Adaptation to Wireless Intercom System Engineering
I. Basic Selection of RF Coaxial Cable (50 Ω Impedance)
Wireless intercom UHF 400～470MHz systems uniformly use 50 Ω RF coaxial cable. The use of commonly used 75 Ω cables for surveillance is strictly prohibited. Commonly Used Cable Type Classifications in Engineering Projects:
50-5 (50-5)
Suitable for: Short patch cords inside computer rooms, indoor distribution branch lines on floors, flexible and easy to bend cabling.
Limitations: Loss is too high over 30 meters; prohibited as long outdoor trunk lines on rooftops.
1/2-inch Corrugated Feeder (HCAAYZ-50-12)
Suitable for: Rooftop trunk lines, long-distance indoor distribution trunk lines in basements, balancing loss and ease of construction.
Features: Low loss, high mechanical strength; preferred for trunk lines in large and medium-sized hotel projects.
7/8-inch Corrugated Feeder (HCAAYZ-50-22)
Suitable for: Ultra-long-distance trunk links, large-scale simultaneous broadcast systems, long-distance campus coverage.
Disadvantages: High rigidity, difficult construction, high cost; rarely used throughout the entire line in ordinary hotels.
Loss Reference (450MHz band, loss per 100 meters):
50-5 Feeder: ≈ 7.8 dB/100m
1/2-inch Feeder: ≈ 4.6 dB/100m dB/100m
7/8 Feeder Tube: ≈ 2.6 dB/100m
II. RF Connector Compatibility Requirements
Different cables must be matched with dedicated connectors.
50-5 Feeder → 50-5 dedicated N connector; 1/2 Feeder Tube → 1/2 Feeder screw-on N connector; 7/8 Feeder → DIN7/16 connector. Mixing is strictly prohibited.
During connector processing, the inner conductor and foam insulation layer of the cable must not be scratched; metal debris must be thoroughly cleaned to prevent short circuits and damage to the repeater amplifier.
All outdoor connectors must undergo a multi-layer waterproofing process (waterproof silicone grease + high-voltage self-adhesive tape + outer protective tape).
III. Testing and Acceptance Standards (with Supporting Testing Plan)
Visual Inspection: The outer sheath is undamaged, without flattening or twisting, and securely fixed; the joints are waterproof and intact.
Standing Wave Ratio (SWR) Test
The SWR of the entire coaxial link ≤ 1.5 is acceptable.
Segmented Testing to Locate Faults: Differentiate between cable defects and faulty joint construction.
Continuity Test: No short circuits between inner and outer conductors.
Retain test records after completion, highlighting test data for the main feeder cable.
IV. Common Faults (Cable-Related)
Cable compression or hard bending → Local impedance changes, excessive SWR, intermittent signal at distant ends;
Aging and cracking of outdoor cable sheath leading to water ingress → Worsened blind spots in rainy weather;
Incorrect use of 50-5 feeder cable in long lines → Significant RF loss, weak uplink/downlink signals in basements and distant floors;
Joints without drip traps, rainwater seepage → Joint corrosion, intermittent communication failures.
Summary
The entire RF coaxial cable wireless intercom antenna system utilizes 50Ω RF coaxial cable, with cable selection tiered according to link length: 50-5 flexible feeders are used for indoor branch lines, 1/2-inch corrugated feeders are used for outdoor trunk lines and long-distance indoor distribution main lines, and 7/8 inch feeder conduits can be used for extra-long trunk lines. The cables feature low attenuation and low VSWR characteristics, operating in the 400–470MHz frequency band. Construction strictly adheres to minimum bending radius specifications, with proper installation of fixed supports to avoid damage from compression or hard bending. Outdoor cables feature weather-resistant and UV-resistant outer sheaths and are waterproofed with drip bends. Cables and RF connectors are matched one-to-one, with strict control over intermediate connection points to reduce RF loss. VSWR testing is conducted in sections after installation to ensure stable intercom signal transmission throughout the project area.
