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Radio fact sheet
First, the basic concepts of broadcasting
Broadcast by radio or wire transmission of voice, images with multiple functions of modern communication tools.
1, broadcast the benefits:
(1) the broadcast variety: from the geographical perspective, there are local, domestic and foreign programs; from the content point of view, there is practical information, weather forecasts, traffic information, stock market, pop music, foreign language teaching, science and technology knowledge .
(2) audience participation, for example, can demand the song is basically free.
(3) without charge, as long as the radio on the line, buy a radio in general the price of only a few dozen to a hundred or so.
(4) receive information easily, the current radio size is small, although not at home, its furnishings position, but it was made ??into MP3, cell phone, pen in, got into people’s pockets, carry easy, go where you can listen to.
(5) earthquakes and other natural disasters, the lines were damaged, there is no fixed telephone and mobile communications, no electricity will not watch TV, this time, radio became the victims of the only channel with the outside world, they both can understand the outside world through radio rescue information can also be broadcast to find lost contact with their loved ones.
2, broadcast Category:
View from the means of communication, broadcasting two broad categories:
① radio waves transmitted through the program, known as the radio; ② by wire transfer programs, as cable broadcasts.
From the media perspective, radio can also be divided into two categories:
① only the transmission of voice, called voice broadcasting, referred to as the broadcast; ② transmission of voice, images, known as the television broadcast.
From the broadcast signal modulation modes: FM (FM) and AM radio (AM) broadcast two.
From the use of the radio band is divided into: long wave (LW), medium wave (MW), short wave (SW) and FM.
Currently, the long wave, medium wave and short wave radio are amplitude modulation mode used; FM radio using the FM band.
3, the principles of broadcasting
People’s voices in the air can spread dozens, or hundreds of meters, how can we spread the sound very far away go? Radio is an effective means.
The speed of propagation of radio waves similar to light, and propagation is very slow decay, their energy consumption is very small in the dissemination process, the waveform is essentially no change over time, we are using radio waves to transmit signals of these two features of . Specific process can be simply stated as: in the radio signal into corresponding audio (low frequency) signals, added to the radio waves, this process is modulated, so that radio waves to the speed of 300,000 km per second to directions sent to every corner of the world; with radio listeners receive the audio signal containing the high-frequency radio waves, after a series circuit of the processing to restore the sound out of this process is the demodulation. So that we listen to the radio, from radio programs.
Second, what is the AM / FM?
We use the radio to listen to radio, and often heard the radio DJ broadcast, for example: FM88.1 Chongqing music radio, FM96.8/AM1314 Chongqing news broadcasts and so on. So what is it FM and AM? What are the characteristics of their respective?
1, in fact, refers to the AM and FM radio science on two different modulation methods.
AM: Amplitude Modulation is called amplitude modulation. The so-called amplitude modulation, is the audio signal and the amplitude of the high-frequency carrier signal at the same time sent to the modulator, the high amplitude low frequency signal amplitude with the magnitude of change.
FM is Frequency Modulation, known as FM. The so-called FM, is the audio signal and high-frequency carrier signal with equal amplitude into the modulator, the frequency of high-frequency signals with low signal frequency changes.
Radio Transmitter for AM and FM signals in two ways, so as to receive the broadcast AM and FM radio are also divided, but the vast majority of dual-use of AM and FM.
2, AM / FM features
(1) AM: The current long wave, medium wave and short wave radio are used in AM mode. In the long, medium and short wave radio waves are vulnerable to the spread of day and night, seasons, movement of sunspots and other factors, could easily lead to interference with the signal amplitude changes, so not as good as FM reception quality is good, but spreads far and is widely used for medium and long-distance radio.
(2) FM: change is usually because of interference signal amplitude, without affecting the signal frequency; So FM radio waves and strong anti-interference than AM radio, low noise, wide band, good sound quality, can transmit high-fidelity stereo programs which are widely used all over the city, county, radio, broadcast within the city.
Third, the basic concepts of radio
Said earlier FM88.1 AM1314, 88.1 and 1314, what the article in the inside it? This is the radio frequency used by radio, which had to start from the simple concept of radio.
1, What is radio?
Radio wave is an electromagnetic wave. Its production, according to Maxwell’s electromagnetic theory, it can be described: If the pass on to the wire current leads four weeks to produce changes in the magnetic field. In the area around the magnetic field will produce changes in the electric field; the change of the electric field but also produce changes in the distant region of the magnetic field … … so back and forth to continue, changes in the electric and magnetic field changes constantly handover transformation, by near and far to spread out in space to form the radio waves.
