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## Re: [TowerTalk] 80m 4Square Dipole VSWR question

 To: "Yo3ctk" ,"Paul Playford" ,"'D. Rodman, MD'" ,"'towertalk'" Re: [TowerTalk] 80m 4Square Dipole VSWR question "Tom Rauch" Tom Rauch Thu, 18 Nov 2004 08:08:48 -0500
 ```> I read from your comments that the Comtek box doesn't work and cannot work. > Is my reading correct? No, I never said that. It's obviously a good system, many people use it and have been using it for years. My only point is people look at these systems and assume they can take the classic base impedance of a lossless vertical translated through 1/4 wl of coax and that is what the box sees. That very obviously isn't true. Phased arrays like this don't behave that way, unless they have terrible loss. (To make everyone happy, if you add a great deal of loss resistance the elements get very close to the same impedance because the loss swamps out mutual coupling. Since most people don't want that on transmitting arrays, I'll ignore that.) My points are only these: The impedance of forward, rearward, and center pair elements in a 4-square are all different. If you change the elements, you can't simply recalculate based on the "dry" impedance of one element. The power fed to each element is different. Current fed antennas require equal current in each element, voltage fed antennas require equal voltages to produce a deep null and near-maximum gain. If the pattern desired is a classic pattern, the power to the element ports (the center element feed pair are the same) is obviously significantly different. A lack of heat in the dump resistance of a hybrid really does not tell you the array is behaving like you might think it is. Consider the case where people insert coax in series with a feedline to "phase" an array. Unless that coax is an exact multiple of 1/4 wl, the electrical length of that cable will not equal the phase delay unless the cable is terminated in its surge impedance. Very few people who have 1/8th wave spaced antennas with 3/8th wave coaxial delays actually have 135 degree delay like they think. Those are the only points I'm making. I have no idea how the Comtek box works because I've never owned one. I only know how phased arrays and phasing systems work. Maybe someone has characterized the Comtek box, and knows what port terminations it likes to see. Whatever it is, it probably is not the uncoupled impedance of the elements transformed by the 1/4 wl cable. 73 Tom _______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread Re: [TowerTalk] 80m 4Square Comtek box, (continued) Re: [TowerTalk] 80m 4Square Comtek box, Michael Tope Re: [TowerTalk] "Buying stuff", Malcolm Ringel Re: [TowerTalk] 80m 4Square Comtek box, Tom Rauch Re: [TowerTalk] 80m 4Square Comtek box, Jan Erik Holm Re: [TowerTalk] 80m 4Square Comtek box, Jan Erik Holm Re: [TowerTalk] 80m 4Square Comtek box, Jim Lux Re: [TowerTalk] 80m 4Square Comtek box, Jerry Muller Re: [TowerTalk] 80m 4Square Comtek box, Jerry Muller Re: [TowerTalk] 80m 4Square Comtek box, Frank Mayer Re: [TowerTalk] 80m 4Square Comtek box, Jim Lux Re: [TowerTalk] 80m 4Square Dipole VSWR question, Tom Rauch <= Re: [TowerTalk] 80m 4Square Dipole VSWR question, Jim Lux