What is the relationship between radio stations and mobile communication?

When a radio station plays a program, it first converts the sound into an audio signal through a microphone, and then modulates it with a high-frequency signal (carrier wave). At this time, a certain parameter of the high-frequency carrier signal changes correspondingly with the audio signal, so that the audio signal we want to transmit is included in the high-frequency carrier signal, and the high-frequency signal is amplified again. Then, when the high-frequency current flows through the antenna, a radio wave is emitted outward, and the propagation speed of the radio wave is 3×108m/s. This radio wave is received by the radio antenna, then amplified and demodulated, and then restored to an audio signal, which is sent to the speaker voice coil to cause a paper basin.

The medium wave frequency (high frequency carrier frequency) is defined as 525- 1605 kHz (thousand cycles).

The frequency range of short wave is 3500- 18000 kHz.

Superheterodyne radio principle

Figure 3-2 is the working principle block diagram of AM superheterodyne radio. The high-frequency signal received by the antenna and the local oscillation frequency of the radio station (its frequency is a fixed intermediate frequency higher than the external high-frequency signal, and the intermediate frequency standard in China stipulates 465KHZ) are sent to the frequency converter for mixing conversion, and a new frequency is generated in the load loop (frequency selection) of the frequency conversion stage, that is, the intermediate frequency generated by the difference frequency (B in Figure 3-2). The intermediate frequency only changes the carrier frequency, and the original audio envelope has not changed. It can better amplify the intermediate frequency signal, detect the intermediate frequency signal and filter out the high frequency signal (D in Figure 3-2). After low amplifier and power amplifier, the speaker is driven to sound.

Brief introduction of the working principle of this machine. See Figure 3-3 for the circuit diagram of the antenna input loop composed of C 1 and B 1. VT 1, B2, B 1 and c constitute the frequency conversion stage. VT 1 is a frequency converter. The primary coil and c constitute the load of the frequency conversion stage. C 1 and B2 constitute a local oscillator circuit, C6 an oscillation coupling circuit, VT2 and VT3 an intermediate frequency amplifier circuit, 2AP9 a detector circuit, R9 a volume potentiometer (with power switch), and C 16 a high frequency coupling capacitor.

VT4 and VT5 are pre-low frequency amplifier stages, and VT6 and VT7 are class B pull power amplifiers. R 16, C2 1 and C 17 are power wave circuits. R 1，R2，R3，R4，R5，R6，R7，R 12，R 10，R 1 1，R 13，R 17，R 18。

Radio shorthand

Installation of superheterodyne radio:

① Analyze the circuit of the whole machine and be familiar with the installation position of components on the printed board.

(2) Welding and installation of components (check the quality of components during installation).

③ Check the circuit, compare the installed radio with the circuit schematic diagram, and check the following contents.

A. Check whether the models, installation positions and pins of transistors at all levels are correct.

B. Check the installation sequence of intermediate weeks at all levels, and whether the first-level outlet is correct.

C. check whether the lead of electrolytic capacitor is connected correctly.

D. Whether the initial installation position of the segmented magnetic antenna coil is correct.

E. measure the resistance of the whole machine with pointer multimeter R× 100, connect the negative lead of the power supply with a red stylus and connect the positive lead of the power supply with a black stylus, and the measured resistance of the whole machine should be greater than 500 ohms.

Only after the above inspection is correct can the 4.5 volt power supply be connected.

Debugging of superheterodyne radio. Newly installed radio. Only through adjustment can we meet the requirements of performance indicators. The adjustment contents include: adjusting the operating points of transistors at all levels, adjusting the intermediate frequency, adjusting the coverage (that is, adjusting the calibration) and adjusting the frequency tracking (that is, adjusting the sensitivity).

Here are the contents and methods of adjustment:

① Adjustment of static operating point: Each transistor has different functions and different operating points. The adjustment of static operating points at all levels is measured by the voltage on the emitter resistance of each transistor when there is no signal (local oscillation stops) and no external signal. Adjust R 1, R4, R 12, R 17 and R 18 in stages, so that the voltage level of VT 1 is-0.5 ~ 0.7v ... and the voltage on the level R6 of VT2 is-0.5 ~ 0.

