"JC" wrote in message
. fr...
In a lossy coax the lost energy is, I suppose, heating up the dielectric.
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

Up to very high frequencies the major loss in coax is in wire. The skin
effect makes the center conductor effective wire diameter much smaller than
what it is at DC. The higher the frequency the more loss in the wire due to
the skin effect. The reason for some types of coax of the same diameter
have less loss is not because of the loss in the dielectric, but because it
lets the center conductor be a larger diameter for the same shield diameter.
Not much is lost in the dielectric. The other major loss is in the shield
and it is lost the same as in the center conductor.