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We at the TRW radio club bought an EF 180C 80 meter dipole several years ago and presently have it mounted about 60 feet above an industrial building rooftop having a number of metal airconditoning and elevator housing sheds on it. We found that the bare antenna resonates around 3.6 MHz instead of 3.8 MHz where it should. We have tried everything we could think of to resolve this problem short of bringing the dipole down. For example, we rotated the antenna to see if that made a difference (it didn't), we tried spreading the hairpin matching stub--it raised the minimum SWR at resonance and broadened the 2:1 bandwidth somewhat but did not change the resonance much. We tried moving the shorting wires and that made a few KHz difference but not 200 KHz. We also made photographs of the antenna and measured its length and found the photogrammetric measurements to be within a few per cent of the advertized value. Lastly we noted that the 2:1 bandwidth was about a factor of 2 too narrow; e.g. about 50 KHz instead of 130 KHz as advertized. Are there any hams out there that has noted this behavior with their 80 meter EF 180's??? If so, how did you fix it?? 73's Peter W3CRI -------------------------------------------- Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. Force12 Web Site: http://www.force12inc.com To Submit Message to the List: Force12Talk@qth.com To unsubscribe and view the Message Archive: see http://qth.com/force12/list For problems with the list: contact n4zr@qth.com |
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