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Coaxial Cable for Two-Way Radio Base Stations: LMR-240 vs LMR-400 vs LMR-600
Coaxial Cable for Two-Way Radio Base Stations: LMR-240 vs LMR-400 vs LMR-600
Published by Bravosatcom · Cable Engineering Series
A two-way radio system is only as good as the cable between the radio and the antenna. Connect a 25 W radio to its antenna with thin, lossy coax and a large share of that power is turned into heat inside the cable before it ever reaches the antenna. The same loss then works against you on receive.
This guide compares LMR-240, LMR-400 and LMR-600 at VHF and UHF using Times Microwave published attenuation figures, shows how much power each one actually delivers on a typical run, and gives a simple way to choose the right cable for a base station or repeater site. For the basics of how loss is measured, see our guide to cable attenuation.
Why Feedline Loss Matters More Than Radio Power
Coax loss is measured in decibels, and decibels add up quickly: every 3 dB of loss removes half of the power. Loss is also symmetrical. Whatever the cable takes from your transmitter on the way out, it takes from the incoming signal on the way in, so a lossy feedline shrinks your coverage in both directions.
That second point is why a more powerful radio is rarely the right fix. A base station can be upgraded from 25 W to 50 W, but the handheld talking back to it cannot, and the handheld’s signal still has to survive the same cable before it reaches the base receiver. Reducing feedline loss improves both directions at once. Extra transmit power improves only one.
Published Attenuation: LMR-240, LMR-400 and LMR-600
| Cable | 150 MHz (VHF) | 450 MHz (UHF) | Single bend | Best suited to |
|---|---|---|---|---|
| LMR-240 | 9.9 dB/100 m | 17.3 dB/100 m | 19.0 mm | Short jumpers and runs up to about 10 m |
| LMR-400 | 5.0 dB/100 m | 8.9 dB/100 m | 25.4 mm | Standard base station feedline |
| LMR-600 | 3.2 dB/100 m | 5.6 dB/100 m | 38.1 mm | Long runs, tower sites, repeaters |
Values are Times Microwave published figures at 25 °C, converted from dB per 100 ft. Always check the current datasheet before specifying a critical link. The full LMR range is covered in our Times Microwave LMR series guide.
What Each Run Length Costs You
| Run length | LMR-240 | LMR-400 | LMR-600 |
|---|---|---|---|
| 10 m | 1.0 / 1.7 dB | 0.5 / 0.9 dB | 0.3 / 0.6 dB |
| 25 m | 2.5 / 4.3 dB | 1.3 / 2.2 dB | 0.8 / 1.4 dB |
| 50 m | 5.0 / 8.7 dB | 2.5 / 4.5 dB | 1.6 / 2.8 dB |
Each cell shows VHF (150 MHz) / UHF (450 MHz) loss. These figures cover the cable only. Allow an extra fraction of a dB for each connector pair, jumper and surge protector in the path.
How Much Power Actually Reaches the Antenna
Take a 25 W UHF radio, the power class of a mobile such as the Motorola DM1400 UHF 25W, feeding an antenna through 25 m of cable at 450 MHz:
| Cable | Loss over 25 m | Power delivered | Power at the antenna |
|---|---|---|---|
| LMR-240 | 4.3 dB | 37% | about 9 W |
| LMR-400 | 2.2 dB | 60% | about 15 W |
| LMR-600 | 1.4 dB | 72% | about 18 W |
Changing only the cable from LMR-240 to LMR-400 puts roughly 60% more power on the antenna, and improves receive sensitivity by the same 2.1 dB. No radio upgrade at this price point delivers both.
How Long Can the Run Be?
A common design guideline is to keep feedline loss at or below about 3 dB, which is half the power. Many sites aim lower. Figure 2 shows the longest run that stays within 3 dB for each cable.
Choosing the Cable
- Up to about 10 m: LMR-240 is acceptable, especially at VHF, and its tighter bend radius helps inside cramped cabinets.
- 10 to 35 m: LMR-400 is the standard choice and suits most rooftop base stations and small repeater sites.
- 35 to 55 m at UHF (or 60 to 95 m at VHF): LMR-600.
- Beyond that: do not just keep adding cable. Move the radio or repeater closer to the antenna, or step up to a larger low-loss feedline.
Where a route is genuinely tight, LMR-400-UF (UltraFlex) trades a little extra loss for a smaller bend radius. See our guide to minimum bend radius before pulling any run.
Connectors and Installation Notes
- Match the connector to the cable. An N-type connector for LMR-400 and one for LMR-600 are different parts. The wrong body gives a poor crimp and intermittent contact. For LMR-400 see the NJ-7 N-type plug.
- Use N-type or 7/16 DIN at UHF. The UHF (PL-259) connector is fine for HF and VHF, but it is not constant-impedance, so avoid it at UHF. For high-power repeaters see 7/16 DIN vs N-Type.
- Weatherproof every outdoor connector with self-amalgamating tape and a UV-resistant overwrap. Water ingress is the most common reason a feedline gets worse over time.
- Buy genuine cable. Generic coax can lose noticeably more than the datasheet figure. See LMR-400 original vs generic.
Still deciding on the radios themselves? Our Motorola vs Kenwood vs ICOM comparison covers brand choice for UAE sites.
Frequently Asked Questions
Can I use LMR-240 for a base station antenna?
Yes, if the run is short. At 450 MHz it loses about 1.7 dB over 10 m, which is acceptable. By 25 m it loses 4.3 dB and more than half the transmitter power never reaches the antenna. At VHF it can run about 30 m before reaching 3 dB. For anything longer than a short jumper at UHF, step up to LMR-400.
Is LMR-600 worth the extra cost over LMR-400?
On a 25 m UHF run the difference is 0.8 dB (2.2 dB against 1.4 dB), worth roughly 3 W on a 25 W radio, plus the same gain on receive. For a critical repeater or a fringe coverage link that is often worth paying for. For a typical rooftop base station under about 30 m, LMR-400 is usually the sensible choice. Beyond about 35 m at UHF, LMR-600 stops being optional.
Why does UHF need better cable than VHF?
Coax loss rises with frequency, roughly with its square root. Moving from 150 MHz to 450 MHz multiplies the loss on the same cable by about 1.7, so a feedline that is fine on a VHF system can be marginal on UHF.
Should I buy a higher-power radio instead of better cable?
Usually not. Doubling transmit power is worth 3 dB, the same as removing 3 dB of cable loss, but it helps only the outbound path. Range is normally limited by the handheld’s weaker transmitter, and only lower feedline loss improves the base station’s receive side. Fix the cable first.
My VSWR reading looks good. Does that mean the cable is fine?
Not necessarily. Cable loss attenuates reflected power as well as forward power, so a long or lossy cable can make a poor antenna look well matched when you measure at the radio end. To judge the antenna, measure at the antenna end. To judge the cable, compare its measured loss against the datasheet figure.
LMR Coaxial Cable and Connectors for Two-Way Radio Sites
Bravosatcom supplies Times Microwave LMR-400 and LMR-600 cable with matching N-type connectors, plus two-way radios from Motorola, ICOM and Kenwood for base station and repeater installations.