At 10:17 PM -0400 7/28/03, Pete Smith wrote:
>With the teflon dielectric, is cold flow really an issue?
I've seen fiberglass-reinforced Teflon(R) circuit boards (diel.
constant about 2.2), about 0.031 inch thick, cold-flow. They were in
a microwave receiving antenna, inside an unventilated translucent
plastic radome, on a roof in Sunnyvale, California. Apparently the
radome functioned as a greenhouse. I don't know how high the
temperature got inside it, but I do know that these circuit boards
had very little stress on them -- just their own weight. But, over
the course of one summer, they sagged horribly. I wouldn't have
believed it if I hadn't seen it.
When coax is wound on a toroid, the center-conductor puts a lot of
stress on the dielectric.
73 -Chuck, W1HIS
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