Coax Loss Calculator
Calculate coaxial cable attenuation, total feedline loss, power delivered, and efficiency from cable type, frequency, and run length.
Calculator is for informational purposes only. Terms and Conditions
Preset cable attenuation is based on verified manufacturer equations or published attenuation tables and assumes a matched line under the stated source conditions.
Enter the coax run
Choose the actual cable family, then enter the operating frequency and one-way physical cable length.
Power is optional for attenuation-only work. Use Custom Published Loss when you have an exact datasheet attenuation value for a cable not listed.
Result
Total feedline loss is shown first, followed by cable attenuation, efficiency, and power delivery checks.
Result details
- Cable attenuation—
Show calculation steps Review the cable model, conversions, attenuation scaling, and power transfer
- Enter valid values to see the complete calculation.
Power Through the Feedline
The bar view shows the percentage of input power delivered to the load versus not delivered because of the entered passive path loss.
- Enter valid values to populate the chart.
Method, Sources, and Assumptions
The active cable preset determines whether the calculator uses a manufacturer attenuation equation, calculator interpolation between published table points, or your own datasheet value.
Preset data is taken from manufacturer technical literature. Published attenuation is scaled linearly with physical cable length in decibels.
- Matched-line attenuation only; real installations can add loss from connectors, adapters, moisture, aging, bends, and mismatch.
Calculator guide
How to Read a Coax Loss Result
The coax loss calculator above estimates matched-line attenuation for a selected coax cable at the operating frequency and one-way cable length you enter. Its primary result is total feedline loss in decibels. If you also enter source power, the calculator converts that loss into the power expected at the load; Advanced Options can add known passive component loss without hiding it inside the cable value.
Coax loss is not a fixed number for a cable name. It depends on frequency and physical run length, and manufacturer data for the exact cable construction is the best basis when accuracy matters. The calculator therefore uses manufacturer equations or published attenuation tables for its presets and keeps mismatch effects outside the matched-line loss model.
- Minimum inputs
- Cable type, operating frequency, and one-way cable length
- Primary output
- Total feedline loss in dB
- Key scope
- Matched-line cable attenuation plus any passive loss you explicitly add
How to Use the Coax Loss Calculator
Use the shortest path that matches the information you actually know: select a listed cable when the exact preset applies, or choose Custom Published Loss when you have a datasheet attenuation value for another coax.
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Choose the coax cable
Select the manufacturer-backed preset that matches the installed cable. The listed choices include Times Microwave LMR-195, LMR-240, LMR-400, and LMR-600 plus selected Belden RG-58/U-class, RG-213, and RG-6 products. Do not substitute a similar-looking family name when the exact construction or part number is different.
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Enter operating frequency and one-way cable length
Frequency may be entered in Hz, kHz, MHz, or GHz, while cable length may be entered in feet or meters. Use the actual routed cable length, including service loops and jumpers that are part of the run, rather than the straight-line distance between equipment.
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Add input power only when you want delivered power
Input power is optional. The calculator accepts mW, W, kW, dBm, and dBW. Leaving power blank still gives the dB loss and percentage delivered because those values depend on attenuation, not on the absolute starting power.
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Use Advanced Options for known passive loss and impedance checking
Enter the combined insertion loss of connectors, adapters, lightning protectors, filters, switches, or other passive components only when you have a defensible value. The System Impedance control is advisory: it warns about a nominal cable/system mismatch but does not add guessed mismatch loss.
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Use Custom Published Loss at the same frequency as the datasheet value
In custom mode, enter the manufacturer attenuation in dB/100 ft, dB/100 m, dB/ft, or dB/m at the operating frequency. The calculator scales that published attenuation by physical cable length; it does not create a new frequency curve from a single data point.
Coax Loss Formula and Calculation Method
The calculator first determines attenuation at the selected frequency, scales that attenuation to the entered run length, adds any known passive loss, and then converts total dB loss into a power ratio.
Scale published attenuation to cable length
Plain language: cable loss equals the attenuation rate at the operating frequency multiplied by the cable length expressed in hundreds of feet. The same relationship applies when the attenuation rate is stated per 100 meters or another supported length basis.
