Cable Loss Calculator
Estimate RF coax attenuation based on cable type, frequency, run length, and connector losses.
Model uses attenuation scaling with √frequency (relative to 100 MHz), which is a practical approximation for many coaxial cables.
What Is Cable Loss?
Cable loss (also called attenuation) is the amount of signal power that disappears as a signal travels down a cable. In RF systems, this is usually measured in decibels (dB). The longer the cable and the higher the frequency, the greater the loss tends to be.
Even small losses matter. A few dB can significantly reduce received signal quality, lower link margin, or waste transmitter power before it reaches the antenna or device.
How This Calculator Works
This cable loss calculator starts with an attenuation rating in dB per 100 feet at 100 MHz. It then adjusts that value for:
- Actual cable length (longer run = more loss)
- Operating frequency (higher frequency = more loss)
- Connector and splice losses (small per item, but cumulative)
- Optional fixed losses (filters, adapters, feedthroughs, etc.)
Core Formula
Total loss is estimated as:
Total Loss (dB) = Cable Loss + Connector Loss + Extra Loss
Where:
- Cable Loss = Base attenuation × (Length/100 ft) × √(Frequency/100 MHz)
- Connector Loss = Connector count × Loss per connector
Why Frequency Matters So Much
At lower frequencies, the signal penetrates conductor surfaces more deeply, and effective resistance is lower. As frequency rises, skin effect and dielectric behavior increase attenuation. That is why a cable that performs fine at 50 MHz may be very lossy at 2.4 GHz.
Quick Practical Example
Suppose you use 150 ft of RG-58 at 900 MHz with 2 connectors at 0.1 dB each:
- Base attenuation: 1.5 dB/100 ft @ 100 MHz
- Frequency multiplier: √(900/100) = 3
- Cable loss: 1.5 × 1.5 × 3 = 6.75 dB
- Connector loss: 2 × 0.1 = 0.2 dB
- Total loss: 6.95 dB
That means only about 20% of input power reaches the far end. Choosing lower-loss cable can dramatically improve performance.
How to Reduce Cable Loss
1) Shorten the run
Every extra meter adds attenuation. Keep cable runs as short as your installation allows.
2) Use better cable
Upgrading from RG-58 to a lower-loss cable like LMR-400 can save several dB, especially at UHF and microwave frequencies.
3) Minimize connectors and adapters
Each interface adds insertion loss and potential mismatch. Use high-quality connectors and avoid unnecessary transitions.
4) Match cable to frequency range
Not all cable families are efficient at high frequency. Check manufacturer attenuation charts for your exact frequency.
Interpreting dB in Real Terms
- 3 dB loss ≈ about 50% power delivered
- 6 dB loss ≈ about 25% power delivered
- 10 dB loss ≈ about 10% power delivered
Because dB is logarithmic, “just a few dB” can represent a major system change.
Important Notes
- This is an engineering estimate, not a substitute for manufacturer sweep data.
- Real loss varies with temperature, bend radius, moisture, connector quality, and VSWR.
- For precision design, always validate with cable datasheets and field measurements.
Final Takeaway
A cable loss calculator helps you make better decisions before you buy or install hardware. By checking attenuation early, you can avoid weak links, preserve signal quality, and design a more reliable RF system.