Topband: Adding a parasitic reflector to a vertical

N7DF n7df at
Mon Jan 29 13:40:41 EST 2018

>From southcentral New Mexico working Europe on 160 meters is pretty much an exercise infrustration with a single vertical antenna. So I decided to see if I couldimprove on things by adding a parasitic reflector element to my cage antenna.  Since I could not find any specificinformation about doing this I decided to experiment a little and see what Icould come up with.  After looking at a lotof designs for two element antennas and taking into consideration the physicalparameters of being in a juniper forest I finally came up with a design that Icould build.  My antenna is a Collins27W-1X conical monopole fed with an MFJ 998 remote tuner located in a 120 footdiameter clearing. The parasitic reflector would be 88 feet southwest of the monopolein a small clearing.  From what I coulddetermine from various sources, in order for it to be effective at thatdistance, it would need to be resonant at 1.787 MHz to provide maximum gain at1.825 MHz.  The reflector elementconsisted of a 30 foot tall section of 2 inch diameter irrigation pipe restingon a plexiglass sheet with a top hat wire strung at right angles to the linebetween the transmitting antenna and the reflector.  In the opposite direction a ground radial waslaid out along the ground surface.  Aftera lot of measuring with an antenna analyzer and cutting to length the top hatwire ended up as 86 feet 4 inches long and the ground radial at 112 feet 3inches to get resonance at 1.787 MHz. The bottom of the vertical is connectedto the ground radial with a clip lead so it can be taken out of the circuitwhen I want the monopole to be omnidirectional. The array turned out to be veryeffective in changing the pattern of the monopole and there is a markedimprovement on signals from the northeast both in North America and from Europeas realized in the recent 160 meter contest. The best measure, though, turned out to be courtesy of WD5COV who isabout 125 miles southwest from me.  Hissignal is usually about 40 over S9 when he has his 4 square pointed myway.  After installing the parasiticelement his signal dropped to about 20 over S9 on peaks.  Unfortunately the antenna has not improved mynoise problems but that is another story.

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