RS-485 is a communication standard that uses balanced transmission and differential reception to enable reliable data transfer. At the transmitting end, the TTL-level signal from the serial port is converted into a differential signal (A and B), which is then transmitted through twisted-pair cables. Upon reaching the receiving end, this differential signal is converted back into a TTL-level signal. Because of the use of twisted pairs and differential signaling, RS-485 is highly resistant to common-mode interference. Additionally, the bus transceivers are sensitive enough to detect voltages as low as 200 mV, allowing signals to be recovered over distances exceeding one kilometer. The maximum communication distance for RS-485 is approximately 1219 meters, with a maximum data rate of 10 Mbps. However, the transmission speed and distance have an inverse relationship—lower speeds allow for longer distances. At 100 kbps, the maximum distance can be achieved, but for longer runs, a 485 repeater may be necessary. RS-485 operates in half-duplex mode and supports multi-point communication. The typical network topology is a daisy-chain or bus structure, where devices are connected in series. Ring or star topologies are not supported unless a 485 repeater or hub is used. In general, the bus can support up to 32 nodes, though with specialized 485 chips, this number can increase to 128 or even 256 nodes, with some systems supporting up to 400 nodes. **RS-485 Wiring Specifications** Due to its simple wiring and high reliability, the RS-485 bus is widely used in applications such as video surveillance, access control systems, and building alarm systems. However, improper installation practices often lead to issues due to misconceptions about the wiring process. Here are some key points to consider: 1. **Signal lines should not be run alongside power lines.** In real-world installations, it's common to bundle 485 signal lines with power lines for convenience. However, this can cause electromagnetic interference, leading to unstable communication. It’s best to keep them separate whenever possible. 2. **Shielded or unshielded twisted pair cables can both be used.** Since RS-485 uses differential signaling, the voltage difference between the A and B lines is what carries the signal. Twisted pair cables help reduce external interference by ensuring that both lines experience the same noise, maintaining the integrity of the signal. Shielded cables offer additional protection against external interference. 3. **Use proper cable types.** It is recommended to use shielded twisted pair cables designed specifically for RS-485 rather than standard Ethernet cables. Some manufacturers may use lower-quality materials, such as alloys instead of copper, which can lead to poor conductivity and breakage. Always check the cross-section of the wire—copper will appear reddish, while alloy wires are typically white. 4. **Avoid arbitrary star or tree configurations.** While it's tempting to use star or tree wiring for convenience, this can cause signal reflections and bus instability. If you need to use these structures, always do so through a 485 hub or repeater to maintain signal integrity. 5. **Grounding is essential.** Proper grounding is crucial for reducing common-mode interference. The entire RS-485 bus should be grounded at a single point to ensure consistent ground potential across the system. Multiple grounding points can create ground loops, which can introduce noise and degrade performance. **Correct Wiring Method for RS-485 Communication** The ideal wiring configuration for RS-485 is using twisted pair cables. For half-duplex communication, a single pair of twisted wires is sufficient, providing excellent noise immunity. In full-duplex mode, two pairs are used—one for transmitting and one for receiving. In practical applications, outdoor-rated twisted-pair cables are often used to protect the signal from environmental factors. While some engineers opt for RVV cables, they tend to offer less interference resistance compared to shielded options like RVVP. However, adding shielding increases capacitance, which can affect signal quality and require a reduction in baud rate. The baud rate should be adjusted based on the length of the cable. Longer lines require slower baud rates to maintain signal integrity. Whenever possible, use a bus topology rather than star or tree configurations, and keep branch lines as short as possible. Avoid connecting unused devices to the bus, as they can introduce unnecessary noise. If signal strength is weak at the far end of the bus, a 120-ohm resistor can be added across the signal lines to improve termination. Do not add intermediate devices unless absolutely necessary, as they can increase signal loss and reduce the number of devices that can be connected. Different RS-485 chips may have varying load capabilities, making it difficult to determine the exact number of devices that can be connected. Always refer to the manufacturer’s specifications for guidance. In full-duplex mode, the host’s transmit line connects to the slave’s receive line, and vice versa. In half-duplex mode, the connections are made using positive and negative polarity.