Second, what is the frequency, wavelength, band
Invisible radio waves to electrical, magnetic energy exists, although the eye can not see, but we can still describe the characteristics of the radio wave laws, but in the process, must use some proper nouns, such as frequency, wavelength, band, etc.
(1) frequency, radio transmitters produce radio waves is the driving force, where the first current to swing back and forth very quickly, that is, oscillation, amplification and processing through the transmitter, then transported to the tower’s antenna, where That is where the actual produce radio waves. See Figure 1 below, which curve represents the relationship between intensity and time, along the antenna, radio waves generated by the flow of electronic, assuming the curve to the left is the starting point, we can see the curve gradually increased from zero, then back to to zero, which means that the current in the antenna, from one end toward the other end of the generated radio waves and when the current ran back from the other side, they had a zero baseline below the curve, this is a cycle back and forth, and continue to Repeat to move back and forth movement; baseline curve above and below the maximum value, known as the amplitude; repeated changes in the number of times per second is called frequency (F).
The basic unit of frequency is hertz, symbol Hz to represent. In radio technology, the need to use much larger unit: kilohertz (kHz), megahertz (MHz), gigahertz (GHz). The relationship between them is:
1kHz = 1000Hz 1GHz = 1000MHz = 1000000kHz
Another important parameter is the electromagnetic wavelength, is the wave propagation at a distance from the oscillation period, the Greek letter λ said. In meters (m), the smaller is the millimeter and micron. Because the speed of radio waves is constant (300000000m / sec), the decision long and short wavelengths is the natural frequency.
For example: in front of said AM1314, frequency of 1314kHz, its wavelength is:
Wavelength (m) = velocity (m) ÷ frequency (Hz)
= 300000000m ÷ 1314000Hz ≈ 228m
Habits and convenient method of calculation is converted to frequency units of megahertz (MHz), with 300 units in MHz divided by the number of frequencies, the wavelength can be obtained, the unit is still rice.
To facilitate the management and recognition, the International Telecommunication Union to a certain wavelength range of a radio frequency block designated according to their wavelength, known as the band’s call.
MW (Medium Wave abbreviation), meaning Poland. However, due to short wavelength than the wavelength shorter than the long wave, medium wave, it said. MW broadcasting using amplitude modulation due to (AM) approach, most of the FM, AM radio, two-band scale is marked as FM & AM, so unknowingly, MW and AM between the equal sign. So our daily said refers to the medium-wave AM band (MW), such as Chongqing, news stations reported the AM1314 kHz. AM broadcast frequency range 531-1620kHz, the Americas now has expanded to 1710kHz, 10kHz spacing in addition to the radio in the region, the rest of 9kHz.
LW (Long Wave abbreviation), lower than the AM MW frequency 150KHz-284KHz spectrum between this period, its wavelength of about 1000 to 2000 meters, and MW compared to the 200-600 meters obviously “long “more, so called long-wave radio interval 9kHz. At present, only few countries in Europe LW radio.
SW (Short Wave abbreviation), is a simple short term, but short is how the name come from? The wavelength, the wave (MW) between 200-600 meters, while the short wavelength is between 10 to 120 meters, compared with some really short, so called short-wave. Short-wave radio frequency range is usually between 2.3 ~ 26.1MHz radio interval 5kHz. International Telecommunication Union (ITU) regulations, paragraph UHF radio frequency for civilian use, the other short-wave frequencies for other civilian or military communications, but there is still a small number of radio frequency meter band outside.
What is the use of the FM radio band? We are used to refer to FM to FM radio in general, its frequency range in addition to Japan, 76-90MHz, the other countries for 87.5-108MHz. In fact belong to FM band FM radio frequency.
The general collection (recorded) sound machine in terms of, FM, MW, LW band is used to provide you listen to country radio, while the SW band is mainly for you to listen to domestic / international long-distance broadcasts.
3, radio wave propagation characteristics:
(1) medium wave and long wave characteristics:
①, MW of transmission mainly by ground wave, only a small part in the form of sky-wave propagation. Radio waves across the conductor, the conductor will be induced current, and thus part of the energy loss. This makes the phenomenon of wave energy is called the weak absorption of radio waves. The earth is a conductor, a strong absorption of medium wave, so the form of ground wave propagation of wave propagation in the near (about two to three hundred kilometers), as a province, city broadcasting. Has a similar long-wave and medium wave propagation characteristics.
