Coax Cable Loss Calculator
Select your cable type, enter frequency and length, and see how much signal reaches your antenna. Compare common coax types to find the right cable for your station.
Common thin 50-ohm cable. Short runs only at VHF/UHF.
Understanding Coax Cable Loss
Every foot of coaxial cable between your radio and antenna absorbs some of your signal. This attenuation is caused by two factors: resistive loss in the copper conductors and dielectric loss in the insulating material between them. Both increase with frequency, which is why VHF and UHF stations need to pay more attention to feed line quality than HF operators.
The practical impact is straightforward: 3 dB of loss means half your transmit power is being converted to heat inside the cable instead of being radiated by your antenna. On receive, the same 3 dB loss makes weak signals 3 dB harder to hear. For a VHF/UHF station where every dB matters, choosing the right coax and keeping runs short is one of the easiest performance wins available.
The Loss Formula
Coax attenuation follows a predictable pattern: Loss(f) = A * sqrt(f) + B * f, where A is the conductor loss coefficient (dominant at lower frequencies) and B is the dielectric loss coefficient (becomes significant at UHF and above). Both are specific to each cable type.
Worked example: 50 feet of RG-58 at 446 MHz (GMRS). Loss per 100 ft is about 7.0 dB, so 50 ft gives 3.5 dB of total loss. That means only 45% of your transmit power reaches the antenna, and received signals are 3.5 dB weaker than they would be at the antenna terminals. Switching to LMR-400 drops the loss to about 1.2 dB for the same run, delivering 76% of your power.
Coax Cable Comparison
Loss per 100 feet at common ham radio frequencies:
| Cable | Impedance | 28 MHz | 146 MHz | 440 MHz |
|---|---|---|---|---|
| RG-174 | 50 ohm | 3.3 dB | 7.5 dB | 13.2 dB |
| RG-58 | 50 ohm | 1.7 dB | 4.0 dB | 7.0 dB |
| RG-8X | 50 ohm | 1.4 dB | 3.1 dB | 5.5 dB |
| RG-213 | 50 ohm | 0.9 dB | 2.0 dB | 3.5 dB |
| LMR-240 | 50 ohm | 1.2 dB | 2.7 dB | 4.7 dB |
| LMR-400 | 50 ohm | 0.6 dB | 1.4 dB | 2.4 dB |
| LMR-600 | 50 ohm | 0.4 dB | 0.9 dB | 1.6 dB |
Choosing the Right Coax
The best cable for your station depends on three things: operating frequency, cable run length, and how much you are willing to spend. For HF stations with runs under 100 feet, RG-213 is more than adequate. For VHF/UHF base stations with longer runs to a roof or tower-mounted antenna, LMR-400 is the standard choice. LMR-600 is reserved for commercial installations or very long runs where every fraction of a dB counts.
Avoid using RG-58 for any permanent VHF/UHF installation. It is fine for short jumpers (under 10 feet) or HF portable operations, but the loss at 440 MHz makes it unsuitable for runs of any real length. RG-174 should only be used for internal pigtails and test leads.
Looking to optimize your portable station? See our best radios for POTA activations where feed line weight and loss both matter.
Practical Tips for Reducing Feed Line Loss
Keep runs short. Mount your antenna as high as possible, but route the coax efficiently. Every extra foot of cable adds loss. Coiling excess cable at the base of the antenna does not help and can create additional problems.
Use quality connectors. A corroded or poorly installed PL-259 connector can add more loss than 20 feet of good coax. Use weatherproof connectors outdoors and seal all connections with self-amalgamating tape or heat-shrink tubing.
Inspect cable regularly. Water intrusion is the silent killer of coax performance. If your SWR has gradually increased over time, suspect water in the cable. Use the SWR Calculator to check your antenna system.
Frequently Asked Questions
What is coax cable loss?
Coax cable loss (attenuation) is the reduction in signal strength as RF energy travels through a coaxial cable. It is measured in decibels (dB). Loss increases with frequency and cable length, and varies by cable type. Every 3 dB of loss cuts your effective power in half.
Which coax cable has the lowest loss?
Among common ham radio cables, LMR-600 has the lowest loss, followed by LMR-400. However, these thicker cables are harder to route and more expensive. For most VHF/UHF base station setups, LMR-400 is the best balance of low loss, flexibility, and cost. For short jumpers, RG-8X or RG-213 are fine.
How much coax loss is acceptable?
Under 1 dB of total feed line loss is excellent. Up to 3 dB is acceptable for most ham stations, though you are losing up to half your power. Above 3 dB, consider shortening your cable run or switching to a lower-loss cable type. At 6 dB, 75% of your power is wasted as heat in the cable.
Does coax loss affect receive as well as transmit?
Yes. Coax loss works both ways. The same attenuation that reduces your transmitted signal also reduces incoming signals before they reach your receiver. On VHF/UHF, where received signals are often weak, high feed line loss can be the difference between hearing a station and missing it entirely.
Does coax cable loss change with temperature?
Yes, but the effect is small for most ham radio applications. Cable loss increases slightly in hot weather because conductor resistance rises with temperature. The change is typically under 10% across normal outdoor temperature ranges. Frequency and cable type have a much larger impact than temperature.