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With the development of science and technology and the wide application of high and new technology, electronic technology is playing an increasingly important role in all fields of the national economy, and is deeply infiltrating into all aspects of people's life, work and study. The new century has entered the information society based on electronic technology, and new electronic services and new electronic facilities are emerging one after another, almost everywhere. Mastering certain electronic technology knowledge and skills is the requirement and call for every electronic professional in the electronic information age, and it is also the need to learn this major.

This radio experimental training course is mainly designed according to the study of electronic information specialty. The arrangement of high-frequency electronic technology is to learn the basic principle and working process of radio wave transmission and reception and receive radio.

Computer includes these two aspects, which combines the knowledge of digital electronic technology, analog electronic technology, modern communication technology and the knowledge of common electronic components. It can cultivate students' ability to analyze and solve problems, integrate theory with practice and practical operation ability, and greatly improve students' comprehensive learning ability. Therefore, this training is very necessary.

1. Internship content:

(1) Learn to recognize simple electronic components and circuits;

(2) Learn and master the working principle of the radio;

(3) Weld the components according to the drawings, assemble a radio, and master its debugging method.

Introduction of practice equipment:

(1) Electric soldering iron: Because there are many components to be soldered, an external heating electric soldering iron is used, with a power of 40.

(2) screwdriver, tweezers and other necessary tools.

(3) Rosin and tin, due to the low melting point of tin, the solder can move quickly when welding, and it is firmly welded on the metal surface, and the solder joint is bright and beautiful.

(4) Two No.5 batteries.

The meaning of three purposes is familiar with the use, maintenance and repair of common tools for manual soldering. Basically master the welding technology of manual electric soldering iron, and can independently complete the installation and welding of simple electronic products. Familiar with the production process of electronic product installation technology, the steps and methods of printed circuit board design, the process of hand-made printed circuit board, according to the circuit schematic diagram, physical components. Understand the category, model, specification, performance and application scope of common electronic devices, and be able to consult relevant electronic device books. Be able to correctly identify and select common electronic devices, and skillfully use ordinary multimeter and digital multimeter. Understand the welding, debugging and maintenance methods of electronic products. Through the monitoring and debugging of the radio, we can understand the production and debugging process of general electronic products, learn the methods of debugging electronic products initially, and cultivate the detection ability and meticulous scientific style.

Experimental principle and steps: 1. Circuit structure of superheterodyne radio: The superheterodyne radio is characterized by frequency conversion (frequency conversion) and adopts a fixed tuned intermediate frequency amplifier. Generally, it includes the following parts: frequency conversion stage, intermediate frequency amplification stage, detection stage, low frequency preamplifier stage and low frequency power amplifier stage. The frequency conversion stage includes a mixer and a local oscillator. The high frequency amplitude modulation signal received by the antenna is sent to the mixer of the frequency conversion stage through the tuning loop and selection. The local oscillator circuit always tracks the received signal and generates a constant amplitude oscillation signal with a fixed frequency, which is also sent to the mixer. The two signals sent to the mixer make use of the nonlinear characteristics of the amplifier to generate a new difference signal. After the frequency conversion stage, the high frequency amplitude modulation signal only changes the carrier frequency, and the modulation law has not changed, so it is still an amplitude modulation signal.

Superheterodyne radio principle

1. radio transmission: sound waves are converted into audio communication through electro-acoustic devices.

Signal, the modulator makes the high-frequency constant-amplitude oscillation signal modulated by the audio signal; The modulated high-frequency oscillation signal is amplified and sent to the transmitting antenna, converted into radio waves and transmitted.

2. Radio broadcast reception: The receiving antenna of the radio receives data in the air.

Radio waves; The tuning circuit selects the signal with the required frequency; The geophone will be very high

Restore the frequency signal to an audio signal (i.e. demodulation);

3. Radio communication (broadcasting also belongs to the category of radio communication) and transmission.

Receiving is summarized as the conversion process in three opposite aspects, namely:

Transmit information-low frequency signal, low frequency signal-high frequency signal, high frequency signal.

Digital-electromagnetic wave.

Modulation mode: using radio waves as carriers to transmit signals.

With, you can use different loading methods. It can be divided into radio broadcasting.

There are two modulation methods: amplitude modulation and frequency modulation.

Schematic diagram of work]

Print the original picture

Cleaning and installation of radio components

Firstly, welding short wires;

Secondly, according to the schematic diagram and printed circuit board, insert all components (you can shape them first and then insert them).

Then check, check, can be welded (note that the components should be close to the printed circuit board to make it firm).

Welding process:

Electric soldering iron: 20W internal heating type is selected, and the new soldering head will be tinned, otherwise it will be easy to "burn to death" and it will be difficult to use without tinning.

Solder: Use bright and fusible solder or welding wire.

Flux: It can decontaminate, contribute to heat transfer and welding, and make the solder joint firm. Commonly used neutral flux rosin or rosin alcohol solution (general welding wire contains neutral flux).

Welding: Welding is a physical process, which is a process in which solder penetrates the surface of the welded object at high temperature and even connects the welded object into a whole after cooling. So there are three conditions for welding: temperature, time and environment.