Add passive path losses separately
Plain language: known connector or accessory insertion losses are added in dB. Keeping them separate makes it clear how much loss belongs to the coax itself.
Convert dB loss to power delivered
Plain language: every positive loss in dB reduces the remaining power by a logarithmic ratio. A 3 dB loss leaves about one-half of the starting power, while a 10 dB loss leaves one-tenth.
Manufacturer equation used by the LMR presets
For the Times Microwave LMR presets, frequency is in MHz and the selected coefficient set returns attenuation in dB/100 ft. The calculator uses the coefficients published for the exact LMR family rather than applying one generic frequency multiplier to every coax.
The Belden presets use published attenuation-table points instead and interpolate only inside the verified table range.
- \(L_{\mathrm{cable}}\)
- Coax-only loss Matched-line attenuation caused by the selected coax over the entered physical run.
- \(\alpha(f)\)
- Attenuation at frequency Manufacturer-backed loss rate evaluated or interpolated at the operating frequency.
- \(f\)
- Operating frequency RF or IF frequency passing through the coax.
- \(\ell\)
- Cable length One-way physical length of coax included in the calculation.
- \(L_{\mathrm{add}}\)
- Additional passive loss Known insertion loss from passive components that is not already part of the cable attenuation.
- \(L_{\mathrm{total}}\)
- Total feedline loss Coax-only loss plus the additional passive loss entered in Advanced Options.
- \(\eta\)
- Power-delivery fraction Fraction of input power remaining after the entered total loss.
- \(P_{\mathrm{in}}, P_{\mathrm{out}}\)
- Input and output power Power before the modeled feedline loss and the power remaining at the load after that loss.
Worked Coax Loss Example
Use the same illustrative state loaded by the calculator: 100 ft of Times Microwave LMR-400 at 146 MHz, 100 W input power, and 0 dB of additional passive loss.
Calculate LMR-400 attenuation at 146 MHz
Scale the attenuation to 100 ft
Convert loss to delivered power
Result
Total feedline loss ≈ 1.531 dB
About 70.30% of the input power remains after the modeled loss, so a 100 W source delivers about 70.30 W to the load under the matched-line assumptions. About 29.70 W is not delivered to the load because of the modeled attenuation.
How to Interpret Coax Loss in dB
A dB loss is logarithmic, so the most useful interpretation is often the percentage of power that remains. The table below converts several common loss values using \(10^{-L/10}\).
| Loss | Power remaining | Power not delivered |
|---|---|---|
| 0.5 dB | 89.1% | 10.9% |
| 1 dB | 79.4% | 20.6% |
| 2 dB | 63.1% | 36.9% |
| 3 dB | 50.1% | 49.9% |
| 6 dB | 25.1% | 74.9% |
| 10 dB | 10.0% | 90.0% |
Loss affects transmit and receive paths
For a passive coax run, insertion loss reduces RF power passing through the line in either direction. On transmit that appears as less power reaching the antenna or load; on receive it appears as signal attenuation before the receiver input.
Length is linear in dB
Holding cable type and frequency constant, doubling the physical cable length doubles the coax loss in dB. A 50 ft run therefore has half the dB attenuation of the same cable at 100 ft under the same matched-line conditions.
There is no universal acceptable loss
Whether 1 dB, 2 dB, or 3 dB is acceptable depends on the complete RF system: available link margin, antenna gain, transmitter power, receiver sensitivity, noise requirements, installation length, cable cost, and mechanical constraints.
How much coax loss is acceptable?
A useful way to judge the result is to translate dB into remaining power rather than apply an arbitrary good/bad label. At 1 dB, about 79.4% of the input power remains; at 2 dB, about 63.1%; at 3 dB, about 50.1%; and at 6 dB, only about 25.1% remains. The acceptable value is the loss your complete RF link can tolerate while still meeting the required performance margin.