② Intermediate frequency adjustment: The purpose is to adjust the resonance frequency of three intermediate frequency transformers (intermediate frequency tuning circuits) to a fixed intermediate frequency of 465KHZ. Because the intermediate frequency used is new, the general manufacturers have adjusted it to 465KHZ. Therefore, when debugging, when receiving the radio station, adjust the magnetic core of the intermediate frequency with a non-inductive screwdriver, and the adjustment sequence is from the back stage to the front stage, that is, adjust Bz3 first, and then adjust Bz2 until the speaker is loudest.

③ FM coverage (adjust the frequency range of the radio to 535- 1605 kHz): adjust a dial on the fashion, so that all the double variable capacitors are screwed in and out. Turn the double variable capacitors on the lines of 530- 1630 kHz respectively, so as to align the pointer with the 640 kHz scale (china national radio). Turn the magnetic core of the oscillating coil with a non-inductive screwdriver and listen to the radio broadcast at 640 kHz. Adjust the fine-tuning capacitor C3 of the oscillating circuit, receive radio broadcast around 1500 kilocycles, and repeatedly adjust the high-end and low-end for several times.

④ The purpose of unified tuning (frequency tracking adjustment) is to make the local oscillator frequency within the receiving frequency band (intermediate frequency band 535 ~ 1650 kHz), which is 465KHz higher than the external signal frequency, that is, the local oscillator frequency range is 1000 kHz ~ 2070 kHz. Therefore, the synchronous adjustment is carried out with the variable capacitor with the same capacitance of C 1 and C2 double connection, and usually the high, middle and low points in the selected frequency range are tracked, that is, the three-point unified adjustment. In order to achieve good three-tracking, a pad capacitor C is connected in series in the local oscillator circuit, a fine-tuning compensation capacitor C is connected in parallel in the input circuit for specific adjustment, and then the compensation capacitor Cz of the input circuit is adjusted to maximize the volume.

Adjust the mid-range to listen to the broadcast around 1000KHZ to make the sound maximum. At this time, adjust the C-piece on the flower piece of the double capacitor rotor, and dial out the distance between the pieces. If the input is reduced when the pattern is dialed, the middle end will not be detuned and the pattern will be dialed back to its original position. If the input increases, you need to touch the edge lace to compensate, and you can also change the capacity of the pad capacitor.

1. Recently, the global economic situation is grim, and more and more enterprises have begun to be impacted, and the profit margin has intensified and declined. In order to control costs, layoffs and salary reduction have become the most commonly used and preferred methods for enterprises. Unemployment and survival pressure have become the words that have attracted much attention recently. According to the prediction of experts of the International Labour Organization at the beginning of this year, the number of unemployed people in the world will reach another record in 2009, reaching 2 1 10,000. In China, real estate, finance and other enterprises are also rapidly laying off employees.

Second, employment pressure.

The global financial tsunami is quietly spreading to the employment market of college students. On the one hand, it is estimated that 1 10,000 college graduates will be unemployed by the end of 2008, and 5.92 million college graduates will graduate in 2009, plus tens of millions of unemployed college students who have not been employed in the past; Postgraduate enrollment expansion policy is not optimistic. Expanding enrollment is nothing more than shifting the current employment pressure to the next few years. If the employment pressure is not cushioned by the capital, it may be difficult for graduate students to find jobs in the future. On the other hand, many enterprises have cancelled campus recruitment plans, and the 2009 college students have already felt the "cold current" of employment prospects. From this cartoon, we can see that the employment demand of graduates is far from the number of jobs in enterprises. Under the financial turmoil, the employment prospects of graduates are not optimistic. The hot scene of the job fair also confirms this point.