②, during the day as sunlight, the ionospheric density, resulting in sky-wave propagation in the form of a small part of Poland into the ionosphere to be strongly absorbed, difficult to return to the ground, combined with the ground wave propagation of wave propagation in the form of not very far, So far during the day is difficult to receive AM radio station, to the night, the atmosphere is no longer affected by sunlight, so the thin ionosphere, the density becomes smaller, electrical conductivity variation of the radio wave absorption is also greatly reduced. Then, through the medium wave skywave channels can be transmitted to the far (hundreds to thousands km) areas. So the night before the AM radio for more, there are neighboring provinces, and even received in Taiwan, Japan, South Korea, the radio station.
(2) short-wave features:
Mainly in the form of HF sky-wave propagation, which is 200 by 400 kilometers above the Earth’s ionosphere, a high reflection or refracted back and forth after the return to the ground, transmission distance can reach thousands of kilometers, often as intercontinental transoceanic international broadcasting use, but the vast territory like Russia, China, Indonesia, extensive use of short wave broadcasting as a domestic.
Ionospheric absorption of short-wave than less so during the day and at night can receive short-wave radio, but because the ionosphere will be the season, day and night and the solar activity cycle, when the strong waves caused by weak, unstable, when there is listening a voice suddenly suddenly small phenomenon, which is called signal “fading.”
(3) FM radio features:
FM radio signal is the direct wave propagation, also known as line of sight transmission. Signal coverage in general is about 100 km radius, but in the summer, due to special weather conditions, sometimes transmit to hundreds of thousands of kilometers to, which is broadcast fans said FM-DX phenomenon.
Radio Selection Guide articles
First, radio Category:
1, divided by band: AM (medium wave), FM / AM two band; FM stereo / AM two band; FM / MW / SW 3-5 band; FM / MW / SW 8-12 band; FM stereo / MW / SW 8-12 band; TV audio (VHF-L, or VHF-H) and other radio;
2, according to the technical characteristics of the circuit can be divided into: conventional superheterodyne (IC / transistor circuit); with digital electronic clock and clock-controlled function (LCD-type / LED type / fluorescent-type display); analog tuner / digital display of frequency and Time (not stored frequency); frequency synthesizer type (PLL) digital tuning (digital, can be stored frequency); uses double-conversion technology (high sensitivity and excellent selectivity); high sensitivity shortwave / single sideband (SSB) receiver (professional HAM RADIO).
3, according to the shape can be divided into: mini, pocket, portable, desktop, toy … …;
4, by using the power supply can be divided into: One to VII ordinary battery, rechargeable battery, AC power, solar power, spring or Dynamo (such as Germany, born Green 88/138) … …
5, according to the tuning can be divided into: analog tuner and digital tuner two.
Analog tuner: radio stations by adjusting the knob to change the radio’s internal variable capacitor to achieve. Traditional Analog, digital display frequency tuning knob (not stored frequency) of the machine are.
Digital Tuning: Tuning is by means within the microcomputer chip to achieve, now mostly PLL tuning system (PLL). This radio can receive the frequency accuracy and stability shows that there is no frequency drift, and can store the radio frequency, as well as regular open, off time setting, use the more convenient.
Second, determine the type you want
To listen to the radio, you have to have a good performance of the radio, how to choose a suitable radio it? Three main aspects to consider: 1, use 2, price 3, listen to the environment
1, determine the purpose:
(1) In general, most users usually only listen to local radio stations, buy universal AM / FM two band radio on it (such as R208, R212T, 202T, DE307).
(2) love music, the sound quality demanding users, like FM radio, they need to carry out radio users should purchase a portable or pocket-type high-grade stereo FM radio (such as the German students R101, R829B, Degen’s DE102, DE303, DE103), the pros and cons with quality headphones, stereo radio sound effects on the reproduction a great impact.
(3), often at home, if you listen close, I suggest you buy a size bigger the desktop (such as the German students R308, BCL3000, Robinson PR2100, etc.). Or high-grade mini-component systems, such a large volume machine, good sound quality, can also play CD & DVD, and some also with the deck. Panasonic, Philips, Aiwa, backgammon, Redden, Panda and other brands.
(4) in order to listen to distant radio stations at home and abroad, you need to buy the multi-band radio with shortwave. Such as: universal virtuous health cards R909, R908, R1210, R911, Degen’s DE301, DE304, DE312, etc. (the price of tens of dollars or so). Better preclude the use of double-conversion technology, shortwave reception relatively clear, some strong anti-jamming, frequency stability better, such as the German students R9710, 9700DX, Degen’s DE1107 (with electronic clock and timer switch) so, the price of 150 or so.
