This e-mail contains the YO file for the full size 3 element 40M Yagis on
48 foot booms at W3LPL, one at 190 feet and the other at 100 feet. These
antennas have been in use for 25 years with excellent success.
The design is a compromise between gain, front/back ratio and VSWR across
the entire band. A three element Yagi does not have enough variables to
allow a good compromise design covering the entire 40M band; therefore,
the design favors good f/b ratio and VSWR from 7000-7100 kHz, good gain
from 7000-7300 kHz and acceptable VSWR from 7150-7300 kHz.
K3LR has implemented a 4 element design on the same boom length that
solves the VSWR bandwidth problem of a 3 element 40M Yagi. I have not yet
added a fourth element to my 40M Yagis, but a candidate design is included
at the end of this e-mail, as a YO file. This design clearly demonstrates
the excellent VSWR performance improvement resulting from the addition of
a fourth element on the same boomlength.
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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
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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