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1 Economical <strong>Antenna</strong>s for LF/MF CHAPTER 12 From the Book by Robert C. Wilson, AL7KK Economical <strong>Antenna</strong>s for Low & Medium Frequencies <strong>12.0</strong> <strong>The</strong> <strong>Vertical</strong> <strong>Antenna</strong> <strong>and</strong> <strong>Some</strong> <strong>Variations</strong> 12.1 <strong>The</strong> Basic <strong>Vertical</strong> <strong>Antenna</strong>. <strong>The</strong> most basic low frequency antenna is the quarter wavelength vertical antenna. A quarter wave is practical <strong>and</strong> reasonable above about 1000 kHz. Below roughly 1000 kHz, the vertical requires considerably greater economic resources. Since this book is about economic antennas, I shall try to concentrate on antennas less than approximately 150 feet, or 50 meters, in height. <strong>The</strong> most basic tubular or lattice work quarter wave vertical is simply one half of a half wave dipole antenna. It uses the ground as a mirror to simulate the missing half of the dipole. However using the ground as a mirror requires a low resistance ground system. Low losses mean using salt-water grounds, or extensive wire grounds. Much of this has already been covered in Chapter 5. <strong>Vertical</strong> antennas tend to radiate along the surface of the earth giving the best distance coverage for the money. <strong>The</strong>re will be a notch in the lowest part of the vertical pattern of all vertical antennas. This will occur unless the ground is perfect, like a sheet of copper over the ground. <strong>The</strong> depth of this notch will greatly effect range. Because the vertical is the basic antenna from which almost all other low frequency antennas are derived I will spend a bit of time showing some details of such antennas operating between 100 <strong>and</strong> 2000 Khz. Table 12.1- 1 shows the impedances for four heights of tower, tuner parameters, <strong>and</strong> estimated range to the 70-microvolt contour using a 1000 Watt transmitter. Notice that shorter antennas at low frequencies have lower radiation resistances <strong>and</strong> consequently lower efficiency. Low efficiency means Chapter <strong>12.0</strong> ~ <strong>The</strong> <strong>Vertical</strong> <strong>Antenna</strong> <strong>and</strong> <strong>Some</strong> <strong>Variations</strong>