3G 4G LTE 5G Antenna

The Description of 3G 4G LTE/5G Antenna
 
2G base station: GSM: 900/1800MHz; CDMA: 800 MHZ;
 
3G base station: CDMA2000&WCDMA: 2100MHz; Td-scdma: 1880-1920201 0 0-2025232-2370 MHZ;
 
4G base station: TDD-LTE: 2320-2370,2570-2620MHz;
 
This paper discusses the key technologies in 3G/4G/5G (third generation/fourth generation/fifth generation) communication systems, and then discusses the differences in the antenna technologies adopted by them. After reading and studying a large number of papers on the key technologies of 3G/4G/5G communication system, here I make some analysis and summary of my own. With the rapid development of science and technology, mobile communication technology has undergone profound changes, from 1G to 2G, to 3G, and then to 4G and 5G. On December 4, 2013, the fourth generation of mobile communication 4G technology was officially operated in the Chinese market, which means that China's mobile communication industry has entered the 4G era. At this time, research institutes in various countries and world-renowned enterprises engaged in communication technology research have entered the research and development of the new generation of mobile communications, namely 5G (fifth generation mobile communication system). No matter which generation of communication system, the research technology is to analyze the characteristics of wireless communication channel to overcome the noise interference. A lot of researchers are now looking at Massive MIMO technology. How is it different from the antenna technology used in 3G/4G communication systems? Will it become the core technology of the next generation of wireless communications? 1 Key technologies of 3G/4G/5G Communication System 1.1 Key technologies of 3G Communication System Since the early 1990s, the mobile communication industry began to actively study the standards and technologies of the third generation of mobile communication. In January 2009, China's Ministry of Industry and Information Technology issued 3G licenses to China Mobile, China Telecom and China Unicom, indicating that China entered the ERA of 3G mobile communications. The third generation mobile communication system mainly includes WCDMA, CD-MA2000 and TD-SCDMA. Its key technologies include: A. Rake receiving technology; B. Channel coding and decoding technology; C. Power control technology; D. Multi-user detection technology; E. Smart antenna; F. Software radio. 1.2 Key technologies of 4G Communication System In December 2013, China officially entered the era of 4G (fourth generation mobile communication system) communication network. In 4G mobile communication system, OFDM(Orthogonal frequency Division multiplexing) technology is adopted. OFDM technology is due to its spectrum utilization
 
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It is widely regarded as high rate of 2 and good anti-multipath fading performance. In the future, RESEARCH related to OFDM technology will also be carried out in 5G communication networks. The main key technologies of 4G communication system include: a. OFDM technology; B. MIMO technology; C. Multi-user detection technology; D. Software radio; E. Smart antenna technology; F. IPv6 technology. China's Ministry of Industry and Information Technology has just issued 4G licenses to the three major operators, and they are still deploying their networks on a large scale with a small number of users. At this time, China Mobile said it will start the RESEARCH and development of 5G communication system. Analysts pointed out that the three major operators are participating in THE RESEARCH and development of 5G, one is to keep up with the changes of The Times, and the other is that the demand is faster than the technology development. Li Zhengmao, vice-president of China Mobile, said at the 2014 MWC in Barcelona: "China Mobile will fully support the development of 5G projects, hoping to lead the industry in THE development of 5G technology and the setting of technical standards." With the deepening of mobile communication technology research, the key support technologies of 5G will be gradually defined and enter the substantive standardization research and formulation stage in the next few years. The jury is still out on what core technologies will be used in the future. However, I have compiled a list of nine key technologies that have been the focus of discussion in various high-end mobile forums. A. Large-scale MIMO technology; B. Filter bank based multi-carrier technology; C. Full duplex technology; D. Ultra-dense heterogeneous network technology; E. Self-organizing network technology; F. Use of high frequency band; G. Software-defined wireless networks; H. Wireless access technology: (1) BDMA (Beam Split multiple Access technology)
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3 (2) NOMA (Non-orthogonal multiple Access technology) i. D2D (device-to-device) communication. Figure 1 is the layout of Massive MIMO antennas in 5G communication networks. I am studying Massive MIMO technology in my lab. Figure 1 shows users communicating with each other centered on a large-scale antenna. The performance of wireless communication systems is mainly restricted by mobile wireless channels. Wireless channel is very complex, and its modeling has always been a difficult point in system design. Generally, statistics are made according to the measured values of communication systems in specific frequency bands. Wireless fading channel is divided into large scale fading channel model and small scale fading channel model. The so-called large-scale fading model describes the field intensity variation over a long distance (hundreds or thousands of meters) between the transmitter and receiver, and reflects the rule that the received signal power changes with the distance caused by path loss and shadow effect. A small scale fading model describes the rapid fluctuations of the received field intensity over a short distance or time. The large scale fading channel model is caused by the influence of the surface contour (such as mountains, forests, buildings, etc.) between the receiver and the source. The small-scale fading channel model is caused by the multipath effect and doppler effect. If there are a large number of reflected paths but no LOS (direct signal) signal component, the small-scale fading is called Rayleigh fading, and the envelope of the received signal is described statistically by the Rayleigh probability density function. If LOS is present, the envelope is subject to Rician distribution. Multipath effect phenomena cause flat fading and frequency selective fading.
 
 

      The Picture of 3G 4G LTE/5G Antenna

5G antenna

 

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September 25, 2025