[Skimmertalk] Duplicate Spots

[Bob Wilson, N6TV]

Here's the direct link to the RBN Spots Analysis tool:

https://reversebeacon.net/analysis/

73,
Bob, N6TV


On Mon, Jan 27, 2025 at 3:55 PM Jeff Blaine <KeepWalking188 at ac0c.com> wrote:

> 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-charliewww.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: 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-charliewww.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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>>
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