how does an antenna physically works?
103677
the phenomenon is called electgromagnetic induction. The incoming signal induces electric current of variying strength in the antenna which is used by the receiving device.
856622
Glad to see you're thinking, but this is an easily answered question.  \n\nTake for example a magnet.  Regardless of what is in front of your magnet it will still attract an object to a distance equal to its strength.\n\nex:\n\n.....(|)<<<< <[]<<<<<<<[]          \n\n......^..............^...... ......^\nMagnet......Metal..... ..Metal\n.................Object.... Object\n\nThe magnet is going to exert force on both of the objects without interference from first object.  \n\nBased on your definition of propagate...come to your own conclusion...that is the joy of thinking...we all have our own thoughts.
1097196
You have to move the antenna around while slowly turning the tuning dial to get really good reception.  The radio should have a switch that alternates from AM to FM.
259738
Google images tab is the best way. \nyou might want to look here too\nhttp://en.wikipedia.org/wiki/Antenna_(biology)
481454
ADF's detect an electric field and a magnetic field which are perpendicular in space and their amplitudes vary sinusoidally with time. The magnetic field induces a voltage into the windings of the ADF loop antenna. By measuring the phase difference between the windings the ADF is able to determine the direction of the beacon. \n\nPutting beacons around the house and using ADF to navigate turns out to be expensive and inefficient as GPS and proximity sensors are available and work better.
1024727
shape r for some reasons if u can understand then u  read these\n\nFrequency versus length\nDipoles that are much smaller than the wavelength of the signal are called Hertzian, short, or infinitesimal dipoles. These have a very low radiation resistance and a high reactance, making them inefficient, but they are often the only available antennas at very long wavelengths. Dipoles whose length is half the wavelength of the signal are called half-wave dipoles, and are more efficient. In general radio engineering, the term dipole usually means a half-wave dipole (center-fed).\n\nA half-wave dipole is cut to length according to the formula l = 468 / f, where l is the length in feet and f is the center frequency in MHz [1]. The metric formula is l = 142.65 / f, where l is the length in meters. The length of the dipole antenna is about 95% of half a wavelength at the speed of light in free space. This is because the velocity of propagation of electromagnetic waves in wire is slower than that in free space\n\nSet-top TV antenna\nThe most common dipole antenna is the "rabbit ears" type used with televisions. While theoretically the dipole elements should be along the same line, "rabbit ears" are adjustable in length and angle. Larger dipoles are sometimes hung in a V shape with the center near the radio equipment on the ground or the ends on the ground with the center supported. Shorter dipoles can be hung vertically.\n\n\nFolded dipole\nAnother common place one can see dipoles is as antennas for the FM band - these are folded dipoles. The tips of the antenna are folded back until they almost meet at the feedpoint, such that the antenna comprises one entire wavelength. The main advantage of this arrangement is an improved bandwidth over a standard half-wave dipole.\n\n\nShortwave antenna\nDipoles for longer wavelengths are made from solid or stranded wire. Portable dipole antennas are made from wire that can be rolled up when not in use. Ropes with weights on the ends can be thrown over supports such as tree branches and then used to hoist up the antenna. The center and the connecting cable can be hoisted up with the ends on the ground or the ends hoisted up between two supports in a V shape. While permanent antennas can be trimmed to the proper length, it is helpful if portable antennas are adjustable to allow for local conditions when moved. One easy way is to fold the ends of the elements to form loops and use adjustable clamps. The loops can then be used as attachment points.\n\nIt is important to fit a good insulator at the ends of the dipole, as failure to do so can lead to a flashover if the dipole is used with a transmitter. One cheap insulator is the plastic carrier that holds a pack of beer cans together. This beer can insulator is an example of how a household object can be used in place of an expensive object sold for use as an item of radio equipment. Other objects that can be used as insulators include buttons from old clothing.
