DSFO144-12
The DSFO144-12 is a high performance yagi antenna design. The original design was perfected by Steve Powlishen, K1FO, who spent hundreds of hours optimizing yagi designs on a high powered Hewlett Packard computer. He started with some computer optimized designs of Tom Kirby, W1EJ, (SK) who was using computer software developed at Ohio State University. W1EJ had came up with many excellent VHF long yagi designs. The finished K1FO designs were carefully checked out in the real world by K1FO to ensure accuracy of the design effort. His efforts have produced an exceptional design with maximum gain very close to the maximum amount possible, while keeping sidelobes, (particularly those of the H-plane) at a very low level. The net result is broad bandwidth, wide beamwidth, and clean lobe structure. Clean H-plane patterns translate to efficient stacking with maximum possible gain and manageable array sidelobes. The design has been published in many printings of the ARRL Handbook. Of course, any adapted design should be checked on a real antenna range to verify that specific materials sizes and architectures have not skewed the results away from the chosen design frequency. All Directive Systems antennas are verified for proper performance on antenna ranges with very good swept measurement equipment. The DSFO144-12 is no exception. Some performance curves have been provided below on these pages.
DSFO144-12 YAGI
To evaluate the bandwidth, click here. To look at return loss (VSWR), click here.
The DSFO144-12 specifications are listed here.
The DSFO144-12 yagi employs a traditional modified T match and half wave balun to match your 50 ohm feedline to the driven element. The T match provides a great method for achieving proper match along with exemplary decoupling of the feedline from unwanted antenna currents. Poor decoupling efforts can reduce gain by large amounts. If any power flows on the outside of the coaxial cable, or along the antenna boom, gain or efficiency suffers drastically. Poor decoupling will show up as varying VSWR as the feedline is handled. Deep response nulls within the passband of the yagi are a tip off as well. Any skewing of the main lobe off the boresite heading indicates out of control rf currents caused by poor (or no) decoupling. A sample close up of a typical T match is shown here. The actual antenna is a 432 yagi and it presents a more compact photo that shows maximum detail.
SAMPLE DRIVEN ELEMENT T MATCH DETAIL
The DSFO144-12 computer modeled patterns are here:
The DSFO144-12 is a natural for installation as an array of antennas for higher gain. The three piece boom is about as long as is possible with no additional boom braces required. It will stand up to heavy ice loads. Antennas with braces or support wires are more prone to failures in bad weather. Long boom antennas simply generate huge amounts of strain and stress in ice and high winds. When the DSFO144-12 is installed in an array, wind loading from extraneous support struts and wire supports is not a problem. The clean H plane pattern allows wide spacings with resulting great patterns with low noise pickup. You can look at a few pictures below of some representative arrays from around the country.
N3NGE FN20 KA1ZE FN01
Why not to have long yagis with braces (Don't try this at home kids!)