If the temperature is not enough, the solder can not get enough kinetic energy, and it is difficult to penetrate the surface of the object to be welded, which is easy to form virtual welding;

If time is not enough, the temperature will not go up, and if time is long, it will easily burn the welded object;

The environment has a direct influence on welding, and the time required for spot welding and surface welding is very different. Generally speaking, when you feel the solder oozing along the surface of the welded object like water, the electric soldering iron should leave and blow air to promote cooling, so as to weld a bright, smooth and reliable solder joint (welding can only be carried out after the above preparations are completed).

When welding, the welding head should keep good contact with the component pins and the printed circuit board. During the welding process (before the solder joint is reliably solidified), it is forbidden to shake the welding object.

When welding, beware of virtual welding and lap welding (adjacent solder joints are short-circuited by redundant solder). After lap welding occurs, it can be reheated with an electric soldering iron. After the solder melts, use tweezers to pass between adjacent solder joints at room temperature, and remove the soldering iron at the same time (if there is too much extra solder, you can suck some with the soldering iron first).

It is safer to use tweezers when welding. When using an electric soldering iron, be careful not to burn your skin and clothes. After welding, the redundant pins of the component should be cut off.

1, debugging

After all welding work is completed, carefully check whether there is any virtual welding or lap welding, and then turn on the power for debugging after inspection. Before preparing for power-on debugging, be sure to connect multimeter mA files in series at both ends of potentiometer switch (pay attention to polarity) and check the current of the whole machine. Whole machine current

Working point debugging

According to the characteristics of integrated circuit radio, the debugging of working point is mainly to measure the voltage of each pin of integrated circuit, whether it is close to the reference value. If there is a big difference, disconnect the power supply and check the fault carefully. Changing the value of R3 can change the voltage at the 16 pin.

3. Mid-week debugging

The current of the whole machine is normal, and the voltage of each pin of the integrated circuit is normal. When you touch each pin of the double variable capacitor with tweezers, there is a bright cackle (you can receive the radio)-indicating that you can debug the middle week. It has been debugged in the factory in the middle of the week, and it is difficult to debug in the middle of the week-it is best not to debug. If debugging is needed, remote stations near 1000KHZ can be received (to avoid the influence of AGC).

Fine-tune the core in the middle two weeks carefully (not too much at a time, it is best to remember the original position of the core) until the sound is satisfactory.

4. Three-point unified adjustment

The so-called three-point unified tuning means that the local oscillator frequency can track the frequency of the received signal by adjusting the position of the antenna coil of the magnetic bar on the magnetic bar, adjusting the middle circumference and adjusting the compensation capacitance of the double variable capacitors, and the difference frequency can reach 465KHZ at the low end, the middle end and the high end.

You can refer to the introduction of frequency conversion circuit, and compare the tracking curve of local oscillator to the frequency change of tuned received radio signal, which is helpful for understanding.

When low-end unified tuning, first receive the remote radio station near 600KHZ (to avoid the influence of AGC), aim the magnetic bar antenna at the direction of the radio station (at this time, the sound is relatively loud), and then adjust the position of the magnetic bar antenna coil on the magnetic bar to maximize the sound, and the low-end unified tuning is completed;

Mid-range unified adjustment is the same as mid-range adjustment;

In high-end unified tuning, first receive the remote station near 1500KHZ (to avoid the influence of AGC), aim the magnetic rod antenna in the direction of the station (at this time, the sound is relatively loud), and then adjust the compensation capacitance of the dual variable capacitance tuning joint to maximize the sound, and the high-end unified tuning is completed.

5. Overall effect

After the above careful debugging, the receiving effect of the whole machine should have some outstanding advantages of superheterodyne radio, such as uniform and stable receiving effect, high sensitivity and good selectivity.

6, fault inspection

There are many ways to check the fault. There are current measurement method, voltage measurement method, resistance measurement method, interference method, etc., which can be applied flexibly according to the actual situation.

The current measurement method can check whether the current of the whole machine is normal or not, and it is generally used before the whole machine debugging;

Voltage measurement can check whether the voltage of each pin of the integrated circuit is close to the reference value and whether there is any problem. It is generally used when there is a problem with the current inspection of the whole machine or when there is a problem with reception.

Resistance measurement method can check short circuit and open circuit, and can check the quality of various components ... Resistance measurement method should be carried out when the power supply is disconnected, and is generally used before the installation of the whole machine or when problems are found in the current inspection of the whole machine;

Interference method is mainly used to check whether the signal is unblocked, which is helpful to determine the fault range. It is generally used to find the fault before debugging the whole machine.

7 teacher acceptance

After nearly a week's internship, the radio station was finally completed. The next step is to give it to the teacher for inspection and acceptance, and give the results of this internship. During the acceptance, the teacher first checks whether the radio can work normally and whether it can be closed. If this requirement is met, the teacher will take apart the radio, look at the soldering of the circuit board and give points as appropriate. If there is something wrong with the radio at the time of acceptance, the teacher will patiently help the students troubleshoot and teach them to check the circuit. After the radio is debugged, it can be taken to the teacher for acceptance.