Strange Trace on Waterfall: Any Ideas?

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Joined: 2012/11/04 - 09:42
Strange Trace on Waterfall: Any Ideas?

I turned WSPR on this morning and it was fine for a while but (not very productive but I'm getting out and making the odd spot) then after a while I noticed the following on the trace:

Does anyone have an idea of what this could be? It seems to have gone away now, I live in a flat and the antenna is on the inside of the window so there are many opportunities for QRM - I'm just curious to see if anyone has seen this type of curved plot before.

Thanks in advance,
73 de M0TNC