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How to Choose Coaxial Cable for Outdoor VSAT Installations
Coaxial Cable for Outdoor VSAT Installations: LMR, RG, and Burial-Rated Options
Published by Bravosatcom · VSAT Engineering Series
The cable you run between your VSAT modem, BUC, and LNB — the IFL (Inter-Facility Link) cable — is the only part of the satellite system that you physically design and install from scratch. Everything else (the BUC, LNB, modem, antenna) arrives with published specifications. The cable is where installers routinely make mistakes that cut link margin, shorten equipment life, or result in a failed commissioning.
This guide covers coaxial cable selection for outdoor VSAT installations: which cable types work, how to calculate the loss budget for your run length, and which cable is right for your specific installation environment.
Why Cable Choice Matters for VSAT
In a VSAT installation, the IFL cable runs between:
- BUC to outdoor unit (ODU): The transmit path at L-band (950–1450 MHz or 950–2150 MHz)
- LNB to indoor unit (IDU): The receive path, also at L-band
- Reference signal: 10 MHz reference from the modem to the BUC (in some installations)
Every meter of cable adds attenuation. At L-band frequencies (950–2150 MHz), coaxial cable losses are significant. A 50m run of the wrong cable can add 5–8 dB of insertion loss — consuming most of your uplink power budget before the signal even reaches the BUC. This directly reduces your EIRP and can prevent the link from closing.
Cable also degrades over time, especially outdoors. Poor UV resistance, water ingress at connectors, and thermal cycling cause additional losses that worsen over years. Specifying the right cable at installation avoids expensive cable replacements and intermittent faults years later.
The Main Cable Types for VSAT IFL
LMR-400 (Times Microwave)
LMR-400 is the industry standard for VSAT IFL cable. It offers a good balance of low attenuation, manageable flexibility, and proven outdoor durability. Key specs:
- Impedance: 50 ohm
- Outer diameter: 10.3 mm (0.405 in)
- Attenuation at 1.5 GHz: approximately 5.1 dB/100 ft (16.7 dB/100m)
- Attenuation at 2.1 GHz: approximately 6.5 dB/100 ft (21.3 dB/100m)
- Velocity factor: 85%
- Temperature range: –40°C to +85°C
- UV-resistant black PE jacket
For most VSAT installations with IFL runs up to 30m, LMR-400 is the default choice. Direct burial variant (LMR-400-DB) adds a flood-filled jacket for underground runs.
LMR-600 (Times Microwave)
LMR-600 is a larger, lower-loss cable used when runs exceed 25–30m or when the installation is at Ka-band (which has tighter EIRP margins). Specs:
- Outer diameter: 15.8 mm (0.590 in)
- Attenuation at 1.5 GHz: approximately 3.3 dB/100 ft (10.8 dB/100m)
- Attenuation at 2.1 GHz: approximately 4.2 dB/100 ft (13.8 dB/100m)
- Velocity factor: 87%
- Minimum bend radius: 38 mm
LMR-600 saves approximately 2 dB over LMR-400 on a 30m run, which is significant for Ka-band links or installations near the edge of the satellite beam. The trade-off is that it is stiffer, heavier, and more expensive to terminate correctly.
LMR-240
LMR-240 is a smaller diameter cable (6.1 mm) with higher attenuation. It is only suitable for short IFL runs under 10–15m where physical flexibility or tight bends are a priority (e.g., within equipment racks or cable ducts). Do not use LMR-240 for primary IFL runs in a professional VSAT installation.
RG-6 and RG-11
RG-6 (75 ohm) is a consumer-grade cable designed for satellite television. It is not suitable for professional VSAT IFL use for two reasons: it is 75 ohm (VSAT equipment uses 50 ohm), and its attenuation at 2 GHz is comparable to LMR-240. RG-11 (also 75 ohm) offers lower attenuation but the same impedance mismatch problem. Neither is acceptable for a properly designed VSAT installation.
Attenuation Comparison at VSAT Frequencies
The chart below compares the four main cable types at the three key L-band frequencies used in VSAT IFL applications.
For a 30m (approximately 100 ft) IFL run at a Ka-band site operating at 2100 MHz, the cable loss difference between LMR-400 (6.7 dB) and LMR-600 (4.4 dB) is 2.3 dB. Given that Ka-band links typically run with tight margins of 4–8 dB, saving 2.3 dB by upgrading cable is often more cost-effective than increasing BUC power.
Cable Structure and Quality
The quality differences that matter for VSAT:
- Dielectric material: Foam PE (also called foam polyethylene) is lighter and has lower loss than solid PE. All LMR and quality VSAT cables use foam PE. Solid PE dielectrics have attenuation 15–20% higher and should be rejected.
- Shield coverage: Quality cables use a composite shield: both a foil layer (100% coverage) and a braid (typically 88–96% coverage). This provides >40 dB isolation, preventing external interference from reaching the receive chain. Braid-only shields or thin foil-only shields should not be used.
