**1. Video Baseband Transmission:**
The most traditional method of television monitoring transmission involves sending 0 to 6 MHz video baseband signals without any processing, directly through coaxial cables in an unbalanced configuration. This technique has been widely used for many years and is known for its simplicity.
**Advantages:**
This method offers minimal signal loss over short distances, low cost, and a stable system. It's ideal for small-scale systems where the distance between devices is limited.
**Disadvantages:**
However, it has several limitations. The transmission distance is very short, and after about 300 meters, high-frequency components start to degrade significantly, leading to poor image quality. The wiring can be complex and difficult to maintain, with limited scalability. It’s also not suitable for large installations. Additionally, using non-standard cables can cause issues like video interference, character jumping, or screen distortion when using matrix switches or video splitters. Ensuring proper cabling standards is crucial to avoid such problems.
**2. Fiber Optic Transmission:**
Fiber optic transmission is one of the best solutions for long-distance monitoring, especially when dealing with tens or even hundreds of kilometers. Analog and digital optical transceivers convert video and control signals into laser light for transmission through optical fibers.
**Advantages:**
It provides a long transmission range with low signal attenuation and excellent resistance to electromagnetic interference. Standard optical transceivers can transmit up to 20 kilometers, and using 8-channel transceivers is often the most cost-effective solution. While fiber optics have become more affordable, they still require specialized equipment and skilled technicians for installation and maintenance.
**Disadvantages:**
For shorter distances, fiber optics may not be economical. Installation and maintenance require professional skills, making upgrades and expansions more challenging. Some engineers might cut corners by directly connecting fiber pigtails without using proper jumpers or flanges, which can lead to serious issues during future maintenance.
**3. Network Transmission:**
To address long-distance and widely dispersed monitoring needs, network transmission uses compression formats like MPEG-2/4 or H.264 to send video signals over IP networks.
**Advantages:**
With network video servers, monitoring signals can be uploaded and accessed remotely via internet-based software. This allows for flexible and scalable monitoring solutions.
**Disadvantages:**
However, network transmission is limited by bandwidth and speed, resulting in lower image quality and frame rates. Delays and lag are common, making real-time monitoring difficult. Despite these challenges, I remain optimistic about the future of network-based monitoring as technology continues to improve.
**4. Twisted-Pair Transmission (Balanced Transmission):**
This method converts the unbalanced 75-ohm video signal into a balanced signal for transmission over twisted-pair cables. It’s commonly used for short-range monitoring, typically up to 1 km.
**Advantages:**
It offers easy installation, low cost, and strong resistance to common-mode interference, making it suitable for environments with electrical noise.
**Disadvantages:**
But it has limitations. It can only transmit one video signal per pair, and is not ideal for large or medium-sized systems. The twisted-pair cables are also prone to aging and degradation, making them unsuitable for field applications. High-frequency components are heavily attenuated, leading to color loss and reduced image quality.
**5. Coaxial Cable Transmission:**
This method uses technologies like AM modulation and FSK data modulation to combine multiple video, audio, control, and alarm signals into a single coaxial cable for two-way transmission. It's similar to the technology used in cable TV networks and is a mature, practical solution for closed-circuit television systems.
**Advantages:**
It makes full use of the coaxial cable's capacity, allowing up to 20 channels of audio, video, and control signals to be transmitted simultaneously on the same line. This reduces material and construction costs significantly. Frequency division multiplexing helps overcome the challenges of long-distance transmission and complex wiring. The RF transmission mode minimizes signal loss, ensuring image quality meets or exceeds national standards. The 75Ω unbalanced transmission also provides strong resistance to interference, maintaining image quality even in harsh environments.
**Disadvantages:**
However, this technology requires cross-industry collaboration and expertise, especially in RF design and system integration. Many aspects depend on experience, and system debugging often requires professional instruments and advanced technical knowledge.
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