Good afternoon.
Appreciate your asking about this situation. The condition of the PVC
melting on the 20 mtr reflector cannot happen under typical operating, even
running several KW. If any element would have a problem, it would be the
driver.
An important question is, "What happened when it "melted"?
The reason this is important is because the antenna will work the same. It
does not matter if the reflector is insulated or not from the boom. It can
be either insulated OR grounded to the boom. Insulated or not, melted or
not, the reflector will still operate properly. The issue of the PVC melting
indicates something else is happening.
The driver element in the 20 mtr portion of the C-3XL will have 100% of the
maximum current. This 100% will occur right at the center of the driver. The
reflector has about 49% of the maximum. The director has about 47% of the
maximum. This gives us a clue. Something happened to the reflector center
insulator. Nothing happened to the driver, which has twice the current.
We need to look for some unique condition here.
How could sufficient current flow from the element through the PVC to melt
it?
The only way that comes to mind is to have an external source. Two
suggestions are:
1) look at the antenna to see if the reflector element (i.e. the tip)
is coming into contact with something. For example, maybe an AC high voltage
power line that can pass high current/voltage through the element, through
the PVC, to the boom, to ground.
2) ground the reflector directly to the boom. Whatever is causing this
strange condition will then have a direct path to ground.
Hope to know what is the cause.
Have a good day and 73,
Tom, N6BT
Force 12 Antennas and Systems
(Home Page http://www.QTH.com/force12 )
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