20 meter HF ham radio dipole antenna

Dipole Antenna KD3Y
The dipole antenna is the most widely used type of antenna for high frequencies and in physics theory, is the simplest form of antenna.  A one-half wavelength dipole antenna commonly consists of two quarter-wavelength pieces of copper wire, called "legs", placed end to end, then trimmed to the resonant center frequency of the desired band.  The feedline is then connected to each leg.  In a dipole antenna design, the highest voltage is found at the center end of each dipole leg whilst the lowest voltage is found at each furthest end of the dipole leg.  Thus, the highest resistance is found at each furthest end of each dipole leg whilst the lowest resistance is found at the center of the dipole leg.  The transmitter cycles alternating current through each leg of the dipole, and each leg is always the inverse polarity of it's counterpart.  Any type of conductive metal wire can be used to make the legs of a dipole; copper being the best conductor whilst steel being the most durable conductor.  Copper is a soft metal and tends to stretch, causing the dipole leg to snap in high winds, yet steel is a poorer conductor and is susceptible to corrosion.  So, oftentimes, copper-coated steel wire is preferred as a trade off between superior conductivity VS strength.

Heinrich Hertz first demonstrated the concept of the dipole antenna in 1887, and Gugliemo Marconi perfected the design.  Thru his design, Marconi was able to design dipole antennae in the early 20th century to achieve long-distance radio communications from ships at sea.   At that time, telegraph was the main means of long-distance communication, but it required stations to be connected by wires.  Many lighthouses and certainly ships at sea couldn't be connected together by a cable, so Marconni set out in 1897 to invent a wireless communication system.  By 1910, Marconi had equipped most passenger ships operating in the Atlantic with his wireless radio, and provided Morse operators to passenger ships operating between Europe and North America for a fee.  Under Marconi's license agreement, wireless operators were employees of the Marconi Company, operated under Marconi Company rules, and were considered officers aboard their ships. Their duties included sending important operational and safety messages to other vessels in the area, and relaying passenger messages to coastal stations for a fee.  The new technology was something of a fashionable novelty, and first-class passengers enjoyed being able to send messages to friends and family hundreds of miles away on shore.  Marconi's wireless transmitted about 300 miles during the day and about 800 - 1,000 miles at night due to the refraction of the radio waves in the Earth's ionosphere.  Titanic was outfitted with the best wireless equipment Marconi had to offer, and her multi-wire "T" dipole antenna was over 150 feet in height, ran nearly 400 feet in length between Titanics fore and aft smokestacks, and was made of #18 B&S uninsulated silicon bronze wire.

I built my 20-meter dipole HF antenna from 14 gauge stranded copper wire.  I made friction end insulators from 3/4" schedule 40 PVC pipe and the center yoke from a "T" electrical fitting with a weatherproof access cover.  I trimmed my 20 meter dipole to 14.280 MHz and achieved a 1.5 SWR.

I have talked to other hams in Salerno Italy, Germany, Chicago, Florida, Germany, Japan, and Boston with my home made 20 meter dipole HF antenna.

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