Why Coax Loss Increases With Frequency
Coax attenuation generally rises as frequency increases because both conductor-related loss and dielectric loss increase. The exact curve depends on cable construction, which is why manufacturer-specific equations or tables are preferable to one generic frequency multiplier.
Skin effect raises conductor loss
As frequency rises, RF current becomes increasingly concentrated near the conductor surfaces. The effective conducting cross-sectional area becomes smaller and AC resistance rises. The square-root-of-frequency term in common coax attenuation equations reflects much of this conductor-loss behavior.
Dielectric loss also grows with frequency
The insulating material between the inner and outer conductors dissipates some RF energy. Its contribution becomes more important at higher frequency, which is why a simple \(\sqrt{f}\) scaling alone does not accurately describe every cable across a wide frequency range.
Why Real Coax Loss Can Be Higher
The calculator models the selected cable from published matched-line data. An installed feedline can measure differently when connectors, accessories, mismatch, damage, environment, or aging add effects that are not part of the nominal cable attenuation.
Connectors and passive accessories
Adapters, lightning protectors, filters, RF switches, and connectors can add insertion loss. Enter a known combined value in Additional Passive Loss when you have manufacturer or measured data, and avoid counting a loss twice if it is already included in an assembly specification.
Impedance mismatch and SWR
Published attenuation normally describes a matched line. A mismatched load creates a reflected wave, so part of the RF energy travels through the lossy line again. The resulting system loss can therefore exceed the simple matched-line attenuation shown by the cable datasheet.
A lossy line can make transmitter-end SWR look better
The reflected wave is attenuated on its trip back toward the source. As feedline loss increases, an SWR measurement made at the radio can appear less severe than the mismatch that actually exists at the antenna or load. That is one reason a good-looking transmitter-end SWR does not prove the feedline is low loss.
Water ingress, corrosion, and damaged cable
Field damage can make an installed feedline perform worse than new-cable data. If measured insertion loss is materially higher than the calculator result, inspect weather seals, connectors, shield continuity, crushed sections, sharp bends, and any location where moisture could enter.
Temperature and exact product construction
Manufacturer attenuation values are published for stated reference conditions and a specific construction. Cable family names should not be treated as universal electrical specifications across every manufacturer, jacket, dielectric, center-conductor, or flexible variant.
Receive systems can be especially sensitive to feedline loss
Loss ahead of the receiver attenuates weak incoming signals before they reach the first active stage. This is why systems such as ADS-B, satellite reception, GNSS, SDR, and weak-signal VHF/UHF often benefit from minimizing coax loss or placing a low-noise amplifier close to the antenna when the system design supports it.
How to Choose Lower-Loss Coax
Choose coax by comparing loss at the actual operating frequency and installed length, then check the electrical and mechanical requirements that the attenuation number does not capture. There is no single cable that is automatically best for every RF system.
Compare at the exact frequency
A small difference between cables at HF can become much larger at UHF or microwave frequencies. This is why the calculator evaluates attenuation at the entered frequency instead of assigning one loss number to each cable type.
Compare the full installed length
The lower-loss choice becomes more valuable as the run gets longer because dB loss scales with physical length. Include jumpers and other coax sections that are actually in the RF path.
Keep 50 Ω and 75 Ω systems distinct
A 75 Ω cable can have attractive matched-line attenuation and still be a mismatch in a nominal 50 Ω system. The calculator’s impedance warning is a prompt to check the complete transmission-line design, not a statement that one impedance is universally better.
Verify power, connectors, routing, and environment
Attenuation alone does not establish suitability. Before choosing a cable, verify the manufacturer’s frequency range, average and peak power limits when relevant, compatible connector system, minimum bend radius, jacket/environmental rating, and installation constraints.
Coax Loss Reference Values
Reference data is most useful when it stays tied to a specific manufacturer and product. The values below illustrate why generic RG-family labels should not be treated as exact attenuation specifications.
| Frequency | Nominal attenuation |
|---|---|
| 862 MHz | 22.1 dB/100 m |
| 1000 MHz | 24.1 dB/100 m |
| 1350 MHz | 29.0 dB/100 m |
| 1750 MHz | 34.3 dB/100 m |
| 2150 MHz | 39.1 dB/100 m |
| 2400 MHz | 42.4 dB/100 m |
Source: Belden MRG2132 technical data. Belden identifies these as nominal attenuation values and notes that maximum attenuation may be higher. Use the current datasheet for the exact product being installed.
