Useless info: My brother lives in Southend 
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Triple dip again today, although the second and third are very close.
Nothing odd in the Airspy graphs.
Just wondering, the message rate we all see is somewhat dependent on ground based radar systems interrogating plane ads-b systems. Perhaps one or more interrogators were taken off-line for some maintenance or some other reason. It could account for a drop. Am I wrong about the interrogation by radar systems?
Простите, я не знаю как правильно задать вопрос.
мне интересно почему самолет перед посадкой делает петлю? и что значит если он делает 2 или 3 петли?
с уважением Костя.
your question is anwered in the other topic 
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… and here we go again, spotted because I’m keeping an eye on the stats at the moment. Huge dip, very noticeable,
Me:
Yeah it’s odd. It looks like DF17 messages are down as well as others so whatever the cause it doesn’t seem to be related to ground interrogations.
Perhaps there some interference having an effect. It would be interesting to get a spectrum capture while it’s happening to see if there is anything obvious.
I have a similar dip every day between 04:00 and 09:00. IMO it is simply a lack of traffic during those hours.
@keithma I see from your signal strength graph (not posted above) that the minimum signal increased at the same time as the dip so it looks like it might be interference.
Interestingly I didn’t see a dip here (nr. Portsmouth). On a number of previous occasions I have seen a dip too but not as pronounced as you guys further east. Maybe conditions meant I didn’t hear the noise this time whereas I did previously.