[Lowfer] WC2XSR/13 rain problems today

[Bill Ashlock]

Ralph,

Very interesting reading! First you were Ben Franklin, then Nicola Tesla, 
now, from this account, Robert Fulton. What next?

Bill A

>I had an interesting afternoon, standing in the rain and watching sparks
>fly!
>
>At about 1500 CDT today, the transmitter PA current began taking erratic
>dips for several seconds. Simultaneously, the RF forward power dropped
>from 400 watts to 100 watts, and the reflected power went up from 10
>watts to 100 watts, a sure sign of either a shorted or an open feedline.
>
>Since it had just begun to rain, I thought the cause of these current
>changes might be an arcing condition in the antenna system. An
>inspection of the antenna showed nothing wrong, but the static gap at
>the output of the antenna tuner was intermittently flashing over. There
>was no lightning associated with this rain event, so I watched the gap
>for a while to see what was happening.
>
>After watching the static gap for a few minutes, I saw the cause of the
>arcs. As rainwater ran down over the grounded leg of the static gap, the
>water tended to collect and form hanging droplets on the underside of
>the flap portion of the horizontal leg of the gap. After a few moments,
>they would grow large enough and drop to the ground. If the droplet
>reached critical size, and just before it fell away from the gap leg, if
>the transmitter turned on at that moment, the high electric field would
>attract the water droplet into the narrow portion of the gap itself.
>This water intrusion into the gap would substantially reduce the
>effective gap spacing, triggering an RF power arc, which would remain
>there until the transmitter turned off again or the water drop
>evaporated due to the heat of the arc. I will have to install a plastic
>rain shield to prevent this in the future.
>
>Another interesting thing was observed as well. After about 10 seconds
>of the transmitter turning on with the QRSS30 modulation, I observed
>what appeared to be smoke rising from the area of the static gap. Closer
>inspection showed that it was not smoke, but steam!
>
>Apparently what was happening is that during the off periods of the
>QRSS30, the ceramic bowl insulator was becoming wet from the rain. When
>the transmitter turned back on, the RF is heating the bowl insulator and
>the water enough to create the steam cloud I saw. I will have to observe
>this in the dark so that I can determine how much of the heating is
>caused by dielectric loss in the ceramic and how much is caused by
>surface corona discharge. This is just another interesting item that I
>have noticed while working with high power LF energy.
>
>73,
>
>Ralph   W5JGV / WC2XSR / 13
>
>http://home.att.net/~shmrg
>
>http://home.att.net/~ralph.hartwell
>
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