"Antonio Vernucci" wrote in
:

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?

If you construct a cable of similar outside dimensions but using a foam
dielectric, it needs a larger diameter inner conductor. That accounts for
the lower loss at lower frequencies (typically below the GHz range.)


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?

See above.

If you use my calculator (link in earlier posting), it gives you the
coefficients of two terms of the loss model, one is due to I^2R and the
other V^2G. You can evaluate them at any given frequency and determine
the contribution that conductor and dielectric losses make at that
frequency for that cable type.

Does that help?

Owen


Thanks and 73

Tiony I0JX