So with Ley's help I've removed the control head, stripped and checked that (we had previous issues with a sub-standard repair), then removed the transceiver and double checked all the connections.
No obvious issues found so far. Tomorrow, when the swell abates a little, I'll move into the back of the boat and check the antenna tuner and it's connections.
Crystal Blues is more than half way to St. Helena now, with (just) 825 nautical miles to run. Sea conditions have grown big again, with an objectionable 2.5 meter quartering swell hitting us on a 7 second period. This makes movement, day to day activity and even sleeping a little strenuous and tiresome. Ley is continuing to produce gourmet food, so we're eating very well. However we are definitely looking forward to some tropical sunshine and warm weather - four days of grey sky's and rainy conditions have taken the shine of the south Atlantic !
The shine has also been missing from our solar panels - on this north westerly course, with the winter sun already well to the north of the equator, our sails are blocking the sunshine even when the clouds are not. So we're getting very little energy from the solar system, and the Northern Lights generator is doing extra duty.