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The J-pole antenna is an end-fed omnidirectional half-wave antenna that is matched to the feedline by a shorted quarter-wave parallel transmission line stub. [5] [1] [6] For a transmitting antenna to operate efficiently, absorbing all the power provided by its feedline, the antenna must be impedance matched to the line; it must have a resistance equal to the feedline's characteristic impedance.
With no matching unit, Varney specified 75 Ω cable be used at the junction of the ladder line and coax (not 50 Ω); the higher 75 Ω impedance makes a closer match the end of the ladder line. An earth-grounded 4:1 voltage balun may be used to connect the coax to the ladder line, and 1:1 current balun should be used between the coax and the ...
Ladder line is an older, simpler form of parallel-wire line, often called open wire line. The configuration looks like a rope ladder , hence the name. It can either be purchased already made by a cable company, or home-made ; the construction is easy, though tedious, and originally all radio amateurs made their own open wire line.
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The most widely used types of feed line are coaxial cable, twin-lead, ladder line, and at microwave frequencies, waveguide. Particularly with a transmitting antenna, the feed line is a critical component that must be adjusted to work correctly with the antenna and transmitter. Each type of transmission line has a specific characteristic impedance.
MORE: US Marshals hunt for man suspected of killing 29-year-old woman, burying body in shallow grave “Due to his Santa-antics, Langlais was transported to a local hospital out of precaution and ...
From January 2008 to May 2010, if you bought shares in companies when Robert I. MacDonnell joined the board, and sold them when he left, you would have a -30.7 percent return on your investment, compared to a -24.0 percent return from the S&P 500.
It is usually fed at its center with the feedline cable itself slanting away at a perpendicular counter-slope from the sloping antenna wire, towards a small pole or a ground anchor near the base of the mast. [e] The sloper's far end is attached by a cord to a short pole or fastened by an insulated cord to a ground anchor. It is popular because ...