Hi Clive,
That's a PAW ATOM-GRID Ground Station (PWGROVEFM). After several years of trying, we have finally persuaded SkyDemon to show the Ground Stations as Masts instead of aircraft! They only show with the latest PAW and SD software versions, and for anyone else reading this, you also need to enable 'Display Ground Stations' on the PAW Configure Screen.
Next bit edited to correct a mistake in my understanding, sorry for any confusion this may have caused:
On Sky Demon the Ground Station Masts periodically change colour between Green, Yellow and Red. I had presumed it reported signal level, but it turns out that was incorrect (it does happen occasionally - I’m only human.) Thankfully Lee has now advised me that the colour change
DOES NOT indicate signal strength, but - apparently - reflects the time since SkyDemon last received a
position report from that particular Ground Station. This is however complicated by the fact that ATOM Ground Stations are designed to optimise uplink of traffic over transmission of their own position, - so when traffic density is high and the uplink is busy, the station automatically reduces the frequency of its position reports, so the mast will change colour to Yellow or Red -
even though there is no degradation in signal.
The important thing is that if you can see a Ground Station Mast on screen (of whatever colour), you will be able to receive uplinked Flarm traffic positions, Mode-S MLAT positions instead of bearingless warning rings (subject to there being sufficient PAW or 360Radar ground station coverage to achieve multilateration and Mode-S/3D being enabled on the PAW Configure Screen) and Metars (providing you are near the station long enough for the Metars to upload).
Hope this is now much clearer.
Best Regards
Peter