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I thought I would share this with everyone because I really should have known better! On Friday night a very strong front came through upstate New York with winds in excess of 66 mph at my hilltop QTH. During this wind attack, my stack of two C3E's on a rotating pole stopped playing antenna. This meant that I had the "honor" of doing the DX contest with a ground mounted vertical instead of the stack. Today, I went outside with a friend to fix the stack and we quickly isolated the problem to the coaxial cable running up the tower between the Heliax and the Stackmatch. I immediately cut off the ends to put new connectors (one an "N" and one a PL259) and was simply shocked to see that the nice new cable installed last spring was 9913 with its solid conductor. A dummy load and an analyzer quickly determined that the cable had failed. A quick slice session with a case knife located the problem spot where the center conductor had pulled apart after breaking. The solid center 9913 had been installed with a large loop at the bottom of my pole (called Stosh) and was attached with strain relief at the top AND was prevented from swinging in the breeze by a Rube Goldberg adaptation of a rope harness attached to the top of each telescoping tower section. The failure occurred due to the flexing of the rotating pole, not the turning of the tower as the rotor is at the bottom. The wind storm of one month ago (82 mph winds) and the weekends blow were enough to flex or bend the tower repeatedly, therefore moving the attached 9913 and ultimately twisting the solid center insulator apart. What I have learned from this event is never to use 9913 with a solid center conductor in an application where any movement can be encountered. I know a rotor loop of RG213 or RG8 is needed after using 9913, but I never thought subtle repeated movement would lead to failure. Even though the 9913 was secured to the pole, there was enough movement to cause failure. 73 Natan W6XR/2 -------------------------------------------- Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. Force 12 Web site: http://www.qth.com/force12 Submissions: send to Force12Talk@qth.com To unsubscribe: send a blank e-mail to Force12Talk-leave@qth.com Force12Talk Message Archive: http://www.qth.com/force12/list/force12talk For problems with the list, contact n4zr@qth.com |
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