Tom, what I suspect is the fact that the foam is not tough and that the center
conductor can slowly ooze away from it's center alignment, especially if the
coax is strongly coiled or bent... High temperatures, sunlight heating, etc.,
will soften the foam and make the drift happen more rapidly... I have seen the
occasional piece of foam coax on my own station where the center conductor
was pushed sideways almost to touching the braid <one was a piece that was
accidently kinked around a rotor... While I did not bother to do a VF
measurement I know that the changed geometry will have to affect the VF... I
suspect this is what is being warned about in VF critical applications...
denny / k8do
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