Antennas, Antenna Cables, Wireless Products: Technical Articles
LMR-400 Coax Specifications / Characteristics: Lowest Signal Loss in Its Class
Table of Contents
LMR-400 Coax Cable Specifications
Overview & Structure
The LMR-400 is a 50-ohm, low-loss coaxial cable originally developed as a higher-performance replacement for legacy RG-8 and similar coaxial cables. The “400” designation refers to its approximate diameter class. The actual outer diameter is 0.405 inches (10.29 mm), consistent with other .400-class coaxial cables.
Low-Loss Performance
LMR-400 is widely recognized for its exceptionally low attenuation compared to traditional RG antenna cables. Its loss performance approaches that of semi-rigid and some hardline cables, while retaining flexibility.
Example attenuation comparison (typical)
- LMR-400: ~0.04 dB/ft @ 900 MHz
- RG-174: ~0.32 dB/ft @ 900 MHz
This makes LMR-400 ideal for long cable runs and high-frequency applications where signal preservation is critical.
Frequency Capability
LMR-400 performs exceptionally well above 1 GHz, making it suitable for modern RF systems operating in the UHF, L-band, and microwave ranges. While many RG-series cables can operate above 1 GHz, they suffer significantly higher losses, making LMR-400 a superior choice for higher-frequency radios and antennas.
Conductivity
The insulators are made of tinned oxygen-free copper that also comes with foil conductor tapes. These are bonded directly onto the insulator, thus providing a double-shielded coaxial cable conductor that is always effective.
Double Shielding
Due to its double shielding, the LMR should be your best option if you have a radio with 1.2 GHz or more, compared to 40 dB for RG8.
Connectors & Termination
LMR-400 supports a wide range of RF connectors, including:
- N-Type
- SMA / RP-SMA
- TNC
Connectors typically use standard hex crimp sizes, making termination reliable when proper tools are used.
Flexibility
Due to its size and shielding density, LMR-400 is less flexible than smaller cables such as LMR-200 or LMR-100. However, it offers a strong balance between performance and manageability. For installations requiring tighter bends, LMR-400-UF (Ultra-Flex) is available.
Black PVC Jacket
Just like many others in the LMR standard comes with an Ultraviolet resistant Polyethylene jacket. Combined with an aluminum alloy that is plated with an oxygen-free copper, it is highly flexible and resistant to the elements that it can last for up to 20 years of outdoor service.
LMR-400: A Deep Dive into Its Features and Applications
Coaxial or simply coax cables remain central to radio-frequency (RF) communication. With a plethora of choices available, the LMR-400 stands out for several compelling reasons. Catering especially to high-frequency applications, the LMR-400 coax cable has carved a niche for itself. This article ventures into the specifics of the LMR-400, examining its features, materials, applications, and aptitude for IoT systems.
Key Features:
- Diameter: The LMR-400 boasts a substantial diameter of approximately 10.29mm, making it robust and suitable for various applications.
- Impedance: The LMR-400 exceeds the 50 ohms impedance benchmark like many standard coax cables.
- Velocity of Propagation: It presents an impressive 85%, ensuring swift data transmission.
- Attenuation: With its low-loss characteristics, LMR-400 ensures optimal signal strength, especially over extended distances.
Construction & Materials:
At the core of the LMR-400 is its double-shielded material composition, designed for signal performance:
Center Conductor
- Solid bare copper or copper-clad aluminum (CCA)
- Designed for low resistance and stable RF performance
Dielectric
- Gas-injected foam polyethylene
- Provides an excellent velocity of propagation (~85%)
Shielding (Double-Shielded)
- Bonded aluminum foil (100% coverage)
- Tinned copper braid for mechanical strength and EMI rejection
- Shielding effectiveness typically >90 dB
Jacket
- Black UV-resistant polyethylene (PE)
- Rated for long-term outdoor exposure (up to ~20 years in typical environments)
Types:
Beyond the standard LMR-400, variations have been crafted for specific needs. There's the LMR-400-UF (Ultra Flex) for situations demanding more flexibility, and the LMR-400-DB, designed explicitly for direct burial without needing conduits. There's also the LMR-400-FR, which is fire-retardant and suitable for in-building applications.
LMR-400 Variants
To meet different installation needs, LMR-400 is available in multiple versions:
- LMR-400-UF: Increased flexibility for mobile or tight-space installations
- LMR-400-DB: Direct burial rated for underground use
- LMR-400-FR: Fire-retardant jacket for indoor and plenum-related applications
Compatible Wireless Technologies & Protocols:
LMR-400 is widely used across many RF and wireless systems:
- Cellular: 2G, 3G, 4G LTE, 5G Sub-6 GHz
- Wi-Fi: 2.4 GHz, 5 GHz, 6 GHz
- LoRa / ISM Bands
- Ham & Commercial Radio
- GPS & GNSS
- Satellite Communication
Applications & IoT Suitability
In the expanding world of IoT, connectivity is paramount. The LMR-400's low loss, high frequency, and robust build make it a front-runner:
- Common cable assembly uses include:
- IoT Infrastructure: LMR-400 ensures minimal signal loss for sprawling IoT networks, especially in urban areas where long cable runs might be necessary.
