Antonio Vernucci wrote:
For instance RG-213 is rated at 8.5dB loss for 100 meters at 144 MHz,
while RG-213 foam at only 4.5 dB. If G is relatively unimportant with
regard to loss, how can one explain that a change of insulation material
yields such a tremendous change in loss?

Those statements about most loss being due to I^2*R
losses are at *HF* frequencies. 144 MHz is NOT HF.
The difference in RG-213 and RG-213 foam is only 0.2
dB at 10 MHz while the difference between RG-58 and
RG-213 is about 0.7 dB at 10 MHz.
--
73, Cecil http://www.w5dxp.com
"According to the general theory of relativity,
space without ether is unthinkable." Albert Einstein