate for 
your callsign was 5/273 = 1.8%.

73 Alex VE3NEA

On 2015-10-05 08:38, Jim W7RY wrote:
> I disagree Pete.
> My call was never spotted by any skimmer. But it was "incorrectly" spotted 41 times.
>
> Sounds like 100% failure to me.
>
> 73
> Jim W7RY
>
>
>
> -----Original Message----- From: Pete Smith N4ZR
> Sent: Monday, October 05, 2015 4:57 AM
> To: Jim W7RY ; RTTY Contesting
> Subject: Re: [RTTY] Skimmer spots dropped at VE7CC cluster node
>
> Jim, the numbers don't bear that out.  Typical busted calls rates with
> RTTY Skimmer are in the 1.4-1.7 percent range.  It would be nice to get
> them down into the same range as CW Skimmer (< 1 percent), but I can't
> imagine what the technical problems would be.  I am reasonably confident
> that  VE7CC has put his finger on one problem - RTTY signals tend to be
> much more closely "zero beat" (CQer and caller) than CW signals.  Also,
> there are many more possible Baudot characters than CW letters,
> increasing the risk of miscopies due to interference.
>
> Another thing that people seem to forget is what I call the "crowd
> effect."  If you have 50 Skimmers copying the same transmission at a
> given time, and each of them has a 1percent error rate, there's a 50
> percent chance that one of the Skimmers will miscopy.
>
> This is where tools like cluster-side filters come into play.  I believe
> that VE7CC and AR Cluster V6/CT1BOH both use similar mathematical
> techniques to sort out the busts from the correct copies. They do work.
>
> It might be interesting to know what the average Signal-to-Noise ratio
> was on the busted spots of your call. There are a large number of
> Skimmers in the eastern US and in Europe, and the "competition" may have
> been a lot louder than you in those "markets" when you were being busted
> a lot.
>
> 73, Pete N4ZR
> Download the new N1MM Logger+ at
> <http://N1MM.hamdocs.com>. Check
> out the Reverse Beacon Network at
> <http://reversebeacon.net>, now
> spotting RTTY activity worldwide.
> For spots, please use your favorite
> "retail" DX cluster.
>
> On 10/5/2015 7:08 AM, Jim W7RY wrote:
>> Probably not. Using FSK generated by DOOK (5 KHZ AFSK) and converted to FSK
>> from 2-Tone.
>> Icom IC7600
>>
>>
>> What it really looks like is the skimmer software has poor decode. If you look closely at the busted calls, the calls are very
>> similar. So more of poor decode than too close to someone. LOTS of busted calls are off by one letter.
>>
>> Am I calling your baby ugly?  If the shoe fits....
>>
>>
>>
>> Thanks
>> 73
>> Jim W7RY
>>
>>
>> -----Original Message----- From: Pete Smith N4ZR
>> Sent: Monday, October 05, 2015 3:36 AM
>> To: rtty at contesting.com
>> Subject: Re: [RTTY] Skimmer spots dropped at VE7CC cluster node
>>
>> Or conceivably because of less than perfect AFSK (bit jitteror
>> distortion from overdrive?)
>>
>> 73, Pete N4ZR
>> Download the new N1MM Logger+ at
>> <http://N1MM.hamdocs.com>. Check
>> out the Reverse Beacon Network at
>> <http://reversebeacon.net>, now
>> spotting RTTY activity worldwide.
>> For spots, please use your favorite
>> "retail" DX cluster.
>>
>> On 10/4/2015 9:18 PM, Lee Sawkins wrote:
>>> You get busted because you are too close in frequency and call to W7RN or
>>> W7DRM and they were there first.
>>>
>>> 73 Lee
>>>
>>> ----- Original Message -----
>>>
>>> From: "Jim W7RY" <w7ry at centurytel.net>
>>> To: "Lee Sawkins" <ve7cc at shaw.ca>, rtty at contesting.com
>>> Cc: dezrat at outlook.com
>>> Sent: Sunday, October 4, 2015 11:41:44 PM
>>> Subject: Re: [RTTY] Skimmer spots dropped at VE7CC cluster node
>>>
>>> So why am I in the busted list 41 times?
>>>
>>> 73
>>> Jim W7RY
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: Lee Sawkins
>>> Sent: Wednesday, September 30, 2015 6:19 PM
>>> To: rtty at contesting.com
>>> Cc: dezrat at outlook.com
>>> Subject: [RTTY] Skimmer spots dropped at VE7CC cluster node
>>>
>>> These links may be interesting to some of you. These are the typical
>>> rejected spots of any CC Cluster.
>>>
>>> RTTY skimmer spots are considered valid if spotted by ONE Skimmer. RTTY
>>> Skimmers are generally more accurate than CW and there are simply not
>>> enough
>>> of them to use 2 or more Skimmers to validate them. CW spots are valid if
>>> spotted by 2 or more Skimmers.
>>>
>>> Here is the list of dropped Skimmer spots by the VE7CC-1 cluster.
>>> If you connect to the RBN directly, you will receive all these spots as
>>> well
>>> as the good ones.
>>>
>>> Many times there are two calls in succession that are dropped for RTTY
>>> calls. I am receiving data from both the RBN and DL4RCK for redundancy.
>>> Usually they both spot the same RTTY calls.
>>>
>>> Most columns are self explanatory.
>>>
>>> The number directly before a skimmer call is a quality number. It is the
>>> number of times a call has been detected as correct minus the number of
>>> times it is busted. When the number decreases below 5, it is no longer
>>> considered valid. If the active call has not been spotted in 12 minutes it
>>> is also no longer considered valid. In one place, for 9A1A the quality
>>> number is over 2000. This means 9A1A has been spotted over 2000 times on
>>> the
>>> same frequency!
>>> "Sysop added" means I have manually added a call to the list because it is
>>> busted all the time and is never good.
>>>
>>> http://www.bcdxc.org/ve7cc/ccc/Busted-26-Sep-2015.txt
>>> http://www.bcdxc.org/ve7cc/ccc/Busted-27-Sep-2015.txt
>>>
>>> Lee
>>> _______________________________________________
>>> RTTY mailing list
>>> RTTY at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/rtty
>>>
>>>
>>> _______________________________________________
>>> RTTY mailing list
>>> RTTY at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/rtty
>>>
>>
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