- Connector termination: LMR cable uses specific crimp dies and compression tools. Incorrectly 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” alt=”LMR-400 coaxial cable cross section diagram VSAT IFL” loading=”lazy”/>
Figure 2 — LMR-400 cable cross-section. The bonded foil and braid shield combination provides >40 dB isolation. The foam PE dielectric gives 85% velocity factor, reducing electrical length compared to solid PE cables. The four layers of a quality IFL cable each serve a specific purpose. The center conductor carries the RF signal; the foam dielectric determines the velocity factor and contributes to the cable’s low loss; the shield provides isolation from external interference and prevents signal leakage (important for adjacent-channel interference in dense installations); and the outer jacket protects against UV, moisture, and physical abrasion.
Counterfeit or substandard IFL cables use aluminium center conductors, lower braid coverage (<80%), or UV-vulnerable jackets. These failures occur 1–3 years into installation rather than immediately, making them hard to diagnose. Always source IFL cable from a verified distributor with a certificate of conformance.
Selecting Cable by Installation Environment
Figure 3 — Cable selection matrix by scenario and satellite band. For Ka-band, always select at minimum LMR-400; for runs over 30m on Ka-band, upgrade to LMR-600. Direct Burial
Standard IFL cable jackets are designed for above-ground or conduit use. For direct burial, specify the -DB variant (e.g., LMR-400-DB), which adds a flood compound inside the outer jacket that seals against water ingress even if the jacket is cut or abraded underground.
Aerial Installation (Self-Supported)
For aerial runs between buildings or towers, use a messenger-strand version or route the cable along a steel messenger wire. Standard LMR cable is not designed to support its own weight over long spans. UV resistance is critical — verify the jacket rating; some aftermarket cables use jackets that crack within 18 months in desert climates.
Extreme Temperature Environments
Gulf/MENA region installations must handle ambient temperatures of 45–55°C at the cable. LMR-400 is rated to +85°C, which is sufficient, but cables routed on south-facing metal surfaces can exceed this in peak summer. Route cables in shaded conduit or use a cable sleeve where direct solar exposure is unavoidable.
Connectors and Termination
The connector is always the weakest point in an IFL cable run. Use N-type connectors for LMR-400 and LMR-600 — they are weatherproof, low-loss, and rated for outdoor use. SMA connectors are too small for LMR-400 and not appropriate for outdoor IFL use. Crimp-type connectors are acceptable for LMR-240 in short indoor runs; solder-and-clamp or compression connectors are preferred for LMR-400 in outdoor applications.
Seal all outdoor connectors with self-amalgamating tape or weatherproof boots after installation. A single water-infiltrated connector adds 2–5 dB of insertion loss and corrodes the braid within months.
Frequently Asked Questions
Can I use RG-58 or RG-59 for a short VSAT IFL run?
No. RG-58 is 50-ohm but has very high attenuation at L-band (over 15 dB/100 ft at 1.5 GHz) and is not UV-resistant. RG-59 is 75-ohm and causes an impedance mismatch. Neither is suitable for professional VSAT IFL applications, even for short runs.
How do I calculate maximum IFL cable length?
Calculate the total allowed cable loss from your link budget (typically the operator specifies a maximum IFL loss, or you can derive it from the BUC EIRP requirement). Divide the allowed loss by the cable’s attenuation per unit length at your operating frequency. For example: 6 dB allowed loss, LMR-400 at 1.5 GHz = 5.1 dB/100 ft. Maximum run = (6 / 5.1) * 100 = approximately 117 ft (36m). Always subtract connector losses (0.2–0.5 dB per connector pair) from the allowed budget first.
What is the difference between LMR-400 and LMR-400-UF (UltraFlex)?
LMR-400-UF uses a stranded center conductor instead of a solid one, making it more flexible and less prone to kinking during installation. Attenuation is slightly higher than standard LMR-400 (by approximately 0.2–0.4 dB/100 ft at L-band). Use LMR-400-UF where the cable must be routed around tight bends or will be flexed regularly; use standard LMR-400 for fixed runs where low loss is the priority.
Does cable length affect the power supply to the LNB?
Yes. The LNB is powered by DC voltage supplied over the coax from the modem or LNB power supply (typically 13V or 18V for Ku-band polarization switching). Longer cable runs cause a voltage drop due to the DC resistance of the center conductor. For LMR-400, the DC resistance is approximately 4.3 ohm/100m. On a 50m run, this adds 0.43 ohm (plus return path). At 200mA LNB current, that is 86mV drop — usually acceptable. For very long runs (>80m) verify that the LNB receives adequate voltage at the operating current draw.
Is there a way to extend the IFL run without upgrading to LMR-600?
Yes — using an in-line amplifier (IFL amplifier) can compensate for cable loss on long runs, but it adds cost, a potential failure point, and requires a power source at the midpoint. A simpler option is to upgrade to LMR-600 for the full run. If the modem supports Automatic Level Control (ALC) or Uplink Power Control (UPC), some additional loss can be compensated dynamically, but this consumes your fade margin. The cleanest solution is to run correctly sized cable from the start.
Need IFL Cable for Your VSAT Installation?
Bravosatcom supplies Times Microwave LMR-400, LMR-600, and LMR-400-DB cable cut to length, with matching N-type connectors, for VSAT installers across the GCC and MENA region.