On Thu, Dec 27, 2012 at 10:12 AM, Ashton Lee <ashton.r....@hotmail.com> wrote:
> Several of us here in Western Colorado run slopers off the tower, which I > believe is essentially loading the tower with an elevated lead. It works > for us. Sloper is really not the same thing as a parallel vertical wire at four feet as with the original poster. The vertical wire parallel to the tower at four feet has a much higher degree of coupling to the tower than your sloper. The tower is induced to a degree either way, but if the tower to dirt resistance is high, the impedance of the sloper is not changed nearly to the extent that the L's is. The close coupling of the L works harder on the tower's base resistance. This is very easy to model. Varying a load resistance at the base of the tower in either case will show the dependence of either antenna. The worst losses occur when the tower, plus all its antennas viewed as top loading, is close to natural resonance on 160. Once the tower current gets down to a third or a fourth of the current in the driven antenna, the antenna should be out of the deep woods for induced loss. As usual, those with really good conductive dirt are far less affected than those with poor soil. It is a very good exercise to model the tower and its entire antenna and its conductors, along with all the other antennas, with feedlines explicitly included. Once you get that model done, a bit of a PITA the first time, you hang on to it, and keep it current. You turn on the feedpoints (EZNEC "sources") one at a time and see what happens. There should be a "load" in the bottom of the tower to account for the base resistance to the dirt. The devil is in the details. Some folks come out fairly clean, others have surprising interactions paid for in loss. If you are the latter, it's a very useful thing to know. 73, Guy _______________________________________________ Stew Perry Topband Distance Challenge coming on December 29th.