Thanks' for the data Jim I think you may have the reason for the miss printing of the 500/1 mode on 500 , selective fading, from previous 'trials it showed to be very close in , even 50 Hz shift show
Dear Graham, LF Group, Well, not much to choose between the two here... see the output logs for both modes at the 2.5W level below. Some selective fading was evident, as you can see in the attachment