95368
No problem!  A parabola is a parabola.  The distance from the parabola to the focus is the same no matter the wavelength.  Your 3 dB beam width and antenna gain will, however, vary with wavelength.  The antenna gain (EIRP) is given as\n\nGmax = nu(pi D f/c)^2\n\nwhere nu is your antenna efficiency (0.5-0.8 is typical), D is the diameter of the antenna, f is your frequency, and c is the speed of light, 3*10^8 m/s\n\nYour 3 dB width (an approximation) is given by:\n\nTheta = 70(lambda/D) = 70(c/fD)\n\nlambda = wavelength, D = diameter of your dish, c = speed of light, f=frequency\n\nIn order to make this work, you will need multiple feeds, typically appropriate length dipoles tuned for each band, at the focus of the parabola.\n\nMake sense?
141854
Ok, so some people should not be posting answers here.\n\nRadio waves do not pass through all objects.  It depends on two things, the dielectric constant of the object and thus the frequency of the radio wave.\n\nFor example, if you have a conductor (copper, or aluminum or iron) it will reflect the radio waves.  The waves will not pass through the object.\n\nFor most objects that are not conductors, when you pass from free space (air) to a solid like concrete, a portion of the radio wave will reflect off the surface (a small portion), some of the energy of the wave will be absorbed by the object, but the rest of the wave will pass through. \n\nDepending on the thickness of the material and the frequency of the signal, and the dielectric constant of the material, sometimes radio waves will not pass through the object.  As the signal travels through the material, it will continuously lose active power (heat) and reactive power (stored energy like in a capacitor).\n\nIf you were to compare the signal strength before it hits the wall, and the signal strength after it leaves the other side of the wall, some energy would have been lost.
932508
Microwave antenna's with ice shields.
438842
Like light rays radio waves are reflected refracted and diffracted and absorbed by materials. At certain angle of reflection radio waves are also polarized.\n\nSince it is an E.M wave it travels in vacuum or air with velocity C.\n\nThey are reflected by metals, but absorbed by many substances like wall. The absorption depends upon the thickness of the material.Usually the thicknes of a wall is such as to absorb radio waves. \n\nBecause of long wavelength it can bend across obstacles, and even small cleavage in a wall can fill a room with radio waves.
1006427
RADAR is an acronym that stands for RAdio Detection And Ranging.  It works by emitting a very short pulse of radio frequency energy.  This energy travels out from the Radar antenna until it strikes the surface of a radiowave refective object.  A portion of this energy is returned to the antenna, where it is detected.  Since radio waves move at the speed of light (~186,000 miles per second), this means that it travels one mile every 6.7 microseconds (6.7 millionth of a second).  This might seem like a very fast time, but is still easily measureable.  So if the pulses refection returns in 13.4 microseconds, that means the object is one mile away. (6.7 out + 6.7 back).  The radar equipment is designed to know what direction the antenna is pointed when it send out its pulse, so it can then show on its display exactly where the target is located in both direction (azimuth) and distance (range).\n  As for how it effects the body,  Radar energy is a form of microwave energy, same as the stuff in your microwave oven.  Microwave energy has the effect of heating different types of molecules, such as water, sugar and fats.  This heating effect can damage the body just as if you were inside a microwave oven.  However, as said before, the actual energy pulse is very short.  Remember, after the pulse is produced, you have to wait for the pulse to return before you can send out the next one.  So most radars have an average power (power over time) of not much more than a 60W lightbulb.  Also remember that, except for a few special types, radar antennas are constantly spinning around, so that the amount of energy that passes by any one place is very small.  You can be as close as 5 feet away from most navigation radars without any fear of injury.  (just don't stay there for too long).
986380
It will align with whatever magnetic field it is closest to or align itself on a piece of metal. If it isn't close to either of these, it will point in any random direction.
