In message , Jim Lux
writes
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.



Indeed. 'Low-loss' coax usually has less dielectric than 'high-loss'
coax (the less dielectric, the lower the loss).

However, it isn't the lack of dielectric which minimises the loss. It is
because, for a given outer diameter, in order to maintain the same
characteristic impedance, the diameter of the inner conductor has to be
made larger - so its resistance (and power loss) is less.
--
Ian