Please help me with this.... Why a radio station can be broadcast to a whole city from a single antenna, whereas a mobile phone system needs a network of basestations??? Thanks,,,
A radio station can send the same signal to all. Sure, you have several radio stations, but that is nothing against the number of mobile phone calls in a city. You have to make smaller cells to handle that number. In less populated areas, the station density can be lower. Another difference: radio stations send at longer wavelengths, those are less sensitive to local obstacles.
The power a radio station is able to broadcast is often measured in kilowatts. (50,000 watt AM superstations, anyone?) Radio stations can broadcast to more than a whole city. AM Superstations can cover half the continental US, if the conditions are right. The power in a mobile phone handset? Maybe a few watts tops, which limits the range of the signal. Because of the short range of the mobile signal, a chain of signal towers is required to pick up the signal, feed it into the phone network, and then broadcast to the receiver phone. When traveling and you lose your cell phone signal, it's because there is a big obstacle in the way, like a mountain, or you are no longer close to a cell tower.
What is the context for your question? Is this a question you were asked in school? What grade level are you in school now?
TBH I'm not sure on the radiated power from a radio station, however mobile vehicle radios have a maximum radiated power of 50 watts, only if licensed, Canadian FCC regulations has a baseline radiated power of 25 watts. For the portable 2 way radios the radiated power is 5 to 10 watts. Lower frequencies can travel farther, such as AM radio, however their penetration is lower. Higher frequency ranges has better penetration. Some cell phones have a frequency range of 900 MHz to 1.2 ghz if memory serves me correct.
Thanks all,,, just I would like to mention the main difference between them. For the radio station, because all receivers receive the same information, hence it is limited by propagation. But in cellular system, each user wants different information, so it is limited by bandwidth. So the cellular system needs several transmitters using the same frequency, one of which is closer to the receiver than the others..
A list of the 50,000 watt stations in the US: http://en.wikipedia.org/wiki/List_of_50_kW_AM_radio_stations_in_the_United_States 50 kW is currently the highest broadcast output authorized by the FCC.
A broadcast station transmits at high power. The phone tower not only transmits, but it must also receive, and it needs to receive relatively weak signals---those from nearby handheld phones.
