Inverted-vee dipole Antenna

The inverted-vee dipole is a half-wavelength antenna fed in the center like a dipole.By the rigorous definition, the inverted-vee is merely a variation on the dipoletheme. But in this form of antenna (Fig. 6-7), the center is elevated as high as possi-ble from the earth’s surface, but the ends droop to very close to the surface. Angle acan be almost anything convenient, provided that a> 90 degrees; typically, most in-verted-vee antennas use an angle of about 120 degrees. Although essentially a com-pensation antenna for use when the dipole is not practical, many operators believethat it is essentially a better performer on 40 and 80 m in cases where the dipole can-not be mounted at a half-wavelength (64 ft or so).By sloping the antenna elements down from the horizontal to an angle (as shownin Fig. 6-7), the resonant frequency is effectively lowered. Thus, the antenna will

 need to be shorter for any given frequency than a dipole. There is no absolutely rig-orous equation for calculation of the overall length of the antenna elements. Al-though the concept of “absolute” length does not hold for regular dipoles, it is evenless viable for the inverted-vee. There is, however, a rule of thumb that can be fol-lowed for a starting point: Make the antenna about 6 percent shorter than a dipolefor the same frequency. The initial cut of the antenna element lengths (each quarter wavelength) is

 After this length is determined, the actual length is found from the same cut-and-try method used to tune the dipole in the previous section.Bending the elements downward also changes the feedpoint impedance of theantenna and narrows its bandwidth. Thus, some adjustment in these departments isin order. You might want to use an impedance matching scheme at the feedpoint, oran antenna tuner at the transmitter.