When you start looking at antennas longer than about a/3, you sometimes run into an interesting marketing gambit. Antenna manufacturers tend to market their long Yagis based on element count, with the boom length buried in the specifications sheet. In fact, boom length is arguably the most critical parameter in long boom Yagi design. For any given boom length, there is an optimum design (including an optimum number of elements) that will provide the gain shown in Fig 19-10. with an antenna on a given boom length with more elements; however, that doesn't mean that this design has more value than one with less elements — in fact, since most antenna installations are designed to with- stand a certain level of wind force, having more directors (and hence more wind-surface area) may well be a disadvantage. Watch this if you are considering buying an antenna array.