[TowerTalk] RG303

[Chuck Counselman]

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