Introduction of radio 1. The traditional pointer if it receives the kinds of tuning shortwave radio radio band dividing: single band medium-wave radio: 525 MW 525-1600 KHz frequency modulation amplitude modulated radio MW - 1600 KHz, FM/FM 87.5-108 MHz in shortwave radio * * MW / 525-1600 KHz, FM 87.5-108 MHz is only a short period of SW: 3.9-12.00 MHz (75-25 meters) (or 6.00 -- 6.00 MHz, 49, 16 meters) (or 9.00 -- 9.00 MHz, 31-19 meters) when two short wave period of SW1:2.2-7.50 MHz, SW2:7.50-23.00 MHz or SW1:5.9-9.50 MHz, SW2:9.50-18.00 MHz press meters to differentiate SW1, SW2, SW3, SW4 and SW5, SW6, SW7......... Multiband shortwave radio (each shortwave coverage of an international shortwave meters) traditional radio and tape recorder usually only one or two short wave period, but each band covers a very wide frequency range (several meters), the advantages of simple circuit, but it is difficult to ensure that covered the frequency range of each point of the frequency sensitivity and selectivity is very uniform, therefore, are often some meters to listen to is very good, some are very poor, in addition, due to cover a very wide frequency, make appear very crowded, and between different radio platform is not convenient, so some radio to attach the short-wave fine-tune knob to improve. There are some very good traditional radio short-wave circuit design, the radio has enough high sensitivity and selectivity, and production debugging and very precise, use rise very convenient also, don't interesting, at least save old in band of trouble. In addition, the traditional radio USES mostly 3-4 batteries and larger diameter of speakers, listen to it sounds very good. No wonder there are a lot of old shortwave fans still like traditional radio. 2. According to the meters to classification of multiband shortwave radio modern shortwave radio, often divided into 6-10 short wave period, each shortwave covers only a meters (please refer to the below international broadcasting meters table), for such a shortwave radio well designed, easy to guarantee the sensitivity and selectivity, and according to the meters to differentiate short wave, the gap between the radio seems to be fair kuo, receive short-wave like to listen to the mw is convenient, especially for the most intense,19,25,31 16 meters, radio advantage more prominent. Press meters to divide the short-wave radio, if insufficient, is due to the short wave period is too much, for people like different stations and often have to switch short wave period, and appear a little trouble. In addition, according to the classification to design the shortwave radio of meters, if you want to cover all short-wave frequency range, short wave light requires 13 bands, and each band to design reasonable, a lot of electronic components of the materials used, the circuit is too complex and the cost is too high. I have seen imported brand short-wave radios, FM/medium-wave/long wave/short-wave/short wave all band together, up to 15 bands, the price is nearly 1000 yuan. It is worth mentioning that in the domestic market, but also some short-wave radio, so-called 18 bands, 24 bands, and the price is quite cheap, you don't know the designer is deceived or deceiving others! In addition, there are a lot of claims [consumer recommended products] 8 or 9 band of short-wave radio, caused by a market malignant competition, short circuit, in addition to the band switch, almost no other components. Instead of buying such a radio, I suggest buying a traditional 3, 4-band short-wave radio. 3. The second frequency CONVERSION technology of shortwave radio (SW DUAL CONVERSION) shortwave radio was originally using direct amplification circuit, in the 50 s, used a frequency CONVERSION circuit, which is usually says superheterodyne receiver. In order to further improve the sensitivity, selectivity and anti-jamming capacity of radio receiver, scientists have developed a multiple frequency conversion technology, of course, the first is applied in the field of wireless communication, then transplanted to the advanced radio, thus greatly improves the performance of the short-wave radio. The portable high-sensitivity short-wave radio usually adopts secondary frequency conversion, while the more advanced professional short-wave communication receiver, or even three or four frequency conversion techniques. 4. The phase lock loop (PLL), digital tuner type technology of radio phase-locked loop digital radio tuner type technology, is the contemporary microelectronics application technology of high and new technology products, integrating advanced, the characteristics of practicality, novelty. 1. Using single chip microprocessor chip as the core of the digital tuning system, and contains the phase lock loop (PLL) frequency synthesis, primary frequency, multi-function digital clock control and LCD digital display and other advanced features. With high precision and high stable quartz crystal as the frequency base, the frequency of receiving station is locked, no drift phenomenon. Have a frequency memory function. Generally speaking, digital tuner type radio storage station number, the better, the more advanced digital tuner type should have direct input on the radio frequency, digital and analog tuning knob on the electronic circuit is often secondary frequency conversion technique is used to improve performance. The disadvantages of digital tunics are that the circuit is complex, the design is difficult, the requirement of the component is strict, the cost is high, the production debugging is very complicated. Due to the components, the static electricity is bigger than ordinary radio, sensitivity and selectivity of affordable digital tuning the radio is not higher than good pointer to simulate the radio a lot. A radio that USES digital display frequency technology, which USES traditional analog receiving circuits, is not expensive and can easily be used for high performance indicators. The difference is that the digital display replaces the traditional radio's pointer to the frequency and adds the electronic clock control. More compact and convenient than digital tunnable radio, it is a more efficient and practical radio variety. This type of defect is no memory radio function, because the traditional simulation receiving technology, the frequency accuracy and stability nor digital tuner type high on the radio.