Video Surveillance via Coaxial Cable
Coaxial cables are widely used in video surveillance due to their simplicity and affordability. However, they are prone to signal attenuation and interference, which must be addressed for optimal performance.
Key Considerations
- Signal-to-Noise Ratio (SNR): A minimum SNR of 40 dB is recommended for clear images. At 20 dB, image quality significantly degrades.
- Electromagnetic Interference (EMI): Coaxial cables are vulnerable to EMI, especially in areas with fluctuating noise levels caused by electrical equipment.
For short distances (up to 300 feet), coaxial cables typically perform well. However, in challenging environments, interference may disrupt signals even at 100-150 feet.
Choosing the Right Coaxial Cable
Low Attenuation:
- Select cables with minimal signal loss, though specifications are often provided for higher frequencies (e.g., 100 MHz), which may not fully reflect performance in the 50 Hz–6 MHz range used for video signals.
Key Parameters:
- Impedance: Use 75-ohm coaxial cables for video surveillance.
- Diameter: Larger diameters reduce signal loss.
- Material: Both the core and shielding should be copper for optimal conductivity.
Popular cables include RG-59, RK-75-2, and RK-75-4, which are widely recognized in the surveillance industry.
Enhancing Signal Quality and Transmission Range
While coaxial cables are cost-effective, additional equipment can extend their range and improve performance:
Signal Grounding:
- Use proper signal grounding with a grounding rod at least 8-10 feet deep, avoiding proximity to power circuits. Ground the shielding at only one end (transmitter or receiver).
Signal Amplifiers:
- Amplifiers enhance the signal-to-noise ratio at the receiver end, resulting in better image quality.
Matching Transformers:
- Provide galvanic isolation, reducing noise levels and improving signal integrity.
RF Modulation:
- Convert the video signal into a high-frequency television signal for transmission, then revert it back at the receiver.
Tips for Installation
- Place power supplies as close to cameras as possible to minimize noise on the power line.
- Use high-quality connectors and ensure secure connections to prevent signal degradation.
- Test the system with a sample setup before full installation to evaluate signal performance under real conditions.
Coaxial cables remain a reliable and economical choice for video surveillance, especially for smaller-scale installations. By selecting the right equipment and employing advanced techniques, you can ensure clear, stable video transmission even in challenging environments.