EUMETCast Dummy PLFrames.
I commented the other day about (possibly?) seeing more Dummy PLFrames being transmitted 'recently.'
Well, this is the case and I've received this explanation from Ops as to what they are:
Your observation is correct that there are more Dummy PLFrames recently due to filling some bandwidth that became free from decommissioned MetOp-A satellite data.
They are part of the DVB-S2 spec and are used for synchronisation and energy dispersal purposes when there is no "real" data to be transmitted in an already dedicated bandwidth.