In reasonably well constructed coax cables, the main source of loss up
to about 1GHz is the I^2R loss in the centre conductor. The inside of the
shield carries an equal (and opposite) current, but the current density is
lower so the I^2R loss there is less important. Dielectric loss is usually
less important still.

Ian and others,

thanks for your clear explanation, but I still have a doubt that you may kindly
clarify.

The 300-ohm TV flat ribbon specifications show an attenuation generally lower
than that of plain RG-8, despite the conductors of the ribbon are by far thinner
than those of RG-8 (especially than the cable shield).

What am I missing now?

Thanks & 73

Tony I0JX