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Introduction to LMR 400 Coaxial Cables

Jun 30, 2025

LMR 400 coaxial cables are specifically designed as high-frequency radio frequency (RF) signal transmission lines for wireless communication systems and other antenna applications.

Overview of LMR 400 Coaxial Cables

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LMR 400 is a 50-ohm low-loss flexible coaxial cable with an overall diameter of 0.405 inches and a rated voltage of up to 2500 VDC. It features a solid copper-clad aluminum conductor as the core for signal transmission, enclosed by a layer of foam polyethylene (Foam PE) insulation. This insulation layer is then completely wrapped by two shielding layers: the first layer is made of aluminum tape, and the outer layer is a braided shielding of tinned copper. These two shielding layers not only constitute the outer conductor but also provide excellent electromagnetic interference (EMI) protection. The outermost layer of the cable is a polyethylene (PE) jacket, which effectively protects the cable core from mechanical damage, moisture, chemicals, and environmental factors.

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Key Performance Parameters

‌Overall Diameter‌: 0.405 inches
‌Characteristic Impedance‌: 50 ohms
‌Rated Voltage‌: 2500 VDC
‌Cable Capacitance‌: Approximately 23.9 pF/foot (78.4 pF/meter)
‌Inductance‌: 0.060 µH/foot
‌Attenuation‌: Approximately 3.9 dB/100 feet at 900 MHz (cable attenuation varies with frequency)
‌Insulation Material‌: Foam Polyethylene (Foam PE)
‌Minimum Bend Radius (for Installation)‌: 1.0 inch

LMR 400 cables exhibit a propagation velocity of approximately 84%, with a center conductor diameter of 0.108 inches (2.74 mm) and an insulation layer diameter of 0.285 inches (7.24 mm). Its unique double-shielding structure provides RF shielding effectiveness of over 90 dB.

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Application Advantages and Scenarios

LMR 400 coaxial cables, with their high performance, flexibility, and low loss characteristics, are ideal for numerous applications. Compared to RG8/RG213-type cables, LMR 400 has the lowest loss. It can serve as a replacement for RG-8 cables and overlaps with RG213 cables in some characteristics. LMR 400 cables can be used both indoors and outdoors, especially suitable for the following scenarios:

Direct replacement for RG-8/9913 air-dielectric type cables
Jumper assemblies in wireless communication systems
Short antenna feeder runs
Any application requiring easily routed, low-loss RF cables (such as wireless local loop (WLL), GPS, etc.)