- Outdoor Sensors & Devices: The LMR-400's UV-resistant jacket suits outdoor IoT sensors, including weather stations or smart agriculture sensors.
- Smart Buildings & Campuses: Variations like the LMR-400-FR are safe for indoor applications, linking various IoT devices in smart buildings.
Why people choose LMR-400
- Lower loss than many common alternatives for longer RF cable runs
- Better performance at higher frequencies (where loss climbs quickly)
- Durable outdoor-ready options (UV-resistant jackets, etc., depending on variant)
- Wide connector availability (N-type, SMA, RP-SMA, TNC, etc.)
Common use cases
- Rooftop / outdoor antennas to indoor radios/modems
- LTE/5G routers to external MIMO antennas
- WiFi access points to remote antennas
- GPS antennas where every dB matters (especially with longer runs)
Quick comparison table (typical guidance)
(Exact loss depends on manufacturer, frequency, and build—use this as a practical buyer’s guide.)
Cable Type | Relative Loss | Flexibility | Typical “Best For” | Notes |
LMR-400 | Lowest (of these) | Medium | Longer runs, higher frequencies | Great all-around “low-loss” workhorse |
RG-8 | Higher than LMR-400 | Medium | Budget longer runs | Specs vary widely by RG-8 variant |
LMR-200 | Higher than LMR-400 | More flexible | Shorter runs, tight routing | Easier to route; more loss per foot |
Rule of thumb: if you’re pushing longer cable lengths or higher frequencies, LMR-400 usually becomes the “safe” pick.
Loss calculator example (simple and persuasive)
Example scenario: You have a 50 ft coax run at 2.4 GHz (WiFi) or ~700–2700 MHz (cellular bands).
- Find the cable loss rating at your frequency (often listed as dB per 100 ft).
- Scale it to your length:
Total Loss (dB) = (Loss per 100 ft) × (Length in ft / 100) - Add connector/adapters (a practical placeholder is ~0.1–0.3 dB per connection, depending on quality and frequency).
Mini example (generic math):
If a cable is 6.0 dB / 100 ft at your frequency, then at 50 ft:
6.0 × (50/100) = 3.0 dB loss (plus connectors)
What 3 dB means: about half your power is lost in the cable. That’s why low-loss coax matters.
When NOT to use LMR-400
LMR-400 is great—but not always the right tool:
- Very short runs (e.g., 3–10 ft): You may not see meaningful benefit vs smaller cable.
- Tight bends / highly mobile installs: LMR-400 is thicker and stiffer; LMR-200 (or another flexible low-loss option) can be easier to route cleanly.
- Weight-sensitive mounts: Thick coax can put strain on antenna connectors or mounts without strain relief.
- Ultra-long runs where loss still becomes significant: At some length/frequency combinations, it can make more sense to use remote-mounted radios, PoE, or fiber/backhaul approaches instead of “brute forcing” with coax.
- Low-frequency-only projects where cost is the priority: If you’re operating at relatively low RF frequencies and the run isn’t long, a cheaper cable may be “good enough.”
Conclusion:
When diving into the world of coaxial cables, the LMR-400's features make it a stalwart. Its meticulous design, broad-spectrum application, and suitability for IoT installations make it more than just a cable; it invests in reliable connectivity. Whether it's ensuring a steady Wi-Fi connection, setting up an extensive IoT network, or even dabbling in radio systems, the LMR-400 stands ready to deliver. As the digital age propels, equipping oneself with robust tools like the LMR-400 isn't just wise; it's essential.
FAQs
What is LMR-400 and why is it called “400”?
LMR-400 is a 50-ohm, low-loss coaxial cable designed as a higher-performance alternative to RG-8. The “400” refers to its class/diameter; actual outer diameter is ~0.405 in (10.29 mm).
How low is the signal loss on LMR-400?
It’s among the lowest in its class. Example: ~0.04 dB/ft at 900 MHz (vs. ~0.32 dB/ft for RG-174), making it ideal for longer runs.
What frequencies is LMR-400 best for?
It excels above 1 GHz (e.g., 1.2 GHz and higher), where its attenuation properties shine. It’s widely used for Wi-Fi, cellular (2G–5G), ham radio, and satellite feeds.
How is LMR-400 constructed?
- Center conductor: solid bare copper or copper-clad aluminum
- Dielectric: gas-injected foam PE (≈85% velocity of propagation)
- Shielding: bonded aluminum foil (100% coverage) + tinned copper braid (double-shielded)
- Jacket: UV-resistant black PE for outdoor durability (often rated up to ~20 years outdoors)
What variants and flexibility options exist?
LMR-400-UF (Ultra Flex) for tighter bends, LMR-400-DB for direct burial, and LMR-400-FR (fire-retardant) for in-building use. Standard LMR-400 is stiffer than LMR-200/LMR-100.
Which connectors and applications are common?
Uses standard LMR-series connectors with hex-crimp tooling; commonly built as SMA and RP-SMA assemblies (e.g., router/bridge extensions). Suited for IoT backbones, outdoor sensors, smart buildings, and general RF links where low loss is critical.