Coax Cable Loss Calculator

Coaxial cable — the shielded signal wire used in antennas, TV, and radio systems — loses power over distance, and that loss gets worse at higher frequencies and with antenna mismatch. The Coax Cable Loss Calculator takes your frequency, cable length, cable loss per 100ft, SWR, and input power to calculate Total Cable Loss in dB. Secondary outputs include matched load loss, additional SWR loss, power at the load, power lost, and transmission efficiency.

MHz

Operating frequency in MHz

Length of coaxial cable

Length Units *

dB

Manufacturer specified loss in dB per 100 feet at the operating frequency

Standing wave ratio at the load

watts

Transmitter output power in watts

Results

Total Cable Loss

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Matched Load Loss

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Additional SWR Loss

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Power at Load

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Power Lost

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Transmission Efficiency

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Frequently Asked Questions

What is coaxial cable loss and why does it matter?

Coaxial cable loss, or attenuation, is the reduction in signal strength as it travels through the cable. This loss is measured in decibels (dB) and increases with frequency and cable length. Higher loss means less power reaches your antenna, reducing transmission range and reception sensitivity.

How does SWR affect cable loss?

Standing Wave Ratio (SWR) increases cable loss beyond the normal matched-load loss. When SWR is greater than 1:1, reflected power travels back down the cable, causing additional attenuation. Higher SWR values result in significantly more loss, especially in lossy cables.

What cable loss specification should I use?

Use the manufacturer's loss specification for your cable type at your operating frequency. Common values are 2-3 dB per 100ft for RG-8, 4-5 dB per 100ft for RG-58, and 0.4-0.7 dB per 100ft for low-loss cables like LMR-400. Always check the datasheet for your specific frequency.

How can I minimize coaxial cable loss?

Use the shortest cable run possible, choose low-loss cable types (like LMR-400 instead of RG-58), maintain good SWR (keep it below 2:1), and ensure proper connector installation. For long runs or high frequencies, consider hardline or waveguide alternatives.

Is cable loss the same for transmit and receive?

Yes, cable loss is reciprocal - the same loss occurs whether transmitting or receiving. A 3 dB loss on transmit means 3 dB less signal reaches the antenna, and on receive, it means 3 dB less sensitivity to incoming signals.

How does frequency affect coaxial cable loss?

Cable loss increases with frequency due to skin effect and dielectric losses. Loss typically increases roughly proportional to the square root of frequency. For example, loss at 450 MHz will be about 1.7 times higher than at 146 MHz for the same cable.

What is the difference between matched load loss and total loss?

Matched load loss is the basic cable attenuation when terminated in its characteristic impedance (usually 50 ohms). Total loss includes additional loss due to SWR mismatch. At SWR 1:1, matched and total loss are equal.

How accurate are these cable loss calculations?

These calculations are quite accurate for typical installations when using correct manufacturer specifications. However, factors like connector quality, cable aging, moisture ingress, and temperature can affect actual performance. Regular measurements with an SWR analyzer are recommended.