"William E. Sabin" sabinw@mwci-news wrote in message ...
....

The usage of complex conjugate Z0* becomes
significant when calculating very large values of
VSWR, according to some authors. But for these
very large values of standing waves, the concept
of VSWR is a useless numbers game anyway. For
values of VSWR less that 10:1 the complex Z0 is
plenty good enough for good quality coax.

My working definition for SWR is (1+|rho|)/|(1-|rho|)|. (Note the
overall absolute value in the denominator, so it never goes negative.)
Rho, of course, is Vr/Vf = (Zload-Zo)/(Zload+Zo), no conjugates. In
that way, when |rho|=1, that is, when |Vr|=|Vf|, SWR becomes infinite.
When |rho|1, SWR comes back down, and corresponds _exactly_ to the
Vmax/Vmin you would observe _IF_ you could propagate that Vr and Vf
without loss to actually establish standing waves you could measure.
I agree with Bill that all this is academic, but my working definition
seems to me to be consistent with the _concept_ of SWR, and does not
require me to be changing horses in mid-stream and remembering when to
use a conjugate and when not to. I _NEVER_ use Zo* in finding rho.
To me it's not so much a matter of nitpicking an area of no real
practical importance as coming up with a firm definition I don't have
to second-guess. Except on r.r.a.a., I don't seem to ever get into
discussions about such things, but my definitions are easy to state up
front so anyone I'm talking with can understand where I'm coming from
on them.


W.C. Johnson points out on page 150 that the concept:

Pload = Pforward - Preflected

is strictly correct only when Z0 is pure
resistance. But the calculations of real power
into the coax and real power into the load are
valid and the difference between the two is the
real power loss in the coax. For these
calculations the complex value Z0 for moderately
lossy coax is useful and adequate.

The preoccupation with VSWR values is unfortunate
and excruciatingly exact answers involve more
nitpicking than is sensible.

Agreed! And thanks for the reference re powers.

Cheers,
Tom