![]() Field strength measurements showed the copper coil produced a. Photo 4 shows an example of two different coils that have been used and evaluated for the 40 meter antenna. The efficiency of a SVA is reduced primarily due to loss in the coil assembly required to make the antenna resonant. This high Q antenna has a 2:1 VSWR bandwidth of 50 KHz and return loss is greater than 25 dB, or a VSWR of 1.12:1 at the resonance frequency. A Ruthroff designed high efficient 4:1 coaxial toroid transformer, Photo 3, is installed at the base of the antenna to produce an impedance of 50 ohms at the feed line connection. The base impedance of 12 ohms was achieved by positioning the inductor, used to resonant the antenna on 7.2 MHz, 30 inches below the top hat. The vertical element is 10 feet high and a 5 foot diameter capacitive top hat is used to increase the base impedance. Photo 2 is an example of the SVA for 40 meters. This is a huge advantage because there is no need to insert networks or other matching devices to compensate for the mutual couple impedance change. Short vertical elements spaced one-half wavelength apart, avoid any mutual coupling that would change the self resonance impedance of the elements. Photo 1 is the initial two element array with the additional third element. Adding a third element the bidirectional main lobe and the null can be positioned in increments of 30 degrees. ![]() ![]() This array was limited because the bidirectional radiation pattern could only be turned in increments of 90 degrees by changing the phase (0 or 180 degrees) of the RF current between the elements. The initial 40 meter phased array consists of two 10 foot high elements spaced one-half wave length apart. ![]() I have used short vertical antennas (SVA) since the mid 1970's, and have used the SVA's for short vertical phase arrays (SVPA) for several years with positive results. ![]()
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