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It's very possible that your tower is resonant as a 1/2 wave on 20 or 1/4 wave on 40. With 7' of separation, that is about the typical distance for a 20m parasitic element. It's a bit close for 40m spacing, but there could still be strong coupling on 40m to your tower. That said, I would still think you should be able to achieve a match by adjusting the T-bars on 20. Have you done this? Adjusting the 40m coils can sometimes be very tricky - it's easy to overshoot your target frequency with small adjustments of the coil. It's quite possible that the default settings will not be valid if the antenna is strongly coupled to the tower. If you have adjusted the T-bars on 20m and still cannot get a good match, I think it lends further credibility that you are coupling to the tower. If so, the impedance of the XK on 20m is probably much lower than it's designed for. If so, you might need a hairpin across the feedpoint. That said, I have installed a number of 2 ele Sigma verticals, and we do not need a hair pin. If you cannot get a good match, I would suggest moving the vertical as far from the tower as possible. But I assume you have already considered that, and it's not possible. 73, Kenny K2KW Team Vertical ----- Original Message ----- From: "Kjeld Holm" <kh@kh-translation.dk> To: <force12talk@qth.com> Sent: Friday, November 07, 2003 11:06 AM Subject: [Force 12 Talk] RE: Sigma 40XK > Hello All, > > I just installed the Sigma 40XK on a wooden structure on my lawn close to a > brick house and with the lower T-bar 7 feet (2 meter) up for the purpose of > been able to walk on the lawn below it. The antenna is also just about 7 > feet from a 18 feet tower (metal) with 4 x 6 elm for 2 meters. > > On 20 meters I have SWR 1:2.5 at the bottom of the band slowly rising to > 1:2.8 at the upper band limit. Is this what I have to expect being so close > to other structures? Or do you have any suggestions? > > On 40 meters I spend some time fidling wiht the coils but could not get any > resonable results that's why I resort to 20 meters. > > PS The manual says SWR 1:1.3 for 20 meters. > > Vy 73 > OZ1CCM Kjeld > > > > > -------------------------------------------- > 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 force12@qth.com > -------------------------------------------- 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 force12@qth.com |
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