[Antennas] Expanding foam and antenna tunning

[Cletus W Whitaker]

de WB2CPN South Central Pennsylvania    2002.08.27

Usually the amateur community doesn't run enough power to encounter
heating of diaelectrics, but it is a very real thing.  I've seen 
VSWR on resonant antenna transmission lines cause noticeable warming
of ceramic insulators when the voltage at their location got very high.
Not conduction heating, but stress heating.  Of course, all ceramics 
are not the same.  Mica products were the least affected.  When I
worked with radar in the 40's we used common clean sand for a dummy
load.  The point is; at high voltages, insulators act strange.
                 73  Clete