Troubleshooting of radio 1. Input tuning circuit
The circuit from the receiving antenna to the input end of the frequency converter is called the input circuit.
The input tuning loop consists of magnetic antennas T 1 L 1 and L2, and tuning capacitors CA, CA and CA‵ form a series resonant circuit. Magnetic rods have high magnetic permeability. When it is parallel to the propagation direction of electromagnetic field, a large number of spatial magnetic lines can be gathered, thus inducing a high external signal on the tuning coil L 1 wound around the magnetic bar. By adjusting the capacity of the double capacitors from maximum to minimum, the resonant frequency of the tuning circuit can be continuously changed in the lowest range from 535KHZ to 1605KHZ.
The radio receiving station uses the frequency selection characteristics of the resonant circuit to tune different stations. Suppose that the magnetic antenna receives four radio signals with frequency bits of f 1, f2, F3 and F4 in the receiving frequency band, and the antenna coil L 1 generates corresponding induced electromotive forces E 1, E2, E3 and E4. In the input circuit, L 1 is fixed and CA changes continuously. When CA rotates, the natural frequency of the input circuit will change. If you want to listen to the radio broadcast with frequency f2, you can find that the natural frequency of the input circuit is equal to the radio signal f2 by rotating the variable capacitor CA, that is, the input circuit is tuned to the frequency f2, at this time, the current value generated by E2 in the circuit is the largest, while the current values of E2, E3 and E4 are the smallest because of detuning, so the radio signal with frequency f2 is selected.
Second, the intermediate frequency amplifier stage
The function of the intermediate frequency amplifier stage is to amplify the 465KHZ signal sent by the frequency conversion stage, output an intermediate frequency modulation signal with sufficient amplitude, and send it to the detector. Generally, it is required that the passband center of the IF amplifier is 465KHZ, that is, 460.5? 469.5 kHz
Three, detection stage and automatic gain control (AGC) circuit
The function of the detector is to detect the low-frequency (audio) signal from the intermediate frequency amplitude modulation signal and send it to the low-frequency amplification stage for amplification. Triode detection is to input an intermediate frequency signal from the base of the triode and output it from the emitter, using the unidirectional conductivity of the emitter. Because the transistor has amplification function, it can combine detection and amplification properly, which greatly reduces the power consumption of the circuit and improves the gain of the whole machine.
For the emitter junction of transistor VT3, the power supply is forward biased through R4 and R3. On the positive half axis of the signal, the emitter junction of the transistor is turned on, and the negative half axis is turned off, resulting in a unipolar voltage on the emitter load resistor RP. Capacitor C5 filters out the residual intermediate frequency to obtain a low-frequency signal, which is input to a low-frequency amplifier and amplified by the center tap of RP. The function of AGC circuit of automatic gain control is that when the signal is strong, the AGC circuit starts to control, so that the gain of the intermediate frequency amplifier decreases, and when the signal is weak, the AGC does not act.
The gain control process is as follows: VT2 and VT3 transistors are used as bias resistor R3. When there is no signal or the signal strength is constant, the base potential and point A potential of transistor VT2 remain unchanged. When the external signal becomes stronger, the base potentials of transistors VT2 and VT3 will increase, the collector current of VT3 will increase, and the potential at point C will decrease. Because of the bias resistance, the potential of point A at point B will decrease and the base potential of control VT2 will increase.
Fourthly, the low-frequency amplifier stage.
After detection, the output audio signal is sent to an audio amplifier for amplification through a coupling capacitor C6 to increase the amplitude of the audio signal, and then sent to a power amplifier for amplification.
Pay attention to the use and maintenance of the radio when you start using it? Running in? Running-in is a term used in cars, which requires users to drive in strict accordance with the instructions to make the car reach the best use state. So is the radio. All parts need to be run-in for a period of time before they can start to work at their best. When I use a new radio, it usually takes about 3 days to run in. During the running-in period, the startup time is generally limited to less than 5 hours, and the volume can be turned on to half.
At the end of the running-in, gradually extend the listening time, turn up the volume of the radio, and you can listen normally, or further transform it in your own way.
As for listening habits, I generally avoid turning on my mobile phone when electromagnetic interference is strongest (such as noon), so as to protect myself? Room? Our speakers and receiving parts are inviolable. (personal opinion)
When listening at night, I got into the habit of turning off my phone when I was sleepy, which avoided some unnecessary waste and loss. In addition, put the radio beside your bed, not beside your bed, to prevent yourself from crushing the radio or its accessories unconsciously, so as not to wake up with the remnants of the radio. Hehe, at the same time, it also avoids repeated investment because of buying accessories. (Money-obsessed mentality, see the official grasp)
In the way of listening, especially in the SW band, it is inevitable to encounter strong interference. At this time, you need to patiently receive the same radio signals on other frequency points, and believe that the frequency of a radio station is not just a frequency point. Ha ha.
Finally, talk about the maintenance of radio. After using the radio for a period of time, it is inevitable that dust or other things will enter the machine. The dust will be removed at this time. Regular maintenance has a great bearing on the life of the radio.
Common sense transistor radio 1, the choice of power supply.
Transistor radios are generally powered in three ways:? Is to use dry batteries; The second is to use the transformer, rectifier circuit and regulated power supply inside or outside the radio, and use DC power supply to supply power; Third, the above two methods are both.
When the radio volume decreases, sensitivity decreases and noise increases, it may be a sign that the battery is about to run out. Replace the battery in time to prevent the battery from leaking and internal parts from rusting.
For a radio powered by a dedicated regulated power supply, the maximum power supply of the regulated power supply should have a certain margin compared with the power consumption current of the radio to ensure that the radio and the regulated power supply can work normally. The DC output voltage of the regulated power supply must be consistent with the working voltage of the radio. If the voltage is high, it is easy to damage the radio. When the voltage is low, not only the output power decreases, but also other characteristics will change.
Step 2 use an antenna.
The directionality of the radio receiving station depends on the magnetic antenna in the machine. When receiving, the magnetic antenna rod in the machine should be aimed at the direction of the radio station, which has the highest receiving sensitivity. When receiving short wave and FM band, pull out the rod antenna. In the case of poor reception conditions, an external antenna can be used to improve the listening performance of the radio, but lightning arrester must be installed at the same time. Don't listen to the radio during a thunderstorm to prevent lightning strikes.
3. Volume.
The power consumption of transistor radios using dry batteries increases sharply with the increase of volume. Therefore, in order to prolong the battery life, it is not advisable to turn the volume too loud. At the same time, in order to make the sound from the speaker soft and beautiful, it is best to turn on the volume appropriately, reaching 70% ~ 80% of the maximum volume.