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## [TowerTalk] Rotator and Antenna Standards

 To: [TowerTalk] Rotator and Antenna Standards n4zr@contesting.com (Pete Smith) Mon, 01 Mar 1999 13:05:50 +0000
 ```Once again, the question of sizing rotators to a given antenna(s) has come up. I'm not an engineer, so please excuse me if the terminology in what follows is not 100% correct, but I think the question is worth asking. The K-factor as defined by Yaesu is a step in the right direction, but we should be able to go further in determining whether we have enough rotator. As I understand it, the product of turning radius times total weight is a conservative and easily calculated measure of the mechanical inertia/momentum that a rotator must overcome to start and stop turning an array. The trouble is that it doesn't tell you very much about real worst case, when wind is opposing either the starting or stopping of rotation. Force 12 quotes a worst case mast torque for each of their antennas, based on a 70 mph wind blowing at the angle that is calculated to produce the most torque. Why couldn't one combine such a figure with a MEASURED mechanical inertia (the real equivalent to the K factor) to come up with a single "rotator load factor" for a given antenna? My pair of Force 12 antennas on a Yaesu G-1000SDX have a "K-factor" of 1127 foot-pounds total, well within the G-1000's rating of 2020 foot-pounds. The total maximum wind torque is 40.8 foot-pounds. The rotator is rated for a braking torque of 434 foot-pounds, and a rotating torque of 43.4-79.5 foot-pounds. Since both numbers are comfortably within spec, this rotator should have no trouble turning or stopping this array, and in fact it doesn't. but I'm uncertain how far one really can push it, and many people will have more aggressive antennas than I do. Question for the MEs out there -- how would you combine wind torque and measured inertia/momentum to produce a real number, that could be compared with rotating and braking torque specs to determine if a given rotator will do the job reliably? 73, Pete Smith N4ZR n4zr@contesting.com Loud is. -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
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