Radio frequency transceiver transmission is widely used in vehicle monitoring, remote control, telemetry, small wireless network, wireless meter reading, access control system, community paging, industrial data acquisition system, wireless tag, identity identification, contactless radio frequency smart card, small wireless data terminal, safety fire prevention system, wireless remote control system, biological signal acquisition, hydrometeorological monitoring, robot control, wireless 232 data communication, wireless 485/422 data communication, digital.

[Edit this paragraph] Technical indicators of RF transmitter module

3 15/433 transmitting module SR99 15: 1 main technical indicators, communication mode: AM 2, working frequency: 3 15MHZ/433MHZ 3, frequency stability: 75 kHz 4, transmitting power: ≤500MW 5. The working frequency of the data transmission module is 3 15M, and the frequency stability is extremely high. When the ambient temperature changes between -25 and +85 degrees, the frequency drift is only 3ppm/ degree. Especially suitable for wireless remote control and data transmission system. The frequency stability of acoustic resonator is second only to crystal, but the frequency stability and consistency of general LC oscillator are poor. Even if high-quality fine tuning capacitors are used, it is difficult to ensure that the tuned frequency points will not shift due to temperature difference and vibration. There is no coding integrated circuit in the transmitter module, but a data modulation transistor Q 1 is added. This structure is convenient to interface with other fixed coding circuits, rolling coding circuits and single chip microcomputer, regardless of the working voltage and output amplitude signal value of the coding circuit. For example, when a coded integrated circuit such as PT2262 or SM5262 is used, its data output terminal pin 17 is directly connected to the input terminal of the data module. The data module has a wide working voltage range of 3 ~ 12V. When the voltage changes, the transmitting frequency is basically unchanged, and the receiving module matched with the transmitting module can receive stably without any adjustment. When the transmission voltage is 3V, the transmission distance in the open area is about 20 ~ 50m, and the transmission power is relatively small, about 100 ~ 200m at 5V, and about 300 ~ 500m at 9V. When the transmission voltage is 12V, it is the best working voltage, and the transmission effect is good. The transmission current is about 60mA, and the transmission distance in the open area is 700. When the voltage is greater than l2V, the power consumption increases, and the effective transmission power is no longer significantly improved. This module is characterized by relatively large transmission power and long transmission distance, which is more suitable for communication under harsh conditions. It is best to choose a conductor with a length of 25 cm for the antenna, and it is best to stand when transmitting at a long distance. Due to the influence of many factors when transmitting radio signals, the actual distance is generally only half or even less than the nominal distance, which should be paid attention to when developing. The data module is modulated by ASK to reduce power consumption. When the data signal stops, the transmitting current drops to zero, and the data signal can be directly connected to the input end of the transmitting module through a resistor instead of a capacitor, otherwise the transmitting module cannot work normally. The data level should be close to the actual working voltage of the data module to obtain high modulation effect. It is best to install the transmitting module vertically on the edge of the motherboard and keep a distance of more than 5mm from the surrounding equipment to avoid being affected by the distribution parameters. The transmission distance of the module is related to the frequency and amplitude of the modulation signal, the transmitting voltage and battery capacity, the sensitivity of the transmitting antenna and receiver, and the transceiver environment. Generally speaking, the maximum transmission distance in an open area is about 800 meters. When encountering obstacles, the distance will be shortened. Due to the refraction and reflection in the process of radio signal transmission, some blind areas and unstable areas will be formed, and different transmitting and receiving environments will have different transmitting and receiving distances.

[Edit this paragraph] Technical indicators of RF super regenerative receiving module

3 15/433 Super Regenerative Receiving Module SR99 15 Super Regenerative Receiving Module Volume: 30x 13x8 Main technical indicators: 1, communication mode: AM 2, working frequency: 3 15MHZ/433MHZ 3, with stable frequency. Receiving sensitivity:-106DBM 5, static current: ≤5MA 6, working current: ≤5MA 7, working voltage: DC 5V 8, output mode: TTL level receiving module, working voltage 5V, static current 4mA, super regenerative receiving circuit, receiving sensitivity-105dbm, receiving antenna 25 ~ 30. The receiving module itself has no decoding integrated circuit, so the receiving circuit is only a component, and only when it is applied to a specific circuit for secondary development can it play its due role. This design has many advantages, and can be used in conjunction with various decoding circuits or single chip microcomputer, so the design circuit is flexible and convenient. The advantages of this circuit are: 1, there is a frequency selection circuit at the input end of the antenna, which does not depend on the frequency selection function of 1/4 wavelength antenna, and the external antenna can be shortened or even removed when the control distance is close. 2. The waveform at the output end is cleaner when there is no signal, and the interference signal is short needle pulse, unlike other super regenerative receiving circuits, which will produce dense noise waveform, so it has strong anti-interference ability. 3. The radiation of the module itself is very small, and the shielding effect of the reticular grounding copper foil on the back of the circuit module can reduce the leakage of its own oscillation and the intrusion of external interference signals. 4. The copper core inductor with skeleton is used for sealing after the frequency is adjusted to 3 15M. Compared with the circuit with adjustable capacitor to adjust the receiving frequency, the stability of temperature and humidity and the ability of resisting mechanical vibration are greatly improved. The adjustment precision of adjustable capacitor is low, and the adjustment range is only 3/4 turns, while adjustable inductor can realize multi-turn adjustment. The adjustable capacitor cannot be sealed after adjustment, because the approach or intrusion of various media, whether conductor or insulator, will change the capacitance of the capacitor and then affect the receiving frequency. In addition, when the unsealed adjustable capacitor vibrates, there is displacement between the stator and the rotor; When the temperature changes, thermal expansion and cold contraction will change the distance between stator and rotor; The change of humidity changes the capacity due to the change of medium; Working in humid environment for a long time will also change the capacity because of the oxidation of stator and rotor, which will seriously affect the stability of receiving frequency. Adjustable inductance can solve these problems, because the inductance can be sealed after adjustment, and the insulator sealant will not change the inductance.

