Example Data Table
| Cable |
Length |
Frequency |
Input Power |
Typical Use |
| RG-58 |
50 ft |
146 MHz |
25 W |
Short VHF jumper |
| LMR-400 |
100 ft |
450 MHz |
50 W |
Base station feeder |
| LMR-600 |
150 ft |
915 MHz |
10 W |
Long low loss run |
| Half Inch Hardline |
200 ft |
1296 MHz |
20 W |
Microwave installation |
Formula Used
Frequency adjusted cable loss: cable loss = reference loss × square root of frequency divided by reference frequency × length in feet divided by 100.
Temperature adjusted loss: adjusted loss = cable loss × [1 + temperature difference × coefficient / 100].
Connector loss: connector loss = connector count × loss per connector.
Reflection coefficient: gamma = (VSWR - 1) / (VSWR + 1).
Mismatch loss: mismatch loss = -10 × log10(1 - gamma squared).
Total loss: total loss = cable loss + connector loss + mismatch loss + extra inline loss.
Output power: output dBm = input dBm - total loss.
Watts conversion: watts = 10 raised to ((dBm - 30) / 10).
Link margin: margin = output dBm + downstream gain - receiver sensitivity.
How to Use This Calculator
- Select a cable type or choose custom for your own data sheet value.
- Enter the cable length and select feet or meters.
- Add the operating frequency in MHz.
- Enter transmitter or source power in watts or dBm.
- Add connector count, connector loss, and any extra inline loss.
- Enter VSWR when mismatch needs to be included.
- Use temperature fields when outdoor cable heating matters.
- Press the calculate button and review the result above the form.
- Use CSV or PDF buttons to save the calculated report.
RF Cable Attenuation Planning Guide
Understanding RF Cable Attenuation
RF cable attenuation is the signal loss that happens as energy travels through coaxial cable. The loss is measured in decibels. It grows as cable length increases. It also rises when frequency increases. A short jumper at low frequency may lose little power. A long feeder at microwave frequency can remove a large share of transmitter power before it reaches the antenna.
Why Reference Data Matters
Good planning starts with the cable data sheet. Most sheets list attenuation per 100 feet or per 100 meters at standard frequencies. This calculator uses that reference loss and scales it with the square root of frequency. That method is a practical estimate for many coax types. It is not a replacement for certified lab data, but it gives a useful engineering check.
Connectors and Small Losses
Connector loss is often ignored. That can create optimistic results. Each connector, adapter, arrester, and jumper adds insertion loss. Small losses matter when a receiver needs a weak signal. The tool lets you enter connector count and loss per connector. It also includes optional extra loss for splitters, filters, bends, aging, or installation quality.
Power and Link Budget
Power can be entered in watts or dBm. The calculator converts both formats into one link budget. It subtracts total cable loss from input power. Then it reports output power, remaining percentage, and voltage across the selected impedance. This helps compare radio output with antenna input. It also helps confirm whether a receiver still has enough margin.
Mismatch and VSWR
Mismatch is another useful detail. A high VSWR means some power is reflected. The reflected portion acts like extra loss. The tool estimates mismatch loss from VSWR. Keep VSWR values realistic, because severe mismatch can damage transmitters or distort measurements.
Temperature Effects
Temperature can also change attenuation. Coax loss normally increases as cable gets warmer. Outdoor runs may see large seasonal changes. The temperature adjustment in this calculator is simple. It applies a coefficient to the cable loss. Use a cable specific value when possible.
Better Design Decisions
For best results, enter measured values when available. Use conservative assumptions for unknown connectors and accessories. Compare several cable types before buying material. A lower loss cable may cost more, yet it can save amplifier power and improve receive sensitivity. Always verify critical RF systems with proper instruments before final deployment.
FAQs
1. What is RF cable attenuation?
RF cable attenuation is the signal power lost while traveling through coaxial cable. It is normally measured in decibels. Longer cable and higher frequency usually create greater loss.
2. Why does frequency affect cable loss?
At higher frequencies, conductor and dielectric losses increase. This makes the same cable lose more signal at UHF or microwave bands than at lower HF or VHF bands.
3. Can I use custom cable data?
Yes. Select Custom and enter the loss per 100 feet plus the reference frequency. Use values from a data sheet for better estimates.
4. What does connector loss mean?
Connector loss is the insertion loss caused by plugs, adapters, arresters, or couplers. A small value per connector can become important in sensitive RF systems.
5. What is mismatch loss?
Mismatch loss estimates the extra loss caused by reflected power. It is based on VSWR. Higher VSWR means more reflected power and less delivered power.
6. Why include temperature adjustment?
Cable attenuation can rise when cable temperature increases. Outdoor feeders may heat in sunlight, so temperature adjustment gives a more conservative estimate.
7. What is link margin?
Link margin is the difference between available signal and receiver sensitivity after selected gain or loss. Positive margin usually means the signal is above the required level.
8. Is this calculator suitable for final certification?
No. It is useful for planning and comparison. Final RF systems should be tested with calibrated instruments and checked against manufacturer data.