[TowerTalk] Water in matching sections

[alsopb]

Guys,

I finally unraveled a mystery that has plagued me for almost two years.

Every winter the SWR on my 160 meter inverted L would go crazy after a
hard freeze. The symptom -- low power SWR a bit high but it climbed a
lot when high power used. The first thought -- water in the coax
somewhere.  After many tries at trouble shooting with an RF analyzer,
replacing sections of coax, redoing connectors, a permanent fix was not
found.  Of course, the problem went away if the temperature got
significantly above freezing....  

Today I found it (I think).  In the L-network matching section I have
there is a 350mmfd variable capacitor mounted vertically.  Although the
box is watertight, there were water droplets between several sections.
Blowing it away caused the problem to go away!  It appears that frost
forms on the plates, melts and forms droplets.  I guess the solution
will be to mount the cap horizontally so that the water will drain or
replace it with a fixed value cap.

Who would have thought.....

73 de Brian/K3KO

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