It said the first radio knowledge:
Radio in various emergencies play a very important role, so often use of relief on the radio, below I some basic knowledge about radio
Definition: radio is to point to in free space (including air and vacuum) of the spread of electromagnetic wave, is one of the limited frequency band, cap in 300 GHz frequency (ji hz), the lower frequency less unity, in all kinds of rf specifications, common are 3 KHz ~ 300 GHz (ITU-the international telecommunications union regulation), 9 KHz ~ 300 GHz, 10 KHz ~ 300 GHz.
Electromagnetic waves:
(1) produce: when the conductor through the rapid change of current, conductor will to the space around it launch electromagnetic waves.
(2) spread: electromagnetic wave travel don't need medium, can travel through a vacuum, also can be spread in the media. Radio communications use of electromagnetic wave that radio waves, is in a certain range of frequency electromagnetic waves.
(3) the frequency, wave length, the relations between the wave, electromagnetic waves in a vacuum in the rate of spread and the speed of light is the same, is, in the air in the rate of spread and in a vacuum in approximate. The frequency, wave length, wave the relation among the three for wave velocity = wavelength × frequency, with letters for said.
Says below some basic knowledge about radio:
It is often asked so-and-so type of radio will be how far to the problem. To tell you the truth, every time asked this question will have the feeling of difficult to explain.
In the wireless communication professional, no "distance" the technical parameters, because can affect wireless signals travel to remote factor is really too much.
Commonly used radios generally use 130-170; 403-470 two frequencies, the two frequency band is also allows individuals or units state laws used frequency range.
Usually, the two wave frequency is the spread of the straight line, and the sea is the radios of the phone calls are ideal environment, general will not have obstacles and little interference, but in fact, in the sea on the handheld only 10-20 miles or so on, it is because the earth is round, too far apart will be among the block. (so the day higher, explosive filling call distance would also more far)
Usually in the city when using, obstacles to signal transmission distance is the biggest impact factors. 5 watts of power to professional in the cities on the actual distance calls only commonly 2 ~ 5 kilometers in the range. In highland, more buildings or more of the seal of indoor, call distance will also shorter. But when a system support base station, the radio call can be up to 10 km range even a few kilometers, (if two sets are on high on the, also can achieve more than ten kilometers).
Market 0.5 W interphone, manufacturer of nominal maximum distance calls is 3 kilometers, in fact the call distance is only a theory calculation data, it was based on the transmission power, that is 0.5 W radio without obstacles, not in electromagnetic interference call the maximum distance. In actual use, because users circumstances of each are not identical, background noise is big is small, electromagnetic interference, weak or strong, so the actual conversation was less than 3 km distance generally. Many users buy when the intercom mistake that often use in the city, call distance can reach 3 kilometers, it is not likely to be! No factory are not possible to predict the use of user environment, of course, is impossible to give the actual distance calls.
So in answer to the customer about the problem of the distance (city in the straight distance), I feel that the answer is more objective: a. handheld intercom: 5 watts professional machine: 1-5 km; 2 watts hand platform: 1-3 km; 0.5 MinYongJi: 500-1000 meters. B. car radios (usually power in 25 watts around) : five to 15 km.
Another is that
In a radio communication field, is not "call distance" of the parameters. The term usually because users buy interphone are in an issue of concern, users of course think radio calls the farther the distance, the better. In fact the radio call distance by many factors influence.
The launch of the radio electromagnetic signals, the transfer of the process by building, mountains, and woods, electromagnetic field and block and interference, affect the actual call distance and quality. Electromagnetic interference especially severe cases, call a short distance sometimes can't even communication. Some careful old users find a problem, don't understand of ask me, why now call distance to catch up with the radio for many years old products? Investigate its reason is now the electromagnetic environment of than years ago worse! Radio is not very popular before, mobile phone or high-end consumer goods, electromagnetic interference is not serious, but now we all the time in the electromagnetic wave surrounded by, so inevitably lead to this phenomenon.
A comparison of easy to understand parables, we in the calm surface of the water lost a stone, splashing water will slowly spread to distant place, if we also lost a few stone, you will find that the spread of water no longer so far distance, because water wave each other mutual interference offset! By the same token, the mutual interference of electromagnetic wave will affect the radio call distance.
The experiment proved that in the urban areas, the actual radio conversation about effective distance for about 3 km, and in the suburbs may be a little bit more, for 4 kilometers). Of course, if a certain network support, such as setting the repeater, radio call distance and up to 5 kilometers above, such as the base station, even to dozens, hundreds of kilometers.
If the call distance higher demand, the usage situation the complexity of the terrain, the proposal to buy the W. (the greater the power, the farther the distance. The most power is on the 5 W!)
