As Tim noted I built the K3LR version of the 3 element parasitic array this past fall. I used my original and existing shunt fed tower as the driven element. It is switchable in four directions and I have an extensive radial system (120 radials)under each element.
My initial assessment indicates a forward gain of around 5 dB and a minimum F/B of 25 dB. It performs very well from out here in fly over country. I am in the process of completing a paper detailing my construction and experience with the array and will also be presenting this at the Dayton Antenna Forum on Friday of Dayton. I have spent the past 10 years improving my 160 meter RX systems here at W5ZN and had reached a point of needing to improve the TX system beyond a single shunt fed tower. I struggled with whether to build a stand alone 4 square for 160 meters however the appeal of the parasitic array is that I could use the existing shunt fed tower to support the T elements without having to erect an entirely new mechanical structure for a 4 square while achieving basically the same result. I have been pleased with the performance for the short few months it has been in operation. Obviously it doesn't provide the broad bandwidth a 4 square does. I have about 40 KHz between 1.5:1 points however in reality a 4 square has limited bandwidth since beyond the resonant points you dump a lot of power into the dump load! 73 Joel W5ZN > I have been using a 3 element parasitic vertical beam on 160 for at least > 20 > years. K9CT, NR5M, AA1K*, VE3EJ and most recently W5ZN have the same > array. > It has instant switching in 4 directions. > > With 4 parasitic cut directors around the center driven element tower - it > is pretty easy to get over 5 dB of forward gain (over 40 KHz wide) and > over > 30 dB of front to back (over a narrow bandwidth). Easy driven element > match > with an L network at the base. Each parasitic has 3 modes. Director, > Reflector or float. Going from directional to Omni is easy as well. > > *AA1K has an additional director toward Europe. So he has 4 elements! > > As was pointed out - the magic in any vertical antenna is all about the > radials. Each parasitic wire (4) and the center driven element tower has > 120 > radials that are 130 feet long (unless they cross the junction bus). I > have > 67,000 feet of radials under my 160 array. > > I use a 120 ft 24 inch face solid leg tower as the driven element. The > tower > sections are welded together to decrease any joint loss. The parasitic T > wires are #12 Copperweld. > > The last three editions of the Low Band DXing book describe this antenna > in > the Yagi chapter. > > 73 > Tim K3LR > > -----Original Message----- > From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of W7RH > Sent: Tuesday, January 30, 2018 11:39 PM > To: Topband > Subject: Re: Topband: Adding a parasitic reflector to a vertical > > I've played with parasitic elements in antenna arrays for almost three > decades and the current antenna system I have used parasitic elements > both director and reflectors. > > With very careful tuning performance that of a all driven array can be > achieved. Tree is correct they due tend to be somewhat limited in in > bandwidth with relation to F/B ratio. Gain remains fairly constant. > > The tuning procedure that Tree suggested is absolutely correct. You > detune all unused elements and adjust the center frequency of the > parasitic for best F/B one element at a time. Parasitic elements I might > add are no different than driven and must have extensive ground system > to be effective. No exceptions. You know you have right by F/B ratio. > You can go one step further and measure the actual antenna currents > which I have done. In my system the parasitic elements achieve 80-85% of > the theoretical current at the base. > > de Bob W7RH > > > > > > > > > > > > > > > _________________ Topband Reflector Archives - http://www.contesting.com/_topband