[TowerTalk] SWR is what SWR meter measures

[Tom Rauch]

> I don't understand what is meant by "losses can actually
decrease when
> the mismatch is in a direction that decreases current"?

Losses are not evenly distributed between dielectric losses
and conductor losses at HF. As a matter of fact dielectric
losses are very small, almost all of the loss relates to I^2
R losses in the conductors.

That means if a mismatch results in line currents being
reduced over the length of the line, losses will commonly
decrease.

Transmission lines don't follow simple equations for
increased loss unless they are long compared to 1/4 wl.
Another way to look at this is without someplace for the
standing waves to stand you can forget using SWR ratio to
determine loss. Simple methods of determining loss using SWR
and matched loss won't be accurate.

It follows that open wire line isn't necessarily lower loss
than coax under conditions of high SWR with increased
current when the line is short, unless the open wire has the
same or less conductor resistance than the coax.

My only purpose in pointing this out is to show cases exist
where increased SWR actually results in reduced transmission
line loss. It's an important example showing limits of SWR
models like "mismatch loss", which are often taken far too
literally (even by skilled engineers).

73 Tom