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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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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.
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.
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.
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.
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.
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.
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.
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.