Force 12 Sigma-280 Magnum Assembly Instructions Manual

Sigma-280 Magnum
2 element 80/75 Meter Yagi Antenna
FREQUENCY COVERAGE: CW and Phone segments, each approximately 100 kHz 2:1 VSWR
Force 12, Inc.
P.O. Box 1293 Bridgeport, TX 76426
Technical Support and Order Line:1 940 683 8371 FAX 1.940 683 8378
Thank you for selecting the Force 12 Sigma-280 Magnum 2 element Yagi for 80/75 meters. Released in
the summer of 2003, the Sigma-280 Magnum is another step up in the finest 80/75 meter production Yagis.
It is the product of about 9 years of development and the Sigma design is the new era in efficient antenna
design for both horizontal and vertical antennas. Thanks to the members of Team Vertical and their years
of competitive operating that eventually led to this design. Sigma-280 Magnum is composed of a pair of
Sigma-180 Magnum dipole elements. One is the driver and the other is the reflector. Other than their
tuning, they are physically identical. The function of each element is determined by the tuning of each one
and that the coax feed line goes to the driver. This manual describes building each dipole element, the
attachment to the boom of both and how to tune the antenna. Yagis for 80/75 meters are tuned much
differently than one would expect. The old theory that the reflector is tuned 3-5% lower in frequency does
not hold. The reflector is actually tuned approximately 0.7% lower.
The Sigma-280 Magnum covers several segments of the 80/75 meter band with the 2-relay external switch
box. The antenna is composed of two elements. Each has T-bar capacitive loading about 24' out on each
side, plus large diameter, Hi-Q coils on each side of the feed point, providing the highest efficiency of any
shortened antenna to date. The antenna is designed to present a low profile and withstand winds in excess
of 90 mph.
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