How do I calculate coax cable loss?

Cable loss = (attenuation spec in dB/100ft) × (run length in ft / 100). For example, LMR-400 at 144 MHz has a spec of 1.5 dB/100ft. A 50-foot run loses 0.75 dB. This calculator does the interpolation automatically for any frequency and length.

What is a good dB loss for a coax cable run?

For receive systems (SDR, ADS-B, scanner), keep total cable loss under 3 dB if possible. For transmit, under 1.5 dB is ideal. Every 3 dB of loss halves the power. On receive paths, every dB of cable loss raises the effective noise figure by 1 dB.

How much loss is acceptable in coax?

For HF transmit (below 30 MHz), up to 3 dB is acceptable for most stations. For VHF/UHF transmit, aim for under 2 dB. For sensitive receive systems like ADS-B or weak-signal work, under 1 dB is preferable. Use a low-noise amplifier (LNA) at the antenna to compensate for longer cable runs.

Does longer coax reduce signal?

Yes — signal loss increases linearly with cable length and increases with frequency. Doubling the cable length doubles the loss in dB. This is why LMR-400 or LMR-600 is recommended for long runs rather than RG-58, which has significantly higher loss per foot.

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Coax Cable Loss Calculator

Enter your cable type, run length, transmit power, and operating frequency to calculate signal loss and watts at the antenna.

Cable Type

Run Length (feet)

Frequency (MHz)

Transmit Power (watts) optional

Select a cable and enter your parameters above to see results.

Compare All Cables at Your Settings

Loss for each cable at the frequency and length you entered above.

Cable	Loss (dB)	Watts at Antenna	% Retained
Enter frequency and length above to compare cables.

Frequently Asked Questions

How do I use this calculator?

Select your cable type from the dropdown, enter your run length in feet, set the operating frequency in MHz (or use a preset button), and optionally enter your transmit power. Results appear instantly.

What does dB cable loss mean in practice?

Every 3 dB of cable loss halves your power. At 6 dB loss, you're delivering 25% of your transmit power to the antenna. On receive, every dB of cable loss directly raises the noise figure — making weak signals harder to detect.

Which cable should I choose for my run?

For runs under 15 feet at VHF/UHF: LMR-195 or RFC-195. For 15–50 feet: LMR-240 or RFC-240. For 50 feet and beyond: LMR-400 or RFC-400. For runs over 150 feet: LMR-600.

Does this calculator account for connector losses?

No — connector losses are not included. Each high-quality connector adds approximately 0.05–0.1 dB. For a 2-connector assembly (one at each end), add 0.1–0.2 dB to the calculated cable loss for a more accurate total.

How Coaxial Cable Signal Loss Works

Coaxial cable attenuation is caused by two mechanisms: conductor loss (resistive loss in the center conductor and shield) and dielectric loss (energy absorbed by the insulating material between conductors). Both increase with frequency — which is why a cable that performs well at HF (below 30 MHz) may be completely unsuitable at 2.4 GHz.

Loss scales linearly with cable length. If 25 feet of RG-58 at 144 MHz loses 1.5 dB, then 50 feet will lose 3.0 dB, and 100 feet will lose 6.0 dB. This is why upgrading to a lower-loss cable pays off more on long runs — the per-foot savings compound over the entire run.

A useful rule of thumb: every 3 dB of loss halves your signal power. At 6 dB loss, only 25% of your transmit power reaches the antenna. On receive, every 1 dB of cable loss raises your effective noise figure by 1 dB — which directly degrades sensitivity for weak-signal applications.

Cable Loss Reference: Common Coax Types

The table below shows approximate loss in dB per 100 feet at common frequencies. Lower numbers are better. Use this as a guide when comparing cables for your application.

Cable	30 MHz (HF)	144 MHz (VHF)	440 MHz (UHF)	2.4 GHz (WiFi)
RG-58	0.55 dB	1.3 dB	2.5 dB	7.0 dB
RG-8X	0.4 dB	0.9 dB	1.8 dB	5.5 dB
LMR-195 / RFC-195	0.4 dB	0.8 dB	1.5 dB	4.5 dB
LMR-240 / RFC-240	0.25 dB	0.6 dB	1.1 dB	3.2 dB
RG-213 / RG-8	0.25 dB	0.6 dB	1.1 dB	3.5 dB
LMR-400 / RFC-400	0.13 dB	0.3 dB	0.55 dB	1.5 dB
LMR-600	0.09 dB	0.2 dB	0.37 dB	1.0 dB

Values are approximate dB/100ft. Actual loss varies by manufacturer and cable condition.

Which Cable Should You Use?

Short runs under 15 ft

Loss is minimal at any cable grade. RG-58, LMR-195, or RG-316 all work fine. Use RG-316 or LMR-195 for tight bends or space-constrained installs. Connector quality matters more than cable at this length.

15–50 ft at VHF/UHF

LMR-240 or RFC-240 is the sweet spot — meaningfully lower loss than RG-58 without the bulk of LMR-400. RG-213 is a good budget option for lower frequencies (HF through 2m).

50–150 ft or 2.4 GHz WiFi/cellular

LMR-400 or RFC-400 is the standard recommendation. At 2.4 GHz, RG-58 would lose over 70% of power in a 100-foot run. LMR-400 keeps that under 30%. For outdoor or semi-permanent runs, use a UV-resistant jacket variant.

Long runs 150 ft+

LMR-600 at 0.55 dB/100ft (at 450 MHz) is the practical choice for most amateur and commercial installations. For runs over 300 feet, consider Heliax or LMR-900 to keep total loss under 3 dB.

Transmit vs. Receive: Why the Threshold Differs

For transmit applications, cable loss directly wastes power — but your amplifier compensates to some degree. Up to 3 dB of loss is generally acceptable for most licensed transmit installations. Beyond 6 dB, you're delivering less than 25% of your rated power to the antenna.

For receive-only applications (SDR, ADS-B, scanners, GPS, weather satellite), cable loss is far more critical. Every 1 dB of cable loss directly raises the noise figure of your system by 1 dB. A 3 dB cable run doubles the effective noise floor, making weak signals disappear. Keep receive path loss under 1.5 dB — or place a low-noise amplifier (LNA) directly at the antenna to mitigate it.

For duplex or transceiver setups (like ham radio base stations), the receive path is usually the limiting factor. Design your feedline around the receive loss budget, and the transmit path will generally be well within acceptable limits.

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