Assumptions and Limits
This is a matched-line attenuation calculator and preliminary RF planning tool. It is deliberately transparent about what is calculated and what still requires system-specific data.
Manufacturer data is the baseline
Preset attenuation is based on manufacturer equations or published table values for specific cable families or products. These are nominal or typical data under the source’s stated conditions, not a measurement of your installed cable.
Table presets do not extrapolate
For published-table cables, the calculator interpolates only between verified frequency points and blocks frequencies outside the supported table range instead of inventing an extrapolated value.
Mismatch is not solved from nominal impedance
The System Impedance option provides a warning when the selected cable’s nominal impedance differs from the selected system impedance. It does not calculate reflection coefficient, SWR, return loss, or additional mismatch-related feedline loss.
Power rating is not verified
Entering transmitter power lets the calculator report power remaining after loss; it does not confirm that the cable, connectors, or accessories are rated for that power at the selected frequency or environmental condition.
Data Sources and Verification
The calculator and guide use manufacturer data for cable-specific attenuation and independently derived dB-to-power relationships for interpretation. Exact product data takes precedence over generic cable-family assumptions.
- Times Microwave Systems — LMR Complete Guide — supports the LMR attenuation coefficient method, cable-specific coefficient sets, frequency scope, and related product data.
- Times Microwave Systems — Coaxial Cable Attenuation and Power Calculator — provides the manufacturer’s current calculator and a direct external check on LMR attenuation behavior.
- Belden MRG2132 Technical Data — supports the RG-213 preset attenuation table through 2.4 GHz and the stated nominal-table scope.
- Belden 8240 Technical Data — supports the RG-58/U-class representative product data, including its nominal 52 Ω characteristic impedance.
- Belden 1694A Product Data — supports the 75 Ω RG-6-class reference product and its published frequency-dependent attenuation data.
The worked example was checked two ways: first from the published LMR-400 attenuation equation, then by reversing the resulting power ratio back to dB. The two calculations agree before display rounding.
Coax Loss Calculator FAQs
These questions address common decisions that come up after calculating feedline attenuation.
How much coax loss is there per 100 feet?
There is no single loss value per 100 ft because attenuation depends on the exact cable and operating frequency. Use the manufacturer’s attenuation value or equation for the specific product at the frequency of interest, then scale it to the actual run length.
Does coax loss affect reception as well as transmission?
Yes. Passive coax attenuation reduces RF signals traveling through the line in either direction. On receive, feedline loss occurs before the receiver input, so minimizing loss is especially important when working with weak signals.
Can I use RG-6 in a 50-ohm RF system?
RG-6 is commonly a nominal 75 Ω cable, while many radio systems are nominally 50 Ω. It may be usable in a deliberately designed system, but lower matched-line attenuation alone does not prove interchangeability. Check the complete impedance transformation, reflections, connectors, and equipment requirements before substituting it.
Why can SWR measured at the radio look better than SWR at the antenna?
A lossy feedline attenuates both the forward and reflected waves. The reflected wave is smaller by the time it returns to a meter at the transmitter, so the measured transmitter-end SWR can appear less severe than the actual mismatch at the load.
How can I measure actual coax cable loss?
For an installed assembly, use a calibrated RF measurement method appropriate to the frequency range, such as a vector network analyzer or other insertion-loss setup, and compare the measured result with the current datasheet value for the exact cable and connectors. The measurement should include the same adapters and accessories that are part of the real RF path.
Should I use the highest frequency for a wideband coax run?
For a conservative attenuation check across a band, evaluate the cable at the highest operating frequency because coax loss generally increases with frequency. If the system has multiple critical channels or the manufacturer data is irregular, check each relevant frequency rather than relying on one point.