... Anything other than 50 ohms indicates a problem.
And 50 ohms may also indicate a problem.
When coax gets waterlogged, the loss increases,
but the characteristic impedance stays about
the same. (Often the loss is due to the corrosion
between the individual strands of the braid, so
it doesn’t act as a solid conductor.) The higher
loss will
improve the SWR at the rig, because
there is less reflected power that survives the
round trip to the antennaand back.
One way to test a cable for loss is to measure
the SWR at one end with the far end open or
shorted (and preferably both, then average
the readings). The
lower the SWR, the
higherthe loss in the cable.