Antonio Vernucci wrote:
since most of the loss in practical coax cables is due to I^2R loss
(compared to V^2G)

A quick question. If most of the the cable loss is due to I^2R, how can
one explain that the foam versions of common coaxial cables show a much
lower loss than versions having solid PE insulation?

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?

Thanks and 73

Tiony I0JX

144 MHz isn't HF, which is where the original statement is valid. At
frequencies above around 50 MHz, depending on the dielectric, the
dielectric loss starts to be more significant.

Another trap for the unwary, when comparing coax losses, has to do with
skin effect and the thickness of the copper or silver cladding on the
center conductor. You could have an air insulated coax with silver
plated over stainless steel where the loss is actually greater at low
frequencies than higher, because the skin depth is greater at low
frequencies and the current is flowing mostly in the SS, rather than the
copper. (such coax is used in cryogenic applications, lest one think
it's overly contrived as an example)