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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 ...
Parallel-wire line (the generic sense of twin lead) is supplied in several different sizes, with values of 600 Ω, 500 Ω (ladder line), 450 Ω, 350 Ω (window line), 300 Ω (window line, ribbon cable), and 75 Ω (ribbon cable) characteristic impedance.
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.
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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 ...
The Bottom Line. Red wine is one of the most enjoyed alcoholic beverages around the world. And it’s known to be high in polyphenols—a type of antioxidants that may lessen your risk of heart ...
Enjoy a classic game of Hearts and watch out for the Queen of Spades!
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