Apologies to any chasers waiting for me to appear on frequency as alerted and self spotted. Light eventually dawned when I failed to be heard when responding to CQ calls; no modulation. Tests have just revealed a defective microphone extension cable.
This also explains why people were so inconsiderate as to steal my frequency at least three times when there was plenty of space on the band for once.
As the next serious series of activations is planned for the Isle of Man I am very pleased to have discovered the fault today.