[Edit this paragraph] Technical indicators of RF superheterodyne receiving module

3 15/433 superheterodyne receiving module SR99 15 superheterodyne receiving module size: 35x 13x8 main technical indicators: 1, communication mode: AM 2, working frequency: 3 16.8MHZ 3, frequency stability:. Static current: ≤5MA 6, working current: ≤5MA 7, working voltage, so RX33 10A integrated circuit introduction: RX33 10A is a wireless remote control and digital signal receiving integrated circuit specially produced by HMARK Company in Taiwan Province Province, including low-noise high-frequency amplifier, mixer, local oscillator, intermediate-frequency amplifier, intermediate-frequency filter, comparator, etc. It is a main frequency conversion superheterodyne circuit, which is packaged in a double-row 18-pin wide-body chip. The main technical indicators are as follows: working frequency: 150 ~ 450mhz, working voltage: 2.7 ~ 6V, working current: 2.6mA (using 3V power supply), receiving sensitivity:-105dbm (using 1k data rate and antenna matching), and maximum data rate: 9. After impedance transformation, the frequency selection network composed of C9 is input to the input end of RX33 10 internal high-frequency amplifier 14. The signal is amplified at high frequency (gain is 15 ~ 20dB) in the chip, and then mixed with the local oscillator signal (3 16.8M) by the mixer to generate an intermediate frequency signal of1.8m. The superheterodyne receiver requires high impedance matching of the antenna, and the impedance of the external antenna must be 50 ohms, otherwise it will have a great impact on the receiving sensitivity. Therefore, when using the common wire with the wavelength of 1/4, it should be 23 cm, so as to minimize the lead length from the antenna root to the antenna welding point of the transmitting module. If it can't be lowered, it can be connected by RF coaxial cable with characteristic impedance of 50 ohms (there is a special grounding solder joint on the right side of antenna solder joint).

[Edit this paragraph] Performance differences between RF super-regenerative and superheterodyne receivers.

Superregenerative and superheterodyne circuits have their own advantages and disadvantages. Super regenerative receiver is cheap, economical and has high receiving sensitivity, but its disadvantages are obvious, such as large frequency drift with temperature and poor anti-interference ability. The superheterodyne receiver has the advantages of stable frequency, strong anti-interference ability and stable performance with single chip microcomputer. The disadvantage is that the sensitivity is lower than that of super-regenerative receiver, and the price is much higher than that of super-regenerative receiver, and the strong short-range signal may be blocked.

[Edit this paragraph] Matters needing attention in the development of RF wireless module

The module must be modulated by signal to work normally. Common fixed code coding devices such as PT2262/2272 can be directly connected, which is very simple. Because it is a special coding chip, it has a good effect and a long transmission distance. Another important use of this module is to realize data communication with single chip microcomputer. At this time, there are some skills: 1, reasonable communication rate. The maximum transmission data rate of the data module is 9.6KBs, which is generally controlled at about 2.5 kK. Too high data rate will reduce the receiving sensitivity, increase the bit error rate, or even have no effect at all. 2. Reasonable information code format When single-chip computers and modules work, they usually define their own transmission protocols. No matter what modulation method is adopted, the format of information code to be transmitted is very important, which will directly affect the reliable sending and receiving of data. The scheme of preamble+synchronization code+data frame is recommended for the code group format, and the length of preamble should be greater than 10ms to avoid background noise, because the first bit of data received by the receiving module is easily disturbed (i.e. zero-level interference), resulting in received data errors. Therefore, CPU codec can add some random codes before data identification bits to suppress zero-order interference. Synchronization code is mainly used to distinguish preamble and data. It has certain characteristics, so that the software can identify the synchronization code through a certain algorithm to prepare for receiving data. Non-return-to-zero codes should not be used for data frames, nor should they be long 0 and long 1. Manchester code or POCSAG code is adopted. 3. When the MCU simulates 2262, the interference of the MCU to the receiving module is generally normal. However, when the MCU simulates 2272 decoding, it is usually found that the remote control distance is much shorter, because the frequency doubling of the MCU clock frequency will interfere with the receiving module. The electromagnetic interference of 5 1 series single chip microcomputer is relatively large, 205 1 series is slightly smaller, and PIC series is relatively small. We need to take some anti-interference measures to reduce interference. For example, the single chip microcomputer and the remote control receiving circuit are powered by two 5-volt power supplies, and the receiving board is powered by a single 78L05. The clock area of single chip microcomputer is far away from the receiving module, which reduces the working frequency of single chip microcomputer and adds shielding in the middle. When the receiving module interfaces with the 5 1 series single chip microcomputer, it is better to make an isolation circuit, which can better suppress the electromagnetic interference of the single chip microcomputer to the receiving module. When the receiving module is working, it usually outputs high-level pulse instead of DC level, so it can't be tested by multimeter. During debugging, a light emitting diode can be connected in series with the 3K resistor to monitor the output state of the module. When using wireless data module and special codec chips such as PT2262/PT2272, the connection is very simple. As long as it is directly connected, the transmission distance is ideal, which can generally reach more than 600 meters. If it is used in conjunction with a single chip microcomputer or microcomputer, it will be disturbed by the clock of the single chip microcomputer or microcomputer, which will obviously reduce the transmission distance, and the general practical distance is less than 200 meters.