The back-lobe structure in Fig 2A indicates approximately a 4- to 5-dB variation as the antenna rotates. (patterns modeled with NEC at 14.2 MHz, over ground with a dielectric constant of 10 and a conductivity of 13 millisiemens per meter)įigs 2A and 2B show patterns for the lower Yagi. The main lobe (at about 9°) is not disturbed at all. The horizontal pattern (A) shows very little disturbance the vertical pattern (B) shows trivial change in the back-lobe structure. The forward main lobe at about 9° - the one we communicate with - is not disturbed at all.įig 1 - Modeled patterns for the upper Yagi (height, 109 feet). As most of the variation occurs at attenuations greater than 30 dB, this effect can be considered trivial. The horizontal pattern (Fig 1A) shows very little disturbance the vertical plot (Fig 1B) shows some change in the hack-lobe structure.
(The 0° plot places a set of guy wires directly on the Yagis' boresight.) Because the guy geometry repeats after 60°, five modeling passes are sufficient to show the guys' effect on the antennas as they rotate 360'.įigs 1A and 1B show patterns for the upper Yagi. I plotted the antennas' horizontal and vertical patterns at guy-position intervals of 15° from 0° to 60° off boresight. I chose a 0° to 180° linear plot over the more common polar plot to allow detailed side-lobe examination at higher-than-usual pattern attenuations. (2) I modeled the ground beneath the tower as exhibiting a dielectric constant of 10 and a conductivity of 13 millisiemens per meter.įor graphing the results. (This arrangement is similar to the 20-meter antenna situation at my station.) I modeled the antenna elements as perfect conductors, dividing them into an adequate number of segments for NEC analysis. The antennas on the tower comprise two simplistically designed five-element Yagis on 58½-foot booms, one mounted at 54 feet the other, at 109 feet. Using NEC, (1) I modeled a 109-foot tower constructed of Trylon AB-I05, with conductive 'A-inchdiameter guys connected between the tower (at 53 and 103 feet) and three ground anchors spaced 70 feet from the tower's center. I decided to computer-model the antenna-pattern degradation (if any) attributable to continuous, conductive guys. Option 3 is by far the least-expensive approach - but what about the warnings of ham lore? What does Option 3 cost in terms of antenna performance? Also, the cost of Option 2 is now approaching that of Option 1. I have used Option 2 many times, but with the addition of the 10, 18 and 24-MHz bands at WARC-79, it's difficult to find a guy-segment length that does not resonate in at least one of the ham bands between 3.5 and 29.7 MHz.
I hope that the following analysis will dispel some of the myths about conductive guying. In contrast, I recall that, a number of years ago, the builder and owner of one of the most successful contest stations in the world, Ed Bissell, W3AU (ex-W3MSK), did not use insulator-segmented guys on some of his towers - and his signals were legendary throughout the world on all bands.Ĭontinuous, conductive guys - no segmentation, no insulators - currently support two of my nine towers, and I observe no discernible per%onm-re degradation attributable to their presence. Ham lore has long preached that tower guy wires not broken up into short, nonresonant lengths by insulators will significantly degrade the performance of antennas on the guyed tower. Now, computer modeling reveals that unbroken guys can work just about as well. Radio amateurs have long worked to preserve antenna patterns by installing segmented, nonresonant guys. Home - Techniek - Electronica - Radiotechniek - Radio amateur bladen - QST - The effect of continuous, conductive guy wires on antenna performance
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