[TowerTalk] Re: 40 meter 3 Element Yagi

[Frank Donovan]

Jim,

The first YO file below is for my existing 3 element 40M Yagi.  The second
file is for the same antenna with a fourth element added to significantly
improve the VSWR bandwidth of the antenna per a design originally 
developed by K3LR.  I plan to implement the 4 element Yagi this year.  

The antenna is built on a 48 foot boom consisting of two pieces of 24 ft
x 3"od x 0.188" wall thickness 6061T6 aluminum tubing.  The elements are
insulated from the boom, mounted on 12" x 12" x 1" Type LE phenolic
plates.  

The elements use .058" wall 6061T6 aluminum tubing.  The center
24 feet of each element uses many fully telescoped pieces of 6061T6
aluminum tubing for greatly increased strength.  For example, the longest 
element uses a total wall thickness of 0.290" near the center.  The
detailed design of the elements is available as an NI6W YS (Yagi Stress)
file.

73
Frank
W3LPL
donovanf@sgate.com

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W3LPL 3 Element 40 Meter Yagi (as Built)
Height 2280.000
7.000 7.100 7.300 7.100 MHz
3 elements, inches
            2.0000    1.8750    1.7500    1.6250    1.5000    1.3750    1.2500    1.1250    1.0000 
  0.0000   72.0000  121.5000   16.5000   16.5000   17.0000   17.5000   18.0000   18.0000  134.0000 
258.0000   72.0000  121.5000   16.5000   16.5000   17.0000   17.5000   18.0000   18.0000  110.0000 
564.0000   72.0000   96.0000   15.0000   15.5000   16.0000   16.0000   16.5000   17.0000  125.0000 

Use the H key to set the elevation angle to 10
degrees.  Use the M and Tab keys to enter the
following T-match parameters:
Rod Diameter   0.5"
Rod Spacing     10"
Rod Length     144"
Lead Length      6"
Series Cap   99999 pf
Feed Z         200 ohms
Experience indicates that the driven must be 
lengthened to 125 inches, the length that 
produces a modelled impedance of +j20 at 7.1 MHz

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W3LPL Wideband 4 Element 40M Yagi (construction planned in 1997)
Height 2280.000
7.000 7.100 7.300 7.100 MHz
4 elements, inches
            2.0000    1.8750    1.7500    1.6250    1.5000    1.3750    1.2500    1.1250    1.0000 
  0.0000   72.0000  121.5000   16.5000   16.5000   17.0000   17.5000   18.0000   18.0000  134.0000 
234.7897   72.0000  121.5000   16.5000   16.5000   17.0000   17.5000   18.0000   18.0000  120.0000 
317.9102   72.0000  121.5000   15.0000   15.5000   16.0000   16.0000   16.5000   17.0000  117.0000 
564.0000   72.0000   96.0000   15.0000   15.5000   16.0000   16.0000   16.5000   17.0000  125.0000 

This design illustrates how a 4th element radically
improves the bandwidth of a 40M Yagi (thanx K3LR !)
Use the H key to set the elevation angle to 10
degrees.  Use the M and Tab keys to enter the
following T-match parameters: 
Rod Diameter  0.5" 
Rod Spacing    10" 
Rod Length    144" 
Lead Length     6"
Series Cap  99999 pf 
Feed Z        200 ohms 
Experience indicates that the driven element tip
must be lengthened to 134 inches, the length that
produces a modelled impedance of +j20 at 7.15 MHz.


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