QEX

people can't mount a 40 meter antenna far enough away from other objects to eliminate detuning effects. See for yourself how bad this is with a 2 meter mobile station and an SWR meter— then scale things up dimensionally by a factor of 20. Thus, for proper performance, low-frequency antennas often need to be tuned in-place. When they're moved, retuning is often required.

Most 6 meter Yagis are horizontally polarized and cover only the SSB/CW portion of the band. Building for horizontal polarization is much simpler with small Yagis, because interaction with vertical supports is minimized. While it might be nice to cover the entire band, the typical sacrifice in antenna performance hasn't justified the work involved in coming up with a clever design. At least I haven't seen anyone publish such a design.

These days the electrical design of antennas is easy. There are plenty of Yagi designs and computer modeling programs out there. I picked this design out of Lawson's Yagi Antenna Design because it has good gain and pattern for just four elements.1 I wanted few elements for portable work—more elements mean more assembly/disassembly time. That's a big factor when you are surrounded by black flies and other obnoxious insects. An extra element or two does give you a bit more design flexibility. You can often get the beam to work well over a wider bandwidth with more elements, while keeping the boom length constant. Extra bandwidth

1 Notes appear on page 57

helps the antenna to work well despite the effects of rain, though few Yagis work well when covered with ice. You don't get more gain by adding more elements, however, maximum gain is pretty much a function ofboom length. This is why W5UN's 24-foot-boom Yagi for 2 meter EME has just 11 elements. They just aren't needed for this particular application.2

According to Yagi Analyzer, the simple program that comes with The ARRL Antenna Book,3 the antenna has 10.6 dBi of free-space gain with the unwanted lobes suppressed by 20 dB—a reasonably clean pattern. I like to use dBi because it is relatively unambiguous. DBd measurements are problematic because some people just subtract 2.15 dB from the isotropic-

Photo 1—Driven element of the Yagi.

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