Original article from: Wayne Sarosi 
 Reposted by Rob Dennis,Moderator HAM_TECH,for use of the FIDO HAM_TECH echo.
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SUBJECT:  Gamma modification for better symmetry & gain
 This subject has been discussed before on the HAM echo and will be further
discussed here with more detail.
 Most gamma matching devices are mounted to the side of the driven element.
 This technique is good for matching,but does not provide good pattern.
 The symmetry of the antenna pattern is distorted to the side of the antenna
that the gamma match is located on. Several antenna brands were tested with
all brands tested showing the same result. The pattern produced by the side
mounted gamma is kidney shaped. This shaping accounts for the fact that you
can hear a signal on one side of the beam and not the other.
 The side to side ratio is not consistant. In the case of horizontal 
eams,the
gamma hangs down,wasting gain and affording a loss of signal reception that
could otherwise be used.
 What would it take to move this lost antenna gain and sensitivity into the
area of the pattern that could be utilized?  Not a whole lot in fact.
 The entire modification can be done in under a half an hour and for less 
han
a dollar. What results is that the wasted gain to the side of a vertical beam
is moved forward and the wasted gain under a horizontal beam is moved into 
he
horizontal plane forward. The average gain increase is near 1.5 dB over the
previous gain rating of the antenna. What this means is that if your antenna
produces 10 dBi it will now produce 11.5 dbi. Your Cushcraft eleven element
yagi rated at 13.2 dBi will now produce 14.7 dBi. 13 dB is equal to a gain of
20,16 dB is a gain of 40,so you can see the improvement.
 To accomplish this,you will need to remove the gamma match from the antenna.
 Remove the di-electric innards and replace with a piece of RG-8 foam
di-electric about 3-in longer.
 Pivot the tuning arm 90 degrees so that it faces the first director.
 Insert the gamma back into the tuning arm.
 Now,solder to the center pin of the coax feed point. If your coax feed point
is a threaded section,crimp or solder on the appropriate fitting,then tighten
the nut. You will need to retune the antenna at this point.
 Fairly easy?  The results are incredible.
 Increased gain,better symmetry,better side to side and front to back ratios.
 This modification has been used here for over a year. When I turn the beam 
o
the side of a signal,the results blow away any commercial beam.
 My nine element yagi can keep up with the commercial eleven element 
ntennas.
 Try it out. I'm sure you will enjoy the change.
-WS
--- GoldED 2.42.G1219
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