Judging from the previous employment forms, the 10 majors with the highest monthly salary are French, petroleum engineering, registered accounting, software engineering, German, microelectronics, architecture, information security, insurance and Japanese. The 10 majors with the lowest monthly salary are clinical medicine, primary education, traditional Chinese medicine, education, fine arts, medical imaging, forestry, history, physical education and musicology. Despite the poor employment situation in 2009, there are still many opportunities for job seekers in some industries. According to the analysis of talent index in 2008 and the forecast of talent market in 2009, three industries occupied the limelight in the past 2008 and are expected to continue their prosperity in 2009, namely, information technology and internet industry, construction industry and fast-moving consumer goods industry;

The demand for talents in the information technology and Internet industries has always been the highest in the whole year, ranking first among the top ten hot industries every month, and the recruitment has always maintained a market share of around 15%-20%. Judging from the demand for talents in the industry, the demand for technical talents is on the rise, and the demand for software talents is the hottest.

Online job demand shows that in 2008, the proportion of software industry recruitment increased by 5.3% compared with 2007; The demand of IT industry ranks first. The demand for software engineers will continue to increase in the next few years.

First, consider income: a person's income is related to the profit level of the industry, the nature of the industry and personal ability. Let's compare the general traditional industry with the IT industry! How high do you think the profit level of traditional industries is? At most 15%, that is to say, the income of the enterprise is 100 yuan, and the profit is only 15 yuan. The boss can give you 1 yuan at most. If it is an IT industry, the profit is at least 60% of the income 100 yuan, and the boss can at least give you 4 yuan, then the salary of employees in IT enterprises is four times that of employees in traditional industries.

Secondly, income is divided into actual income and expected income. It depends not only on how much money you can get now, but also on how much money you can get in the future, right? For example, there are two jobs, one is 2000, and the other is 1500. Which job would you choose? Ok, now let's add another condition: the annual growth rate of 1500 is 40%- 100%, while the annual salary in 2000 was 1%. Now which job do you choose first? What you are doing now, consider how much technical content there is, and why Chinese medicine doctors and lawyers are more valuable as they get older. Because their jobs are high-tech, their current jobs can be old, so their value is increasing.

Second, consider development: now is the information society, and IT enterprises are developing the fastest. If they are engaged in traditional industries, of course, their development will be slower. The national average GDP will increase by 9% every year, which is very high (according to the figures of the National Bureau of Statistics, for every 1 percentage point increase, nearly 654.38+ten thousand people will be laid off), and the IT industry will increase by more than 40% every year. There has been a breakthrough in recent years. Such rapid development will inevitably lead to the scarcity of technicians, so it is relatively easy to enter this industry as long as you master practical skills. Moreover, the IT industry is a knowledge-intensive enterprise, and its development depends on the increase in the number of employees. For example, the business of our company grows by 65,438+000% every year, which means that the number of employees increases by 65,438+0 times every year on the basis of the previous year. Then the increased position must be managed. These positions come from your old employees. Soon you will have the opportunity to become the manager of this industry. So there are many young bosses, general managers and managers in this industry, which is incomparable to traditional industries.

Third, consider stability: What kind of job is stable and not easy to lose? A patient needs surgery. Are they afraid of surgeons? Of course, because they control the patient's life. Software engineers are just like surgeons in IT enterprises. If the software engineer is unhappy, the information system of the enterprise may go wrong, and the financial data and production data of the enterprise may disappear. Because they hold the core technology of the enterprise and the lifeblood of the enterprise. Do you think companies dare to fire such people at will? Is such a person stable at work? Of course it is stable. If the current work technology is too low, no one in the enterprise will have any great influence, right? This is the root cause of people's insecurity.

Fourth, consider social status: a person's social status depends on his salary, the industry he is engaged in, and the public's cognition of the industry. If his salary is low now, it may be because he is engaged in a recognized sunset industry and his social status is definitely not high. If you enter the IT industry, the situation is completely different. With high salary and modern office conditions, you belong to the sunrise industry and your social status will naturally be high.

5. Consider safety: Safety: It depends on occupational safety and occupational welfare. The welfare of IT industry is more perfect.

The software engineer course of Beida Jade Bird (Lanzhou Siwei) embodies the teaching objectives in theoretical knowledge explanation and project actual combat development, comprehensively improves students' professional technical knowledge and project actual combat ability, makes theoretical courses, computer courses, stage project courses, project case courses, project defense, graduation project and other links standardized and strictly assessed, ensures students' excellent professional skills and excellent professional quality, and becomes the object of competition among enterprises.