The basic geometry of a Yagi-Uda antenna is shown below in Figure 1. Geometry of Yagi-Uda antenna. The Yagi antenna consists of a single 'feed' or 'driven' element, typically a dipole or a folded dipole antenna. This is the only member of the above structure that is actually excited a source voltage or current applied.
History of radio Rough plot of Earth's atmospheric transmittance or opacity to various wavelengths of electromagnetic radiationincluding radio waves. Radio waves were first predicted by mathematical work done in by Scottish mathematical physicist James Clerk Maxwell. His mathematical theory, now called Maxwell's equationsdescribed light waves and radio waves as waves of electromagnetism that travel in space, radiated by a charged particle as it undergoes acceleration.
InHeinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory,  showing that they exhibited the same wave properties as light: Radio waves, originally called "Hertzian waves",  were first used for communication in the mid s by Guglielmo Marconiwho developed the first practical radio transmitters and receivers.
The modern term "radio wave" replaced the original name "Hertzian wave" around Speed, wavelength, and frequency[ edit ] Animated diagram of a half-wave dipole antenna receiving a radio wave. The antenna consists of two metal rods connected to a receiver R.
Since the length of the antenna is one half the wavelength of the wave, the oscillating field induces standing waves of voltage V, represented by red band and current in the rods.
The oscillating currents black arrows flow down the transmission line and through the receiver represented by the resistance R. Radio waves in vacuum travel at the speed of light. Air is thin enough that in the Earth's atmosphere radio waves travel very close to the speed of light.
A 1 megahertz radio signal has a wavelength of Radio propagation The study of radio propagationhow radio waves move in free space and over the surface of the Earth, is vitally important in the design of practical radio systems. Radio waves passing through different environments experience reflectionrefractionpolarizationdiffractionand absorption.
Different frequencies experience different combinations of these phenomena in the Earth's atmosphere, making certain radio bands more useful for specific purposes than others. Practical radio systems mainly use three different techniques of radio propagation to communicate: This refers to radio waves that travel in a straight line from the transmitting antenna to the receiving antenna.
It does not necessarily require a cleared sight path; at lower frequencies radio waves can pass through buildings, foliage and other obstructions.
This is the method used by cell phonesFM and television broadcasting and radar. By using dish antennas to transmit beams of microwaves, point-to-point microwave relay links transmit telephone and television signals over long distances up to the visual horizon.
Ground stations can communicate with satellites and spacecraft billions of miles from Earth. Radio waves can reach points beyond the line-of-sight by diffraction and reflection.
|Medium Wave Circle - Antenna advice||The loop is erected horizontal to the earth The feed arrangement for operating the loop as a vertical antenna Full Wave Loop Antenna by WH2T I have personally used a meter band Horizontal Full Wave Loop antenna with very good success. I worked all 50 states and several countries with Watts using the antenna on the meter band.|
|2 Meter Amateur Radio J-Pole Antenna||Included is my experience-driven rationale for what is in this kit and what is not, and why. I have used the types of parts and techniques in this kit for decades and it supports almost any kind of field radio installation from HF through 6 and 2 meters.|
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|Antenna And Wave Propagation - heartoftexashop.com heartoftexashop.com heartoftexashop.com - Google Books||In this chapter, let us go through different interesting topics such as the properties of radio waves, the propagation of radio waves and their types. Radio Waves Radio waves are easy to generate and are widely used for both indoor and outdoor communications because of their ability to pass through buildings and travel long distances.|
Radio waves also reflect from surfaces such as walls, floors, ceilings, vehicles and the ground. These propagation methods occur in short range radio communication systems such as cell phonescordless phoneswalkie-talkiesand wireless networks.
A drawback of this mode is multipath propagationin which radio waves travel from the transmitting to the receiving antenna via multiple paths. The waves interfereoften causing fading and other reception problems.
This allows mediumwave and longwave broadcasting stations to have coverage areas beyond the horizon, out to hundreds of miles. As the frequency drops, the losses decrease and the achievable range increases.
Military very low frequency VLF and extremely low frequency ELF communication systems can communicate over most of the Earth, and with submarines hundreds of feet underwater.
At medium wave and shortwave wavelengths, radio waves reflect off conductive layers of charged particles ions in a part of the atmosphere called the ionosphere.
So radio waves directed at an angle into the sky can return to Earth beyond the horizon; this is called "skip" or "skywave" propagation.Integrated Publishing, Inc.
Google +. Wave propagation is any of the ways in which waves travel.. With respect to the direction of the oscillation relative to the propagation direction, we can distinguish between longitudinal wave and transverse waves.. For electromagnetic waves, propagation may occur in a vacuum as well as in a material medium.
Other wave types cannot propagate through a vacuum and need a transmission . Fractal Antenna Systems custom designs, manufactures and licenses the world's most compact and powerful antennas for commercial and military applications.
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The ARRL Antenna Book is a practical introduction to antenna design. For a book this thick, it's strange to call it an introduction, but it is as it covers everything from safety, through antenna performance, to antenna design and modeling.
Your first antenna – the half-wave dipole. Many hams’ first choice of antenna is a half-wave dipole. But don’t be misled – just because they are easy to make doesn’t mean they don’t work well.