I am modelling a Double Bazooka constructed of RG58C/U, and am interested
in a method of estimating the effective RF resistance of the outer of the
outer conductor compared to a round copper conductor of the same diameter.

The structure loss calculated by NEC-2 is about 2%, so it is a fairly small
quantity.

The model so far is of a Double Bazooka resonant at 3.6MHz at 10m height
over average ground, constructed entirely of Belden 8262 (RG58C/U), and fed
with 25m of the same line. The model ignores the effect of the jacket on
the radiator, and assumed that it is a round copper conductor of the same
diameter as the sheild of the coax. The draft results at at
http://www.vk1od.net/DoubleBazooka/Fig01.gif .

Owen