As said in the previous post, these signals could also belong to a Narrowband (Under 500 kHz) Power Line Communications (NB-PLC) system. Just to investigate this second hypothesis, my friend Bjarne conducted a series of interesting measurements directly on the site since he's the owner of the Kongsfjord KiwiSDR. Below in Fig. 1 the map with time and locations of the measurements (blue squares) and the power grid layout (Kongsfjord transformation station is indicated with the red square).
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| Fig.1 - Power Grid layout and location of measurements |
Quoting the eamil sent me by Bjarne "Last weekend I did some noise measurements on different locations nearby my QTH: one very close to the transformation station in Kongsfjord, and one furthest away 25 km by road. Receiver was RSP1A at 1536 kHz sampling, connected to a Microsoft Surface Pro3 running on battery. The antenna was a Wellbrook loop, powered from an external battery. So everything was off-grid. I did note some interesting variations below 500 kHz as I rotated the loop. The wav file 20180818_110154Z shows a recording taken 100 meters from the transformation station: first, pointing at the station, then rotated for maximum null.".
RF wav files were recorded in HDSDR, so I used that program for playback as well. Figure 2 is related to the playback of the file recorded close to the transformation station (20180818_110154Z) and shows the moment of the antenna rotation:
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| Fig. 2 - 20180818_110154Z recording |
Figure 3 shows the same test performed at the second location (20180818_104203Z):
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| Fig. 3 - 20180818_104203Z recording |
We are beginning to think that the signal may be associated with power lines after all? I think we'll end up asking for a clarification from the power company, that's the better choice.
By the way, while in July we could see up to four signals, since 16 August we see only twos (#3 and #4 consisting of single tones)
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| Fig- 4 |
(to be continued)
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