Fire

Last week we were doing some HF radar observations at EISCAT to study polar mesospheric winter echoes and to try out magnetospheric radar. While tuning the antennas for the experiment, I got a call from my colleague at EISCAT, who indicated that there was a "hell of a lot of smoke" coming from the antenna field. We quickly turned of the transmitter and ran into antenna field. It was very easy to see where the problem was, we just had to follow the smoke. It turned out that one of the antennas had a faulty ladder feed line, which had a conductor that due to mechanical stresses weakened during many many years of flapping about in the wind. The connection was so bad, that the resistive heating of the weak point caused the feed line to go up in flames. The fire was quickly put out, the problem fixed, and the experiments could continue.

Basic lesson of antenna theory: if you put 1 kW of RF through a broken feed line, it can catch fire.

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