Why dont two radio signals at different frequencies interfere?How does a signal actualy travel in air?

Question

Basically i am confused and i am curious to know how exactly a signal is transmitted in the air,i want to visualize it.I will be thankful if u can provide any link?

Answer 1

The answers you received so far targeted a non-tech audience. Let's try a semi-tech (qualitative only, no math) one from a retired engineer to see how serious things could get.

In a vacuum any two RF signals of any frequencies, same or different, interfere one another fully. In any other media, in addition, any two signals intermodulate one another.

If the two carrier RF signals have different frequencies that are spaced further apart than both of the modulating signals' base-band bandwidths, the two can be separated using an available technology such as by frequency filtering using a band pass filter, by heterodyning using a mixer, or by a DSP Fourier transform. Only in this "fully recoverable" sense, the two signals of different frequencies are said to not interfere one another.

When the bandwidths of the base band modulating signals are wider than the spacing of the two RF carriers, a process call "aliasing" occurs which causes non-recoverable interference even though the two carriers are of different frequencies.

On the contrary, two RF signals of the same frequency can still NOT interfere one another. For example, a circularly polarized wave has two RF waves of the same frequency with their electric (and magnetic) fields perpendicular to on another in space and 90 degree off in time (phase). They geometrically (think vectors) add to one another to make the total electric field appear to rotate in a circle as the wave propagates. A material call bi-refringent can separate the two component waves. As the demand to share the RF bandwidth keeps growing you will soon see wireless networks use a new technology call spatial diversity using MIMO (multiple input multiple output) antennas: Two perpendicular channels concurrently use the same RF frequency by turning the antennae dipoles 90 degree from one another.

One last comment, two RF of different frequencies can also intermodulate to generate a wide range of other frequencies which are linear (multiplied) and linear-affine (multiplied and add/subtract) combinations of one another significantly to a degree as high as 9th. (Degree here means how many times the frequencies are multiply itself or multiply one another). This intermodulation is the reason we are required to turn off cell phones in an airplane so that they do not interfere with telemetry and traffic controllers' radios even though every device uses a different frequency. A worldwide huge multi-billion USD RF sub-industry is focusing on getting rid of the third-order intermodulations between frequencies, so two different frequencies DO indeed interfere very costly.

Too confusing?

Cheers!

Answer 2

A receiver for an AM, FM, CB radio or even a cell phone is designed to seek a certain wavelength of a radio signal. Radio waves like light, X-rays, microwaves, gamma waves, etc. all work on the principal of frequency and wavelength, where the frequency is inversely proportional to the wavelength. Radio waves are normally measured in gigahertz and megahertz and a hertz is the measure of how many times a wave oscillates in a second; therefore the higher the number of hertz, the more cycles that occur each second and the shorter that the resulting length of each wave is. This relationship holds true for all types of energy in the electromagnetic spectrum. Provided that two signals are not competing at the same wavelength, than no distortion will occur. The Federal Communications Commission regulates the bandwidth assigned to radio stations, cell phone companies, CB bands and even military communications to avoid and limit issues. The garbled signal that you sometimes hear comes from two stations being picked up at the same time or a lack of signal strength. All a radio does is receive radio signals, decipher the specific frequency you want, and then coverts that signal to electrical impulses which drive radio speakers which in turn create sound that you hear.

Answer 3

Radio waves travel like light. Light is actually a frequency range that is visible to us. Some antennas transmit like a light bulb, round. Some antennas focus the radio waves, like a flashlight. Interference does not occur on different frequencies, it's like the way sound doesn't interfere with light, because they are on different frequencies. Cellphones have filters, like a car radio, where it will only pick up the channel that it is told to pick up.

Answer 4

All different signals have to pass filters. The filters are sellected to be only one frequency. As a result, the other frequencies are get out.

Answer 5

Radio waves don't interfere with each other for the same reason that sounds waves or water waves don't interfere with each other. With sound waves, two people can talk at the same time without one voice affecting other. With water waves, two waves can pass right through each other without any net effect.

Answer 6

Radio and Sound waves will not interfer with each other in a linear medium as they can add and subtract with each other without losses. A non-linear medium would cause interference.

Answer 7

they are two different frequencies if they are different frequencies they wouldn't interfear with each other if they were the same frequencie they would interfear with each other (you really get the hang of this stuff after you read how cell phone jammers work)

http://electronics.howstuffworks.com/cell-phone-jammer.htm