The MFJ-17754 is a two band, 40- and 20-Meter center-fed dipole
antenna capable of handling 1500 watts. Its total length is 42 feet.
Each side of the dipole is broken up by a coil that presents a high
impedance at 20 meters and acts as a loading coil on 40 meters, allowing
the antenna to resonate on 40 meters even though it is physically
shorter than a half-wavelength (approximately 65 feet at 7.1 MHz).
Because this antenna acts as a dipole on both bands its impedance is in
the vicinity of 50 to 70 ohms, permitting it to be fed with coaxial
cable. The use of a current balun between the coaxial feedline and the
antenna is highly recommended, to help prevent stray RF from traveling
down the coaxial cable’s outer shield. This is easily accomplished with
an MFJ-915 RF Isolator and a “double male” coaxial connector. |