Coax Cable Signal Loss Calculator
Calculate signal attenuation in coaxial cable based on cable type, length, and operating frequency for ham radio.
Why coax loss matters:
Every foot of coaxial cable between your radio and antenna absorbs some of your transmitted signal and weakens the received signal by the same amount. At HF frequencies (3–30 MHz), losses are modest. At VHF/UHF (144–440+ MHz), losses can be severe — sometimes consuming more power than reaches the antenna.
Loss is measured in dB (decibels):
| dB Loss | Power Reaching Antenna | Signal Strength Effect |
|---|---|---|
| 1 dB | 79% | Barely noticeable |
| 3 dB | 50% | Half your power is gone |
| 6 dB | 25% | Three-quarters lost |
| 10 dB | 10% | Only 10% reaches antenna |
Common coax cable loss (dB per 100 feet):
| Cable Type | Impedance | 10 MHz | 50 MHz | 144 MHz | 440 MHz | 1296 MHz |
|---|---|---|---|---|---|---|
| RG-58 | 50Ω | 1.1 | 2.5 | 4.5 | 8.0 | 14.5 |
| RG-8X | 50Ω | 0.9 | 2.0 | 3.6 | 6.6 | 12.0 |
| RG-213 | 50Ω | 0.6 | 1.3 | 2.3 | 4.1 | 7.5 |
| LMR-240 | 50Ω | 0.5 | 1.2 | 2.0 | 3.5 | 6.3 |
| LMR-400 | 50Ω | 0.3 | 0.7 | 1.2 | 2.0 | 3.7 |
| LMR-600 | 50Ω | 0.2 | 0.5 | 0.8 | 1.4 | 2.5 |
| Hardline (7/8") | 50Ω | 0.1 | 0.2 | 0.4 | 0.7 | 1.3 |
Loss formula:
Total loss (dB) = (Cable length / 100) × Loss per 100 ft at frequency
Power at antenna (W) = Transmit power (W) × 10^(-loss_dB / 10)
Worked example:
Running 75 feet of RG-213 at 144 MHz with 100 watts:
- Loss rate: 2.3 dB per 100 feet
- Total loss: (75/100) × 2.3 = 1.725 dB
- Power at antenna: 100 × 10^(-1.725/10) = 100 × 0.672 = 67.2 watts
- Power lost as heat: 100 - 67.2 = 32.8 watts wasted
Upgrading to LMR-400 at same length:
- Loss: (75/100) × 1.2 = 0.9 dB
- Power at antenna: 100 × 10^(-0.9/10) = 81.3 watts
- Saves 14 watts just by changing cable type
Connector losses:
Each connector pair (PL-259/SO-239) adds approximately:
- HF (below 30 MHz): 0.1 dB per connector
- VHF (144 MHz): 0.2 dB per connector
- UHF (440 MHz): 0.5 dB per connector
- N-type connectors: about half the loss of PL-259 at UHF and above
Practical advice:
- For HF (below 30 MHz): RG-213 or even RG-8X is fine for most runs under 100 feet
- For VHF/UHF (144/440 MHz): Use LMR-400 for runs over 25 feet
- For microwave (1296+ MHz): Use LMR-600 or hardline
- Keep cable runs as short as practical — put the radio near the antenna if possible