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Didn't know this would stir so much up... Well Jim, VE1JF, started talking to me about the feedline lengths. I think he has looked at this issue, because of his stack going up this summer. In my senerio the C-31XR & C-51XR are identical antennas from 20-10, but there is a feedpoint displacement of ~9'. In running some of the AO models and using the "does this sound reasonable" test. The phase shift of the C-31XR is around +90 degrees out of phase on 10 meters (remember the C-51XR feedpoint is in front of the C-31XR). Now I had to use my buddy John, K9UWA, to do the calculations with the C-3E, because he is the only one I know with AO-Pro (no segment limits - only memory). He came up with the following results for 10 meters: C-51XR @ 0 phase C-31XR @ + 90 degrees C-3E @ +114 degrees I have had numerous conversations with Jay, WX0B, and he agrees that once the feedline lengths are calculated, they should be the same for all bands (20, 15, & 10 meters). I did use NECwires to test the phase results and the improved signal strength of adding the C-3E to the mix was less than 1 Db. The biggest improvement was the big high angle lobes are mostly gone and the primary lobe is around 6 degrees (this is with all antennas fired up). I can go to any individual or a 2 antenna stack combination and get higher angles too. Currently all my feedlines are the same length (I was in a big hurry to get the antennas up before the snow) and I have done some testing with a local ham ~ 1/4 mile away. Even with the feedline lengths the same, there is still 2-5 Db gain over any single antenna on the each band. I am still experimenting with the numbers, because I want to be sure before I start adding or cutting coax on the tower! My biggest problem is a faulty relay for the 40 meter beam on the C-51XR and if you haven't seen this antenna, the feedpoint is about 10' out from the tower!! The solution is to take all the antennas down :( or to get a crane ($$$.$$). Either way I pay (with time or $$). Tom did have a joking suggestion to climb out on the boom 4" thick wall, but I don't have the guts!! I even offered to pay for him to come and do it :), I probably could have sold tickets! 73's, Kevin WN9O >"Natan Huffman" <force12e@lightlink.com> wrote: >Pete, > >That was done by Dan Levin with help from L.B. Cebik. > >NH ----- Original Message ----- From: Pete Smith <n4zr@contesting.com> To: <force12talk@qth.com> Sent: Wednesday, February 23, 2000 1:27 PM Subject: Re: [[Force 12 Talk] Why I bought my 54 F12 elements ] > At 11:37 AM 2/23/2000 -0500, Natan Huffman wrote: > >Kevin, > > > >I noticed in your post you stack a C51XR/C31XR and C3E. For practical > >purposes, the C31XR and C51XR are identical, but the C3E is not. Did you > >make any adjustments (such as length of coax to compensate for phase > >differences) or just "brute forced" the feeding of the C3E. Stacking non > >identical antennas can be challenging! Or, perhaps the C3E is not par t of > >the XR stack. > > > >We are often asked about this type of scenario but just have not had t he > >time to do a good analysis and develop a recommendation. > > There was a post within the last couple of months on Towertalk about th is. > If I remember the particulars correctly, this person had stacked one of > your multiband antennas with the closed sleeve feed system, with a straight > yagi with split dipole feed, and used NEC-2 and lots of trial and error to > calculate the phase shift that was required to achieve pattern addition . > The number was striking, I remember -- ~ 160 degrees. He said it then > worked roughly as predicted. > > >From some other things I've read, I'm now wondering if this analysis w as > good or not, since NEC-2 reportedly has trouble with modeling this type of > feed. Nonetheless, a thought. > > 73, Pete N4ZR > > Don't forget to update your entry in the World Contest Station Database > http://206.102.70.3/search.htm > > > ---------------------------------- > Force12Talk mailing list provided as a service by Force 12 Antennas, In c. > Force 12 Web site: http://www.qth.com/force12 > > To unsubscribe, send a blank e-mail to force12talk-leave@qth.com > For problems with the list, contact force12@qth.com > > Get free email and a permanent address at http://www.netaddress.com/?N= 1 -------------------------------------------- Force12Talk mailing list provided as a service by Force 12 Antennas, Inc. Force 12 Web site: http://www.qth.com/force12 Force12Talk Message Archive: http://www.qth.com/force12/list/force12talk To unsubscribe, send a blank e-mail to force12talk-leave@qth.com For problems with the list, contact force12@qth.com |