Long-distance remote control encoding and decoding transmitting and receiving component circuit

The so-called long-distance remote control encoding and decoding transmitting and receiving components are high-power transmitters (transmitting power 2~5W) that use digital encoding chips such as (MC145026, PT2262, etc.) to modulate signals, and are coupled with high-sensitivity receivers (receiving sensitivity not inferior to 1.5μV) and decoding circuit paired with the encoding chip (such as MC145027, PT2272, etc.) for long-distance wireless remote control, alarm and other purposes. Figures 1 and 2 are the circuit diagrams of the codec remote control transmitting/receiving components produced in Guangdong compiled by the author during actual maintenance. Figure 1 is the transmitter and Figure 2 is the receiver. The sending and receiving distance is up to 5 kilometers. Transmitter component circuit principle The main technical parameters of the transmitter component are as follows: FM system; operating frequency 36.1MHz; power supply voltage 12V, emission current less than or equal to 1.5 amps. The transmitter component consists of coded signal generation, modulation signal amplification, transmitter local oscillator, 3 times frequency, high frequency amplification, high frequency power amplification circuit, antenna matching network, etc. The coding signal generation circuit is completed by the special coding integrated circuit U101 (PT2262), and the modulation signal amplification circuit, transmitter local oscillator circuit, and pulse (square wave) modulation circuit are completed by U102 (MC2833). The modulated high-frequency signal is output from the pin of U102, and the 3 times frequency (36.1MHz) signal of the local oscillator is selected through L103, T101, L104, and C119 as the operating frequency of the transmitter. T101 and T102 form a two-stage high-frequency pre-voltage amplifier (T101 also serves as the first amplifier). After power amplification by T103, it passes through C130, L108, C131, C132, L109, C133, L110, C13 4 sections composed of " Inverted L-shaped frequency selection network, the antenna TX101 radiates electromagnetic wave signals into the air. Receiver component circuit principle The main technical parameters of the receiver are as follows: receiving frequency 36.1MHz, working voltage +12V, receiving sensitivity not inferior to 1.5μV. The receiver circuit is composed of high amplifier, frequency conversion, medium amplifier, frequency identification and demodulation, low frequency pulse amplification and shaping, decoding circuit, etc. The high-amplification circuit consists of two-stage double-gate field effect transistors T201 and T202 as high-amplifier tubes, and the first mixing is completed in the second high-amplification stage. J201 (15.6MHz), T204, L204, etc. form the first local oscillator. , the oscillation frequency is 46.8MHz, three times the fundamental frequency J201; the local oscillator frequency and the externally received frequency (36.1MHz) are used to extract a 10.7MHz difference frequency signal through T202, L203, J202, etc., as the first intermediate frequency signal. After being amplified by T203, it is sent to the pin of U201 (MC3361). This intermediate frequency signal is then combined with the second local oscillator composed of U201, the internal circuit of the pin and J203 (10.245MHz) to produce a 10.245MHz second local oscillator signal, which completes secondary frequency conversion inside U201, from U201 The 455kHz pin outputs a difference frequency signal of 455kHz. This 455kHz signal is used as a new intermediate frequency signal and is filtered by J204 bandpass. It is returned to the internal circuit by the U201 pin for IF amplification and frequency identification demodulation circuit. Finally, the carrier modulation signal is demodulated by the MC3361 pin. (low frequency pulse train). The external coil L205 connected to the pin of U201 is the frequency identification adjustment coil. The demodulated low-frequency pulse signal is sent to the T205 amplification circuit through R219, C230, and R220 for amplitude amplification, and then is amplified and shaped by A, B, and C of the U203 Schmitt trigger MC140106, and then sent to the decoding circuit. The decoding circuit is completed by the integrated circuit U202 (PT2272) paired with the encoding circuit. Only when the potential of the pin of the encoding chip (PT2262) is completely consistent with the potential of the pin of the decoding chip (PT2272), the pin of U202 will have a high-level output, which can be used as a driving signal for other control interfaces and applied to various controls. Common fault handling Common faults in transmitter components are damage to transistors T101, T102, T103, J101, etc. The damage to T102 and T103 is manifested by the fact that the transmitting current of the whole machine is large (more than 2A) or too small (400mA or lower), and the transmitting distance is tens of meters or several meters; the damaged transmitting distance of T101 is only about 1 meter, and the current of the whole machine is average Not more than 100mA; if J101 is damaged, the transmitting current of the whole machine will drop below 10mA, and the signal cannot be transmitted. Common faults of receiver components are damage to T201 and T202 or the oscillator stops vibrating. T201 damage mostly occurs during thunderstorm seasons and is damaged by lightning strikes; oscillator failure is mostly caused by crystal failure or transistor damage. Another common fault of the receiver component is the parameter change of the coil L205, which can be eliminated by fine-tuning the core fault.