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Basic Antennas Understanding Practical Antennas and Design by Joel R. Hallas | PDF Free Download.
for something so simple to check out, and often so simple to make, an antenna is remarkably difficult for many people to understand.
That's unfortunate because for many radio systems the antenna is one of the most important elements, one that can make the difference between a successful and an unsuccessful system. Perhaps an analogy from The ARRLAnrenna Book will help.
Me familiar with sound systems. Whether represented by your home stereo or by an airport public address, sound systems have one thing in common.
The system's last stop on its way to your ears is a transducer, a device that transforms energy from one form to another, in this case - a loudspeaker.
The loudspeaker transforms an electrical signal that the amplifier delivers into energy in an acoustic wave that can propagate through the air to your ears.
A radio transmitter acts the lite the same way, except that its amplifier produces energy at a higher frequency than the sound you can hear, and the transducer is an antenna that transforms the high-frequency electrical energy into an electromagnetic wave.
This wave can propagate through the air (or space) for long distances. For some reason, perhaps because of our familiarity with audio system s or because you can actually hear the results in your ears. it seems easier to grasp the concept of the generation and propagation of acoustic waves than it is to understand the generation and transmission of radio waves.
The audio transmitter analogy can be continued in the receiving direction. A microphone is just another transducer that transforms acoustic waves containing speech or music into weak electrical signal s that can be amplified and processed.
Similarly, a receiving antenna captures weak electromagnetic waves and transform s them into electrical signals that can be processed in a receiver.
Fig 1-1 shows a system or block diagram of a sound system with transducers (loudspeaker Arul microphone) at each end. Many of the phenomena that act upon acoustic wave",alsn occur with electromagnetic waves.
It is not an accident that the 1I parabolic reflector radar antenna looks very much like a parabolic eavesdropping microphone, or that sonar and radar operator in the same fashion. Sonarrelies on acoustic waves propagating through the water to find and reflect back from underwater objects, such as submarines or schools of fish.
Similarly, radar send s out electromagnetic waves through space, listening for signals reflected hack from objects such as aircraft. space vehicles or weather fronts. 1 ~ 1-2 shows simplified system diagrams of radar and sonar systems.
While we're mentally picturing antennas. perhaps an even better analogy than acoustic waves is to compare electromagnetic waves of light to those of radio signals. Light waves propagate through space using me the same mechan ism s and at the same speed as radio wa...es.
Similar parabolic shapes can reflect and focus both light and radio waves. Light needs a polished mirror as a reflector. such as the mirrored reflector in your flashlight or car headlight I will sometimes dra w on yo ur appreciation of light reflection as I discuss some types of antennas.
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