JC wrote:
In a lossy coax the lost energy is, I suppose, heating up the dielectric.

At HF, the loss mostly in heating up the conductors from IR losses. You
need to get well up into UHF territory before dielectric losses start to
become significant.

To try to visualize that I stripped off 30 cm of dielectric from an old
RG58 cable and put it in a 900 W 2450 MHz standard microwave oven together
with a 100cc cup of water as dummy load.
2 minutes after switching on the water was boiling but the polyethylene was
only slightly warmer due to the proximity to the boiling water., Can I
conclude that RG58 dielectric has no loss at 2350 MHz ?
Certainly not ( it is well known that all the PE food containers used in
such ovens are not heated ), but what is wrong in this test ? how does it
differ from the dielectric heated in an actual operating lossy cable ?
JC