"Antonio Vernucci" wrote in
:

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).

Under matched line conditions, the 300 ohm line transfers the power at
higher voltage and lower current, one sixth of the current, so even though
the conductors might seem relatively thin (RF R is proportional to diameter
for wide spaced line), I^2R loss is lower.

Owen