Reg wrote:
"For 100 years or more, new multipair phone and other cable types have
been acceptance tested with reflection coefficient bridges. One pair in
the cable is exhaustively tested for everything the test engineer can
think of to make sure there`s nothing wrong with it.."

Why bridge test a cable pair that has continuity and accessible
terminals?

I would rather measure the transmission characteristics that I might
use.

The impedance of a 2-wire circuit may be of interest for balancing a
term-set, but that is usually accomplished by adjusting the balance
network by trial and error for the best balance or for most transhybrid
loss. Another option is to accept a compromise fallback network which
gives whatever hybrid balance results, good or bad.

One can locate a line fault by using:
wavelength = V / f

Where multiple repeaters are in a chain, as in Reg`s undersea cables,
each repeater can generate its own unique pilot tone. One can check the
tones to determine where the chain is broken. I`ve done that with
terrestrial microwave systems and recorded the tone interruptions on a
multichannel event recorder with synchronized timing marks. Whenever an
outage occurs, time, location, and duration are charted.

For a rough check on local telephone loops in the swirtched telephone
system here, the phone company had a dial-up tone oscillator in its
central offices. More significantly, other subscribers can be dialed up
to determine the quality of the connections that can be made.

Data circuits often have a loop-back capability in data modems, used to
determine error rate. This is another way to evaluate circuits.

For broadcast program lines, and other leased circuits, the phone
company will treat the line to meet specifications. The customer then
tests his own circuits to make sure he is getting what he pays for.

There are "silent" test systems for multipair cables which test with
tones outside the audible range. These can evaluate attenuation and
cross-talk and these can be related to the similar values in the audible
range.

SWR is a function of reflection strength. I see no problem in labeling a
reflection strength as SWR, even though there may not be enough cable
for a standing wave pattern. I think TLI would be a fine meter name too.

Best regards, Richard Harrison, KB5WZI