Why do electromagnetic signals i.e. FM radio and AM radio lose strength over distance?
403407
There are several reasons why, I'll list some of them:\n\n- For any given power of wave transmitted, regardless of the frequency: a radio wave will lose power the further it propogates from the transmitter source because of the square distance law (the further away from a point source, the square root of the power is received). I forget the exact way to word it, but that's one reason.\n- Atmospheric absorbtion: the atmosphere both aids in the propogation of the radio waves (the ionosphere, tropospheric bending), but it also absorbs a portion of the wave. It happens.\n\nOne of the things to keep in mind when talking about radio waves is frequency. The general rule is: the lower the frequency, the more bendable it is. At night, you can listen to AM radio stations from around the world, if you have a sharp enough receiver. During the day, because the sun's rays are interacting with our atmosphere more, exciting the ionosphere, AM propogation is cut down severely. During the Super Bowl, when I was in my car in Pennsylvania, I listened to the broadcasts on AM coming from Detroit, MI and Windsor, Ontario (approx. 600 miles away). As an amateur radio operator, I've talked to people thousands of miles away based on the bending of radio waves either directly around the earth (groundwave) or by having them "bounce" or refract in the ionosphere above the earth (skywaves). In fact, one of the "cool" things about AM radio stations is that they have 2 different antenna setups: 1 for the daytime, because the signals travel one certain way (mostly groundwave), and another setup for the nighttime, to prevent interference with other stations further away that are on the same frequency (mostly skywave). Listen in to one of your local AM stations around sunset and you should hear the automatic switch between the setups; the nighttime pattern should sound less strong, a lil warbly even.\n\nWhen you start talking about the frequencies of FM radio, however, that's not the case. They do not bounce off the ionosphere (except in extreme circumstances), and so are limited to how far they can travel via groundwave. Under certain circumstances, atmospheric ducting can conduct FM-frequency radio waves further than normal, but due to the nature of an FM radio wave as compared to an AM radio wave, it's not an appreciable distance.\n\nOne of the coolest things I've done as an amateur radio operator is use a mode called "moonbounce". Quite simply, a large antenna array is pointed at the moon (usually 8-10 antennas on a frequency higher than FM commercial radio) and you transmit. Nothing is cooler than hearing your voice come back to you 3 seconds after you transmit (1-1/2 seconds to the moon, and 1-1/2 seconds back). Amateurs all over the world use this mode of operation to talk to each other. It really works!!\n\nAs for SETI, instead of transmitting, there are massive antenna farms set up around the world to listen in to space. The primary frequencies they listen to are around 1420MHz, because this is the primary harmonic frequency of hydrogen, which everyone knows is the most abundant material in the universe. They also listen to different multiples, or harmonics of this frequency, as well as tuning up and down the dial around those frequencies to compensate for Doppler shift. It makes more sense to listen than to transmit, because if there is intelligent life out there, and they are space-faring, you would think that they would've been broadcasting a lot longer than we here on Earth would (the first radio signal that had any chance of escaping our solar system in a readable form wasn't transmitted until the 1920s!).\n\nAny more radio questions, msg them to me; I've been a licensed radio amateur for 11 years and I'll try to answer as much as I can for you!
715907
Electromagnetic waves don't need medium to travel.\n\nLike light, radio too, is an elctromagnetic wave, so it can travel through vacuum.
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.
1004300
Different reasons -- \n\n1.  Frequency separation.  Radio stations operate on different channels (frequencies) than CB radios for example.\n\n2.  Different locations.  You can operate on the same frequencies if the transmitters are located far enough away from each other.  Look how many "Channel 3" TV stations there are.  They're far enough away from each other so they don't interfere.\n\n3.  Different modulation.  FM and AM are types of modulation.  In the case of radio, they're also on different spectrums, but you could have the same frequency modulated differently and have minimal interference.\n\n4.  Digital transmission.  You can transmit information digitally over the airwaves and "multiplex" it such that it doesn't interfere with other transmissions (cell phones for example).
524846
B'coz wavelength decides the power gain that transmitting antenna should have .\n& distance that can be covered by signal also depends on wavelength.
56370
they cause electromagnetic stroms
650858
sometimes they are used for radio antennas
328292
Yes, the radio is also going to be traveling at the speed of sound because it is in the car or whatever you are in. Therefore the radio is stationary relative to you, so it makes no difference how fast you are going. If you were going away from the radio you would not be able to hear it.
682558
It is impossible to give the simple answer for which you seem to be searching.\n\nThere are many frequencies which could be used to cover that distance.\n\nI recommend you read about radio communication in general and about h.f., v.h.f. and u.h.f. communications in particular.
279538
In general, a transmitted signal can be described as s=A*cos(omega + phi).  In AM modulation, you change the amplitude "A".  In FM, you modify the fundamental frequency, omega.  In PM, you modify the phase, phi.\n\nPhase Modulation is heavily used in digital communications.  Modems, satellite TV, GPS, and Wireless LANs (802.11a/b/g) all use variants of binary and quadrature phase shift keying.
300474
I'll picture it for you...years ago when all the radios were AM Amplitude Modulation...when you drove under high voltage power-lines..you would hear static...with FM Frequency Modulation this will not happen..Higher Frequency.\n\nI hope this helped
143763
a signal emmited in the band of the 2 GHz.
568450
Overhead power-lines have a high voltage AC current flowing through them, so create a radiating magnetic field for some distance all around the wires.  When this radiated (moving, because the electricity in the cables is changing direction 60 times a second) passes through the aerial on your radio, it is likely to be at some of the same wavelengths/frequencies as something you are trying to receive deliberatly, so you get "the buzz".\n\nCheck this website out for more:
28438
AM/FM Amplitude Modulation / Frequency Modulation
442249
Generally, AM carrier waves have much longer wavelengths than FM carrier waves. AM waves can bend around obstacles like mountains and buildings better than FM waves and can travel greater distances before the signal fades. AM waves are used in aerial navigation although more modern methods (GPS and Very High Frequencies) are replacing them.
946504
Intensity varies as the square of the distance.\nThat should help
522363
you can use a fm modulator