I took the faithful Simpson 260 and measured the resistance across the coax. It measured 47-ohms (more or less). I had ruled out everything except the phasor, or had I? I decided to check the antenna at its operating frequency, just to make sure. I located the station's impedance bridge, which was made in the 1950s by General Radio, and connected it to the coax going to tower 4, which still had the 47-ohm resistor.
The bridge had two large dials with one marked
"X" and the other marked "R." I connected a signal generator to the bridge and set it to 1MHz, which was the approximate frequency of the station. I adjusted the dials for a null and both "X" and "R" read zero. I wondered if the impedance bridge was defective, so I put a 47-ohm resistor across the terminals of the bridge and "X" still read zero, but "R" read 47. At that point, I knew the cause of the problem.
I asked the chief engineer if he had checked the pressure on the cable lately. He had not, and after examining it, the pressure meter told me that there was no pressure in the cable. I had him pressurize the cable and then I walked out to the tower. I removed the setscrew at the distant cable fitting and water squirted out. Once the water was cleared from the coax, the antenna worked properly.
This entry was submitted by Frank Karkota and edited by Jennifer Campbell.
Frank Karkota worked with power transmitters in the range of less than 1MHz to 5GHz. He designed and built equipment for radio stations and eventually started a company that made commercial and consumer receivers that covered 500kHz to almost 1GHz.
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