(5) If you are a radio fan, like to listen to several radio stations, you need time off function, high quality requirements of the radio, I suggest you buy a digital radio tuner tone, high frequency stability, both display frequency , can store frequency, very easy to use. Such as the German students PL200, 230,450,600, Degen’s DE1102, 1103,1105, these types of models the price of around $ 300, can store hundreds of frequencies. These models are a little electricity to charge some batteries are generally only listen for a twenty or thirty hours, you can use the adapter or rechargeable batteries. German high-grade raw radio S2000, sensitivity, selectivity is very high, can also receive civil aviation navigation and communication and SSB communications, but the price is higher. If you only listen to at home is recommended to select size larger portable or desktop radios, electrical properties relative to a bit better, you can use 1 AC or battery, its benefits are loud, good sound quality.
(6) If you want to listen to TV sound, select the radio with TV sound, should be noted that some so-called TV sound only 3 to 5 radio channels. Recommended to choose the German students R1212A, R1012, R305, R9700, CR100, CR1000, may be received from 1 to 12 channels. (Note: TV audio signal depending on whether there is around the launch, depending on the propagation characteristics similar to the FM radio.)
2, the price factors:
Determine the type of radio is right for you, they still consider the price. Radio on the market a wide variety of brands and varieties, the price of similar products vary different, the main factors affecting the price of the brand, quality and service is good or bad. Price difference between similar models made of 5% -20%, while imports and domestic models are comparable difference of 100% -300%. Note: The price difference between different functions of the machine is also larger, but still more functions, the more expensive the better the price! Or applied should be selected functional performance, reliable quality, good service, reasonably priced products.
Domestic good brand is: TECSUN Desheng, DEGEN Degen, music letters. International brand: SONY, Grundig GRUNDIG (its products are now producing more than the mainland), Sangean SANGEAN and so on.
3, listen to the environment:
Also note that your location. City FM radio stations more available to buy FM stereo radio; and away from the city mountain, rural, less often, or not receive FM radio, you buy a radio with AM or shortwave.
Third, choose the radio
Buy a good performance of the radio, listening to your radio is a great advantage.
1, the radio’s main performance indicators:
(1), frequency range, commonly referred to as bandwidth, FM should be 87.5 or 88-108MHz, if a student friends on campus to receive the FM radio, the FM bandwidth should buy the 70-108MHz, MW is 530-1620kHz, and most of the bandwidth of the radio SW models vary according to differences in general listen to international radio ,5.8-18 .0 MHz on it, if you want to listen to more radio stations need a wider point ,3.2-22.0 MHz can handle almost all of the shortwave radio, digital tuning radio SW Most have a wide frequency range.
(2), sensitivity: the higher the sensitivity to receive weak signals of great help. The smaller the number of its mark, indicating higher sensitivity. FM is generally up to 5 microvolts (uV), MW up to 5 mV / m (mV / m), SW to 20-30 microvolts (uV) pretty good.
(3), selective: selective good radio, listen to some of the relative will be clear, less susceptible to interference from adjacent radio broadcast. Single-signal selectivity at least not less than 20 db (db), the larger the number the better.
(4), output power: that is a popular speaker playback volume level. General use twenty-three 5, a small portable radio battery is rated output of 250 milliwatts (mW) so, for the average person listening is possible. Some desktop machines can reach 1-2 watts or more power, and high and low tone adjustment function.
2, purchase Notes:
In addition to these major technical indicators, but also pay attention to the radio housing to robust, uniform burr knot tight seam surface appearance clear font. The volume to maximum, there should be no noticeable distortion, that is not broken voice of the phenomenon. The radio has better high and low tone adjustment function, and some in the MW / SW bands have band width adjustment, can take into account the reception and good sound quality. Other cases, Analog and digital sub-tuned to explain.
A, Analog Radio:
1 tuning knob is turned to feel smooth, moderately elastic, the pointer in the middle of the scale of the tightness on both sides and to be consistent, do not have a clear friction and sound card, astringent feeling.
2 indicate the frequency scale must be accurate, you can use to test their own familiar radio, digital tuning machines can also be compared.
3 Listen for some time, to see whether the treadmill (that is, frequency drift), especially short wave band.
4 for the segment is divided by UHF multi-band shortwave radio, pay attention to see how much meter band. It is noteworthy that some will be divided into several meter band short wave of 22m this machine does not meter band, especially a few years ago the model, such as the German Health R909.
