What are LMR 400 Coaxial Cables?

1 Answer
Can you answer this question?

- everything RF

Mar 28, 2023

LMR 400 Coaxial Cables are a type of cable used for carrying high frequency RF signals for wireless communication system and other antenna applications.

LMR 400 Coaxial Cable

LMR 400 Coaxial Cable Construction

The LMR 400 is a 50-ohm low-loss flexible coaxial cable with an overall diameter of 0.405 inches and a voltage rating of up to 2500 VDC. It has an internal solid copper-clad aluminum conductor (carrying the electrical signal), which is enclosed by an insulation layer made of Foam Polyethylene (Foam PE). The insulation layer is then completely enclosed by two shield layers. The first shielding layer is made of aluminum tape, and the outer shield is made of a tinned copper braid. The shields form an outer conductor, which also provides protection from electromagnetic interference (EMI). Finally, the structure is covered with an outermost layer - called a jacket - made of Polyethylene (PE).  The jacket protects the cable core from mechanical, moisture, chemical issues and environmental factors. 

The LMR 400 cable exhibits capacitance of approximately 23.9 pF/ft (78.4 pF/m) and signal attenuation of around 3.9 dB/100ft at 900 MHz (signal attenuation of the cable depending on the frequency) and has a velocity of propagation of 84%. It has a center conductor measuring 0.108 inches (2.74 mm) in diameter and an insulation layer measuring 0.285 inches (7.24 mm) in diameter. The double shielding structure of the LMR 400 coaxial cable offers RF shielding of more than 90 dB. 

The LMR 400 cable has the lowest loss of any RG8/RG213 type cable. The LMR 400 cable can be used to replace the RG-8 cable, and it has a few overlapping characteristics with the RG213 cable. These cables are similar products; hence they are compared. The high-performance, flexible, low-loss LMR 400 cable can be used virtually anywhere, either indoors or outdoors. The LMR 400 cable is ideal for use in drop-in replacement of RG-8/9913 air- dielectric type cable, jumper assemblies in wireless communication systems, short antenna feeder runs, and any application (e.g., WLL, GPS) requiring an easily routed, low loss RF cable.

Key Specifications of LMR 400 Coaxial Cables


Typical Value

Overall Diameter (inch)


Characteristic Impedance (Zo)

50 ohms

Maximum Voltage Rating (VDC)

2500 V

Cable Capacitance (pF/ft)


Inductance (µH/ft)


Attenuation (dB/100 ft, @ 900 MHz)



Foam Polyethylene (Foam PE)

Minimum Bend Radius (inch), installation


Click here to view other RF coaxial cables on everything RF.