Dave Sergeant wrote:

At first I thought much of this loss was due to the series loss resistance
of the matching capacitors (Philips 376) but further calculations from the
datasheets shows this not to be the case, as this is only around 50
milliohms.  What I need is an accurate formula for calculating the skin
effect resistance of the wire.  The 98 ARRL handbook has a 'rough guide'
formula which would increase the resistance by a factor of around 3.5,
which is not enough, unless there is another effect I have overlooked.

I understand from measurements made by Andrew ZL2BBJ, who uses a
transmitting loop, that the effective resistance of the wire is
increased not only by skin effect, but also by induction losses into
lossy ground.  The "eddy currents" in the ground reflect a small
resistance into the loop impedance.  Even a "big diameter tube" for a
loop antenna can not avoid the induced ground losses (at practical
heights above ground).

Bob ZL2CA