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.
N7DF
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|