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I had a two stack of C31's on Rohn 25 for a couple of years. One at 74' and one at 33'. It performed extremely well. The lower one was mounted on a homebrew sidemount, the C31 was stretched one foot and I had a full 300 degree rotation. A regular C31 will NOT rotate 300 degrees even on Rohn 25 without being stretched or using a Tic. I used a ham type rotor on the lower mount. Stacking modeling is available from Force 12 so you may want to check with Natan or Tom on that. I found them to be extremely helpful--first class. Recommended spacing is 30-40 feet but I don't have the model handy. I think 35 is the preferred happy medium distance. However, we did some modeling and just don't see much difference in 30'. I currently have moved up to a three stack of C31's on 110' of Rohn 55 with a Mag 340 and 180B on top. My personal method is to use typical graph paper, taped together to make a very large sheet and then scale the tower, guys, guypoints, antenna turning raduis, etc. My results turned out to be very accurate using that method. If it were me I would put the C31's at 35 and 70 or 30 and 65 and use the top (90') for something else, 40M rotatable or two element or ??. This may give you some clearance help. This is a real load for the Rohn 25 so be aware of the windload. I never had a problem but your situation may be different. I did have it guyed at three levels, the distance to guypoint is 64', originally calculated for an 80' tower. I am on an 800' hilltop with terrific 100-300' slopes in all the right places so this played a role in my selection of the tower and stacking heights. Of course, so much depends on your location, height etc. Bottom line, two C31's on Rohn 25 was a killer setup here, absolutely no problems. Hope this helps some. 73, Tommy WD4K -----Original Message----- From: Burton, Bob (by way of Pete Smith <n4zr@contesting.com>) [mailto:Bob.Burton@McKesson.com] Sent: Thursday, March 06, 2003 3:31 PM To: force12talk@qth.com Subject: [Force 12 Talk] FW: C31XR stack? I currently have a C31XR on 90' of Rohn 25G (actually 88'). The guys are at 28', 56', & ~84'. I picked up a second used C31XR locally with potential plans to stack them, however this may not be possible on the current tower. Due to the 80% guy distance (72') if I put the second C31 at 56' I don't think it will clear the top guy. No, I can't move the guy point for the top guy wire out. Also I'm a also bit concerned about the wind load on 25G, though I've seen 3 TH7's on 100+' of 25G before. Curious if anyone has done this and if it will in fact fit. Otherwise an alternative is to put the second C31 on another tower at a lower height (likely 40-60'). I wondered if anyone has an EZNEC model for a C31 they'd be willing to share since if this is the approach I'd like to optimize the height of the second C31 on the separate tower to fill in the nulls of the current C31. Granted the stack would be more flexible but if it won't fit, it won't fit and it looks too close to me on paper. I'd also like to hear from anyone who has stacked a C31XR and a C3E as the smaller C3E would fit on the 25G and could go on a 300 degree swing gate instead of a ring rotor. Thanks for your input. 73's Bob - N4PQX -------------------------------------------- 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 -------------------------------------------- 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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