the AM frequency we want and filter out the other frequency bands. LC resonance is a ... Caution: 1. The diode has polar
Crystal Radio KV3540/AK9823/AK23/K23
Advise:
Make sure there is correct number of components in your package. Use 30W iron, 60% solder. Take extra caution against overheating during soldering process. Transistors and ICs can be easily damaged by high temperature so do not leave the iron on the board for too long. Too many or too little solders may cause a defected circuit. Please weld the IC socket first then plug in the IC chip.
Circuit Principal:
The place we live on earth is filled with electric 1112.gnetic waves, which are produced by human. Radio station transmit all the usable information at high frequency, through the antenna we receive these signals, then after some processing it is possible to obtain the original information. AM broadcast is using high frequency carrier with low frequency signal. It transmits the original signal by amplitude modulation of the high frequency carrier wave. To receive the signal from the air, we need an antenna. Antenna for AM channel is not very strict, usually larger area and less obstruction will have better reception. Signal received by the antenna is very weak and covers a wide band, so ,ve need to separate the AM frequency we want and filter out the other frequency bands. LC resonance is a good filtering circuit. We get maximum impedance when the frequency is equal to the formula. Using an inductor and one variable capacitor we can produce different frequencies base on different LC values. We can select different radio channels in thls way. However the channel received is still in high frequency signal range and can't be beard by human ear, we need to remove the high frequency carrier wave. Diode conducts in positive direction only so used with RC filter we can demodulate the original signal. With a sensitive earphone you can receive clear AM channel. No electricity is needed! This is the first generation semi-conductor radio invented in World War IL If living in city area, place the antenna stick out of window, and put the earphone on, rotate the variable capacitor to receive radio channels. Adjust the antenna and it's direction can improve reception, if still not satisfy, get a outdoor antenna. Caution, never connect to ground, equal potential and phase will 1 cancel out the signal received. F01mula: f = 2 ir ,jLC
Circuit Explanation: Electric wave received by antenna pass through the coupling capacitor Cl to LC circuit (consist of inductor Ll and variable capacitor VCl). Use an adjusting stick to slowly adjust capacitor to the required frequency. (Fig. 1 is ANI amplitude modulated wave). The frequency signal selected pass through the diode then through the filtering circuit R2 and C2. Finally the sound signal is send to the earphone through the coupling capacitor C3. Carrier
Caution: 1. The diode has polarity, antenna need to be straighten up. 2. If sound signal is. very weak, point the antenna to a direction with less obstruction. Make close contact to large metal plate to increase the receiving sensitivity. 3. The earphone must be tight with ear without any gap. Fig. 1
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Parts list: Remark Component Serial No. Qty. 1 GnBIGnGo 5.6MO Rl ReBkGnGo. 1 R2 2MO 3300pF I 332pF Cl 1 C2 33pF 1 IOµF C3 1 DI Diode Variable capacitor 1 VCl 1 Inductor (A11) Ll 1 Earphone Earphone 1 Antenna 1 K23 PCB Code: Bk:Black, Re:Red, Gn:Green, Bl:Blue, Go:Gold. (a) Sound signal
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