Production of superheterodyne radio
1. Principle part :
Superheterodyne radio : The superheterodyne radio converts all received high-frequency signals of different frequencies into a fixed intermediate frequency signal for amplification, so the amplification of various radio signals by the circuit is basically the same, which can make The intermediate amplifier circuit has excellent frequency characteristics.
Advantages and disadvantages of superheterodyne radio:
Advantages :
1. High sensitivity and stable operation: narrow-band amplifiers can be used for medium amplifiers. High gain can be achieved relatively easily, and the work is relatively stable. Higher sensitivity and stability can be obtained. Directly amplified high-amplifiers must use broadband amplifiers, which are difficult to achieve when the gain requirements are high, and the work is also unstable.
2. Good signal selectivity and high signal-to-noise ratio: the intermediate stage uses a narrow-band amplifier, which is selected by multiple resonant circuits. It has strong selectivity and high signal-to-noise ratio.
3. Roughly the same sensitivity to different stations: Since the broadcast signal of any station becomes a fixed-frequency intermediate frequency signal and then amplified during reception, it has roughly the same sensitivity to different stations.
Disadvantages :
- Image interference (an interfering signal that is two intermediate frequencies higher than the received frequency).
- False response (non-linearity of frequency conversion circuit).
Second, the production and debugging part:
Use a multimeter to measure each component before manual welding. When installing, first install larger components (such as mid-week, transformers), then install low-profile and heat-resistant components (such as resistors), and finally install heat-resistant components (such as triode). Resistor installation: After selecting the resistance value of the resistor (refer to the schematic diagram for calculating the resistance value explained earlier), bend the resistor feet according to the distance between the two holes. It can be installed horizontally close to the circuit board, or vertically. Unite. The length of the ceramic capacitor and triode should be moderate. Don't cut it too short, and don't leave it too long. They should not exceed the length of the middle circumference. Too high will affect the installation of the back cover. The four lead ends of the magnetic rod coil can be directly tinned by rubbing back and forth with a soldering iron and rosin solder wire several times, and the four lead ends are correspondingly soldered to the copper surface of the circuit board. Since the double-connected disc for tuning is installed very close to the circuit board, the protruding part of the component feet in its circumference should be cut off with diagonal pliers before welding, so as to avoid obstacles during installation or tuning. The components for dial tuning include the pins of B2 and B4, the switch pin of the potentiometer and a pin.
Speed: The speed should be fast when soldering, so as not to burn the plastic part of the circuit board and cause poor contact. In electronic production, the connection of components needs to be soldered. The quality of welding has a great influence on the quality of production. so learn
In order to make electricity, it is necessary to master the welding technology and practice the basic skills of welding. Before the formal welding training started, we first got to know the following welding tools:
(1) Electric soldering iron. The electric soldering iron is the most commonly used welding tool. In this practice, we used a 30W long-life electric soldering iron.
(2) Solder and flux (rosin). Solder can not only fix the components, but also ensure a reliable current path.
(3) Auxiliary tools. Such as: needle-nose pliers, diagonal pliers, scissors, etc.
1. Adjustment of the static working point of the triode. It mainly makes the triode work in the best state statically by changing the resistance value of the bias resistor on the triode.
2. Adjust the receiving frequency range. It realizes the medium wave frequency received by the radio by changing the inductance of the medium wave oscillating coil and the fine-tuning capacitor of the local oscillation circuit, and the frequency range is 5 2 5 ~ 1 6 0 5 kHz.
3. System adjustment, also known as sensitivity adjustment. It adjusts the position of the antenna coil on the magnetic rod (changing the inductance of the antenna coil) and fine-tuning the capacitance of the input loop, so that the radio always has f=465kHz in the receiving frequency range.
Highlights :
- Welding was smooth and there was no error: At the beginning, the welding resistance was measured with a multimeter, and the resistance value was accurately confirmed, so the welding went smoothly, and there was no problem of wrong welding of capacitors; when welding capacitors and other components, pay great attention to the positive and negative poles of electrolytic capacitors In the end, the radio successfully listened to the sound, which also proved that the welding was accurate, and there was no wrong welding.
- The welding is fast and the finished product is good: I soldered the radio on the first afternoon when I went to the laboratory, and I successfully listened to the program by the window. I was very excited at that moment and became the fastest soldered. Test results were good, the radio was loud and clear.
It is troublesome to determine the positive and negative poles of more than a dozen resistors and multiple electrolytic capacitors during the welding process. It is troublesome to distinguish capacitors by color, so I use a multimeter to measure the resistance value of all resistors and classify them according to the resistance value. This saves a lot of time in the welding process, which I think is better. Makes me weld faster, so being organized makes things faster and easier to do.
There are many components in the soldering process, and the pins that need to be soldered are very dense, so I am extra careful when soldering to prevent wrong soldering. The dense pins are easy to lead the solder at one point to another point, causing short circuit and other faults, making the circuit unable to work normally, so extra care must be taken.
In fact, the soldering process is not smooth. For example, the pins of the double capacitor are too wide and the opening of the circuit board is too narrow. The pins must be narrowed with pliers to install, and so on. In the process of solving these problems, I have cultivated my patience and exercised my ability to troubleshoot faults, and I have gained a lot.