[Skimmertalk] Duplicate Spots

Mon Jan 27 18:55:29 EST 2025

Many thanks Bob.

I was not aware of that tool.  Looks very interesting and definitely 
beats how I've been doing it manually.

73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com

On 1/27/2025 5:40 PM, Bob Wilson, N6TV wrote:
> Without getting into the weeds, the main thing to avoid is reports 
> from the same skimmer location using the same RBN callsign but with 
> two totally different Rx antennas covering the same frequencies, so 
> spots only a few minutes apart, or within the same minute, from the 
> same skimmer, with the same frequency, show two completely different 
> signal reports.
>
> Each individual SNR report by each Skimmer is very accurately 
> calculated by the SkimSrv software.  Though they may vary a lot over 
> time, the MEDIAN of all reports is usually very stable.  But 
> calculating a median report when each duplicate report skews too much 
> because of totally different antennas leads to meaningless statistics 
> since it's like reports from two completely different skimmer 
> locations even though they are at the same location.
>
> What you want to avoid it seeing reports like this from the Spots 
> Analysis Tool caused by duplicate posts (graphic may be deleted by 
> this reflector, but see the archives for the attachment.
>
> image.png
>
> 73,
> Bob, N6TV
>
>
> On Mon, Jan 27, 2025 at 3:04 PM Jeff Blaine <KeepWalking188 at ac0c.com> 
> wrote:
>
>     Bob,
>
>     In the context of multiple antennas & skimmers, I'm curious about
>     this data analysis use with skimmers.
>
>     Maybe it's been discussed before, but the RBN reports of the same
>     station from the same skimmer vary quite a lot over time in my
>     observation.  I've noticed this in many contests where I may have
>     two screens of the RBN website feed up - one looking at my signal
>     and another looking at another guy who I'm interested in comparing
>     too, to see how we look at a single given skimmer site.  In this
>     case, these reports can vary by 10+ db very easily, especially on
>     the lower bands.
>
>     Why I'm thinking about that flows from your comment on the data
>     analysis and it reminds me that I have seen some guys talking on
>     the reflectors about using RBN reports for fine tuning antennas
>     where they are considering changes that are in the few-dB range
>     and using RBN as the measurement method.  I don't understand how
>     that can be done with precision given the variability the
>     atmosphere provides in cases excluding ground wave prop.  It seems
>     like the noise in the data would swamp the relative compare value
>     for this objective.
>
>     Skimmer reports SNR so both the noise floor skimmer sees as well
>     as the signal(s) of interest needs to be stable over time so that
>     Skimmer is able to provide a repeatable report (at least within a
>     short measurement window). Otherwise it seems like a guy would
>     need to have two very different antennas (for example one skimmer
>     tied to his TX vertical and another one tied to a low-noise
>     directional RX) so that the SNR difference would be significant
>     enough to overcome the prop.
>
>     Maybe there is a statistical method that addresses this? Or maybe
>     I'm missing a key point here that is otherwise obvious?
>
>     73/jeff/ac0c
>     alpha-charlie-zero-charlie
>     www.ac0c.com <http://www.ac0c.com>
>
>     On 1/27/2025 1:21 PM, Bob Wilson, N6TV wrote:
>>     If you have two skimmer instances monitoring the same
>>     frequencies, they should never post under the same Skimmer
>>     callsign, otherwise the reports will be quite useless for
>>     data analysis, because the signal reports will be bouncing all
>>     over the place and you can't tell which report to use. 
>>     Eliminating dupes alone doesn't solve this problem, because the
>>     same station could be reporting with two different signal
>>     strengths every few minutes, depending on which skimmer heard it
>>     first.
>>
>>     If the two SDRs or two Skimmers are monitoring the same band
>>     segments, use 3V8SS-1 for one and 3V8SS-2 for the other.  You
>>     need to run two independent copies of Aggregator to make this
>>     work right, since the posted callsign is determined by the first
>>     SkimSrv.ini, not by Aggregator.
>>
>>     For more details explaining how to do this, please review this
>>     post by Aggregator author W3OA:
>>
>>     https://groups.io/g/RBN-OPS/message/4938
>>
>>     73,
>>     Bob, N6TV
>>
>>
>>     On Sun, Jan 26, 2025 at 6:12 AM Ashraf Chaabane
>>     <ash.kf5eyy at gmail.com> wrote:
>>
>>         Hi All,
>>
>>         I use two receivers with separate receiving antennas. Both
>>         are skimming
>>         to Aggregator. How can I ensure Aggregator doesn't send the
>>         same spot
>>         twice if it happens that they come from both receivers?
>>
>>         73 Ash 3V8SS
>>
>>
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