Calculator Inputs
Example Data Table
| Cable | Frequency | Length | Input Power | VSWR | Use Case |
|---|---|---|---|---|---|
| RG-58/U | 144 MHz | 50 ft | 50 W | 1.5 | Short VHF test run |
| LMR-400 | 440 MHz | 75 ft | 25 W | 1.3 | UHF base antenna |
| LMR-600 | 1296 MHz | 100 ft | 10 W | 1.2 | High frequency feed line |
Formula Used
The calculator estimates attenuation by scaling the cable loss rating with frequency. It then adds cable loss, connector loss, inline loss, and mismatch loss.
| Cable loss rate | Loss per 100 ft = reference loss × (frequency / reference frequency)^exponent |
|---|---|
| Cable loss | Cable loss dB = loss per 100 ft × length in feet / 100 |
| Connector loss | Connector loss dB = connector count × loss per connector |
| Reflection coefficient | Γ = (VSWR - 1) / (VSWR + 1) |
| Mismatch loss | Mismatch loss dB = -10 × log10(1 - Γ²) |
| Total loss | Total loss dB = cable loss + connector loss + inline loss + mismatch loss |
| Output power | Output dBm = input dBm - total loss dB |
| Voltage ratio | Voltage ratio = 10^(-total loss dB / 20) |
How To Use This Calculator
- Enter the operating frequency and choose the correct unit.
- Select a cable type or choose custom cable values.
- Enter the total feed line length.
- Add transmitter power, connector count, and connector loss.
- Enter any extra inline device loss, such as filters or switches.
- Add VSWR to estimate mismatch effects.
- Enter antenna gain when you want estimated EIRP.
- Press calculate, then download the result as CSV or PDF.
RF Cable Loss Guide
Why RF Cable Loss Matters
Every radio link loses energy between the transmitter and the antenna. Cable loss is one of the easiest losses to overlook. It grows as cable length increases. It also rises as operating frequency increases. A short feed line can work well at low frequency. The same line may waste useful power at higher bands.
Better Planning Before Installation
This calculator helps you test cable choices before buying parts. You can compare common coax types, connector losses, added device losses, and mismatch effects. You can also enter a custom cable value when a data sheet gives a specific attenuation rating. The result shows total loss, output power, voltage ratio, and remaining power percentage.
Understanding Practical Results
A small loss in decibels can still matter. Three decibels means about half the power is lost. Six decibels leaves about one quarter. Receive systems suffer too, because weak signals lose strength before reaching the receiver. Lower loss cable often improves both transmit and receive performance.
Frequency And Length Effects
Coax attenuation is not fixed for all bands. It usually increases with the square root of frequency, although real cables vary. That is why the calculator scales stored cable values with an exponent. This gives a practical planning estimate. For final work, always compare the answer with the manufacturer data sheet.
Connectors, Adapters, And Mismatch
Connectors and adapters add small losses. One adapter may not matter. Several adapters can reduce the link budget. VSWR also affects delivered power. A poor match reflects some energy back toward the source. The tool reports mismatch loss, return loss, and reflected power percentage.
Choosing A Better Feed Line
Use the output to choose cable size and route length. Shorter runs usually perform better. Better cable helps most at high frequency. Good connectors also help. Keep bends gentle, seal outdoor joints, and avoid unnecessary adapters. A clean feed system protects performance and improves planning confidence. The best choice depends on budget, band, weather exposure, and power level. For portable stations, weight may matter. For fixed sites, lower loss may justify higher cost. Always leave service loops short, neat, and clearly labeled before final field testing.
FAQs
What is RF cable loss?
RF cable loss is the power lost while a signal travels through coaxial cable. It is usually shown in decibels. Higher frequency, longer cable, smaller cable, and poor connectors can increase the loss.
Why does frequency affect cable loss?
Most coaxial cables lose more signal as frequency rises. Skin effect and dielectric losses become stronger at higher frequencies. This is why a cable that works well on HF may perform poorly on UHF or microwave bands.
What does dB loss mean?
dB loss is a logarithmic way to show signal reduction. A 3 dB loss means about half the power remains. A 10 dB loss means only one tenth of the power remains after the loss.
How accurate are the cable values?
The built-in values are planning estimates. Real values vary by brand, construction, temperature, age, and installation quality. For final engineering, compare the result with the exact manufacturer data sheet.
What is mismatch loss?
Mismatch loss happens when the antenna or load impedance does not match the feed line. Some power reflects back toward the transmitter. The calculator uses VSWR to estimate this additional delivered power loss.
Should connector loss be included?
Yes. Each connector, adapter, switch, or jumper can add loss. A single connector may be minor. Many parts together can change the final link budget, especially at higher frequencies.
What is EIRP?
EIRP means effective isotropic radiated power. It combines output power after feed line loss with antenna gain. It helps estimate the radiated strength of the complete transmitter and antenna system.
How can I reduce RF cable loss?
Use a shorter cable run, choose lower loss coax, reduce adapters, install quality connectors, and keep weatherproofing strong. For high frequency systems, upgrading the feed line often gives a clear performance improvement.