B, digital tuning Radio:
1, the buttons to be flexible, touch intensity should be moderate, even, a sense of touch to crisp.
2, tuning step, FM has 0.1/0.05/0.01MHz, and the FM demanding alternative 0.05/0.01, and more precise adjustment of frequency, the reception better. For the MW / SW, the best choice for a 1KHz tuning step of the model, so that when the adjacent station interference, you can adjust the listening to the radio frequency to avoid interference. Often listen to shortwave listener, you can choose a double-conversion circuit models, such anti-mirror machine (false signals) interfere with the ability of the model is better than the normal circuit, noise should be smaller in general, the first IF higher than the machine receives the highest frequency than the first IF frequency range of the receiving machine, anti-interference ability to mirror some more.
3 for the number of short-wave machine tune, the best to have a direct function of input frequency, can you know the radio frequency directly using the numeric buttons to play in, very convenient, or transfer station is more cumbersome. Currently the number of tone with the tuning knob tuning the radio to radio stations is more convenient.
4 storage, there are hundreds to thousands of radio frequency memory, large memory capacity for often listen to more radio listeners, it is practical.
Radio listening skills articles
First, how to get radio time and frequency table?
1, can be seen on local radio and television reported that the local radio broadcast schedules and frequencies.
2, the Chinese Radio Network www.cnr.cn, view CCTV and some local stations broadcasting time and frequency.
3, if you listen to international radio stations abroad, such programs are mostly broadcast in the morning and evening. The beginning or end of the show they will broadcast frequency, or you can provide according to the radio address, e-mail them a letter, request program schedule.
4, radio enthusiasts in the forum, you can query to many domestic and international radio broadcast frequencies. www.leowood.net
Second, why hear the good, there will be a sudden shrill noise?
TV, computers, motors, hair dryer, lamp, lamp dimmer, cell phones, chargers, etc., will interfere with reception, but the quality is good or bad with these devices and the different degree of interference distance is different as far as possible away from the listening device on or off . If you are using the AC when murmur hinder listen, if still can not rule out the elimination of the above reasons, please do use the battery to prevent electricity caused interference. Between long-term use of funds to spend a larger battery, I suggest you use high quality rechargeable batteries, have super, Sanyo, Sony and other brands, but to guard against counterfeit products, save money but also a contribution to environmental protection, because good quality rechargeable batteries can be recharged 500 times normal or more.
Third, how to properly adjust your radio?
Skyscrapers or reinforced concrete interior, the waves have some shielding effect, the signal will weaken. This situation can consider installing an outdoor antenna.
1, FM radio, you can change the length or direction of the rod antenna to improve reception. For a little remote areas to receive FM radio, you can use a wire whip antenna will be used in outdoor TV antenna connected electronic amplification, and some regional cable network has spread FM radio, you can try to connect to cable TV jack.
[Click] another window to open the picture …
2, the vast majority of radio is by the machine’s magnetic antenna to receive AM signals, this antenna is highly directional, with the bar magnet when the signal direction perpendicular to the direction of receiving the strongest signal, so when receiving AM rotation direction of the radio. If the signal is weak interior, the old software can use a wire, a coil was wrapped around the radio like 10 laps on the shell (note: different winding direction may be different due to the radio), received a window open at the other end.
3, shortwave listening:
a, the trial provided all radio frequencies, choose the best listening.
b, open or close the window in place to listen to, the rod antenna all the way out and keep with the desktop vertically.
c, adjust the signal attenuation switch, the signal is weak when appropriated for DX, the signal is strong appropriated Local.
d, if the radio signal is weak or strong room for shielding radio waves, you can set up an external antenna. Method as shown below:
1, in the walls of windows, insulated jacket with a common wire, a nail fixed.
2, the other end hanging down to their own windows, pull into the room and fixed.
3, the end of the wire connecting the radio, connection method:
A, insert the radio antenna jack. B. If the radio is very small, but also the end of the antenna coil was wrapped around the rod-shaped antenna, telescopic antenna and maintain insulation.
If you want to receive weak shortwave signal, then you can stand in a place outdoors, 10 meters or more antennas.
1, if your radio is relatively small, the antenna will not do too long, the length of the signal, but contains appropriate. Otherwise the signal is too strong, but the effect is not good.
2, the antenna should pay attention to lightning protection, lightning weather do not use an external antenna.
3, the body must have an external antenna cable insulation jacket, which can prevent static damage to on the radio.
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