Cecil Moore wrote:

And if you will remember, the original question didn't involve the
SWR meter at all. The question was: Are my 2-foot sections of RG-400
connected to my SWR meter long enough to ensure that the SWR meter
reading is valid for the coax? Remember that argument?

The threads for the past few days have all diverged from that
original question which was:

How long must the 50 ohm coax connected to the SWR meter be
for the SWR meter to report a valid SWR *on that coax*? The
answer obviously cannot be zero length.

Cecil,

What has become quite clear from this lengthy thread and the experiments
reported is that what you seek is impossible. The design and physical
configuration of the Bird 43, and probably most or all simple SWR
meters, is such that the measurement is completely unaware of the
external "environment". The Bird 43 correctly reports system mismatch,
such as that from a load that differs from 50 ohms, but it ignores any
artificial mismatch from the adjacent coax.

A report of the valid SWR *on that coax* will happen only by
coincidence. The meter does not care about the length. Zero is just as
good an answer as any other length.

And who would really care to know such a thing? The unknown of interest
is generally a load or matching device, not the improper coax.

If you really need to know the "valid SWR" on the mismatched coax you
are going to need a different technique and instrument.

73,
Gene
W4SZ