239908
TRANSMITTER ,RECEIVER, ANTENNA COAX SWITCH, COAXIAL CABLE FOR ANTENNA, ANTENNA, ANTENNA STRUCTURE. 2 EACH. MAKE A SYSTEM.\n\nOR\n\nTRANSCEIVER , COAX , ANTENNA, ANTENNA SUPPORT! 2 EACH. MAKE A SYSTEM.\n\n\nTRANSCEIVER COULD BE FM, OR AM. AIRCRAFT USE AM FOR PLANE TO PLANE AND PLANE TO GROUND. POLICE , FIRE, UTILITIES AND MOST LAND MOBILE USE NARROW BAND FM. CB IS AM MODULATION. THE NEW CB IN HIGHBAND IS 900 MHZ FM THIS IS WHAT YOU CAN GET AT WALMART IN THE LITTLE WALKI-TALKIES! WITH A 6 MILE RANGE!\n\nA SYSTEM IS SYMPLY A SENDING STATION AND A RECEIVING STATION. IT CAN BE VERY COMPLEX OR AS SIMPLE AS A SET OF WALKIE TALKIES. A SYSTEM IS A FUNCTIONAL DEFINITON FOR SOMETHING THAT WORKS!\n\nA SYSTEM COULD REFER TO A SYSTEM THAT YOU USE AROUND YOUR HOME TO KEEP IN COMMUNICATION WITH YOUR FAMILY! OR IT COULD BE A SYSTEM THAT A BUSINESS USES TO STAY IN TOUCH WITH ITS EMPLOYEES! A SYSTEM IS JUST A FUNCTIONAL DEFINITION OF A OPERATIONAL "SYSTEM". IT IS THAT SIMPLE!\n\nHOPE THAT CLEARS THAT UP FOR YOUR!\n\n\nDO ME A FAVOR AND VOTE TO BREAK THE TIE ON YOUR QUESTION ON RADAR AS A DISTANCE FINDER IF YOU HAVENT CHOSEN A ANSWER YET SO THAT ONE OF US WILL GET OUR POINTS !\n\n\nTHANK YOU!!! \n\n\nSEE THE FIRST QUESTION!\nYOU ASKED THIS TWICE\n\nAPS\n\n\nhttp://answers.yahoo.com/my/profile;_ylt=AkNRDPHU4.dwE9DX6LQDRNgezKIX?show=AA10836052\nPOGI N POGI 88 YOU HAVE A PROBLEM YOU ARE NOT SELECTING THE ANSWERS!  YOU ASK QUESTIONS BUT DO NOT SELECT THE ANSWER! BECAUSE I AM SELECTING THE ANSWERS SO FAR FOR YOU ON YOUR QUESTIONS! ME! GET WITH THE PROGRAM! YOU ARE RUNNING OUT OF POINTS! SELECT THE BEST ANSWER YOURSELF! DO NOT LET IT HAVE TO GO TO VOTE! DO YOUR DUTY!  YOU HAVE NO POINTS THIS WEEK!  GET WITH THE PROGRAM!  IF YOU ASK QUESTIONS SELECT THE ANSWER OR DO NOT ASK!\n\nTHERE ARE WAYS OF TELLING!
273546
It depends on the type of system.  You have point to point, which is direct communications betweent two radio stations.  You have repeater operation, which allows two or more radio stations to communicate with each other through a third system, which relays transmissions over a single frequency pair.\n\nYou have conventional repeaters, or trunked repeaters.  Conventional systems work as mentioned above.  Trunked systems utilize several frequencies, controlled by computer.  Frequency pairs are assigned on a first come basis, and are rotated among all the radios on a system.\n\nRadio is not transmitted through a satellite, unless it *is* satellite radio.  Radio systems operate via a ground antenna system.
126863
The RF waves emanating from an antenna are generated by the movement of electrical charges in the antenna. Electromagnetic waves can be characterized by a wavelength and a frequency. The wavelength is the distance covered by one complete cycle of the electromagnetic wave, while the frequency is the number of electromagnetic waves passing a given point in one second. The frequency of an RF signal is usually expressed in terms of a unit called the "hertz" (abbreviated "Hz"). One Hz equals one cycle per second. One megahertz ("MHz") equals one million cycles per second.
854507
HowStuffWorks.com is a resourceful website for these type of questions.\n\nhttp://home.howstuffworks.com/microwave.htm
874938
I assume you mean a half-wave dipole antenna.  The formula is L = 468/f, or f = 468/L, where f is the frequency in megahertz and L is the length in feet.  This formula takes into consideration "end effects," ie, deviation of antenna performance from the theoretical ideal, due to charge accumulation at the antenna tips.  For a folded dipole, or other similar antenna that doesn't have open ends, it's f = 492/L.