Radio systems use EMF for wireless communication.There are many radio systems, such as AM and FM radio, as well as television. A typical system is made up of transmitters and receivers. Both the transmitter and receiver have antennae that either launch (transmit) or collect (receive) radio waves. The transmitter antenna can be compared to the light bulb that emits light produced by electricity (transmitter). One can also think of the receiving antenna as an eye that collects light emitted by the light bulb, while our optical nervous pathway in the brain can be compared to the radio receiver. [This can't possibly be right according to their own statements. The eye can't possibly see anything, because light is non-ionising (as they've just told us in the Introduction) and therefore can't break chemical bonds, and therefore (by implication), can't cause biological changes to human cells or tissues] The antenna of a radio transmitter emits electromagnetic fields at specific allocated frequencies, which contain specific information such as voice or pictures. The information is encoded in radio waves in various ways. For example, in the AM (amplitude modulation) radio, the amplitude of the signal follows changes in the sound strength and pitch, whereas in the FM (frequency modulation) radio, the sound signal changes the frequency of radio waves. More complex ways of encoding information are used in TV and mobile phones, but they basically involve changes in amplitude and/or frequency of the waves. The receiver does not produce any radio waves, but is designed to receive and translate radio signals of a specific type. Thus, a radio receiver does not produce electromagnetic waves, and it needs to be tuned to listen to different stations. Some radio systems contain both a receiver and a transmitter in one device. The best known example is a mobile phone. In telecommunications, the transmission of information via RF signals is accomplished by applying some form of modulation to a carrier wave. Basic modulation schemes modify the carrier wave's amplitude, frequency or phase. Complex modulation schemes are used to minimize transmission errors and increase bandwidth in telecommunications.62 Digital systems transmit information in bursts, thereby introducing an amplitude modulation component onto the carrier. Analog phone systems generally use narrow band frequency modulation, which causes phase variations in the carrier with very little amplitude change. Electromagnetic radiation with a high frequency carrier wave (e.g., radiowave) and an extremely low frequency (ELF) modulation is considered amplitude modulated (e.g. TDMA mobile phone systems). The modulation can also be pulsed where the carrier wave is switched on and off very rapidly in the rate of about 100 pulses per second (e.g., GSM mobile phone systems), while continuous wave (cw) radiation is generated essentially at a single frequency (e.g., analog mobile phone systems). Different biological effects have been reported for pulsed and continuous wave radiation.66 [1.They've managed to get confused about frequency modulation (FM) and amplitude modulation (AM) when all the Canadian AMPS phones are FM.
2. Then they've confused AM with TDMA, when one is a modulation system and the other is a shared-access technique. TDMA does not use amplitude modulated, it uses phase modulation.
3. Then they've apparently failed to realise that GSM mobiles use TDMA access technology. 4. Then they apparently believe GSM pulses at 100 Hz (pulses per second) rather than 217 Hz.
These are not trivial mistakes, and certainly such mistakes don't inspire confidence that the authors know what they are talking about. The only sentence they actually got right is the last. "Different biological effects have been reported for pulsed and continuous
wave radiation" -- by highly reputable scientist.] Radio waves have frequencies ranging from about one million hertz or one megahertz (MHz) for AM radio to hundreds of millions for some TV transmitters and several billions for mobile phones. Table 1 illustrates the frequency band, the typical power output, and the required power in maximum direction for various radio transmitters.
Radio waves propagate in air in straight lines with speed of light. Their power density (strength) decreases rapidly with distance. Radio waves can be radiated by antennae either in all directions with the same strength, or in a beam of a certain width, as illustrated in Figure 2. If the antenna is directional, its power is greater in direction of the beam, and typically 100 to 1000 times less outside of the beam. A good analogy to this is the beam of light coming from a flashlight. For directional antennas, Table 1 shows the enhancement of the radiated "power in maximum direction". Antenna beam width can be limited in both elevation (vertical plane) and azimuth (horizontal plane). Figure 2. Antenna radiation patterns (A) omnidirectional, and (B) directional, limited beam width. 
Antennas of base stations for mobile phones typically have beam widths that are about seven degrees. They are very narrow in elevation (i.e. vertical), and about 120 degrees, or one third of a circle, in azimuth (i.e. horizontal). There are usually three (sectorial) beams in azimuth. The beam is tilted a few degrees in the vertical direction, so it intersects the ground some considerable distance away from the antenna tower. Each base station covers a limited radius away from the tower. Beyond that radius, the power density is too small for a mobile (portable) phone to work. The phone is automatically switched to a closer base station. The total power output of a typical mobile phone base station depends
on the type of antenna(e), the number of analog and digital channels
that operate at a given time and at their maximum strength, and the
antenna gain which gives the signals direction and strength. |
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