Wireless Link Budget

Calculate EIRP, free space path loss, received signal power, and link margin for point-to-point and point-to-multipoint wireless links. Plan MikroTik, Ubiquiti, and other radio deployments with realistic RF link budgets.
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Link Budget Results
Effective Isotropic Radiated Power (EIRP)42.0 dBm
Free Space Path Loss (FSPL)121.7 dB
Received Signal Power-57.7 dBm
Link Margin (fade margin)17.3 dB
Excellent Link Margin

FSPL for 5800 MHz over km is 121.7 dB under free space conditions.

Keep at least 5-10 dB of link margin to tolerate rain, foliage, and multipath fading. For long links, consider rain fade losses on higher frequencies such as 5 GHz and above.

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Overview

The Wireless Link Budget Calculator estimates the effective isotropic radiated power (EIRP), free space path loss (FSPL), received signal power, and link margin for point-to-point and point-to-multipoint radio links. It helps WISPs, network engineers, and installers plan MikroTik, Ubiquiti, Cambium, and other wireless deployments with realistic RF budgets.

Common Use Cases

How to Use

1
Enter the radio transmit power in dBm.
2
Enter the transmitter cable and connector loss in dB.
3
Enter the transmitter antenna gain in dBi.
4
Set the operating frequency in MHz, such as 5800 for 5 GHz or 2400 for 2.4 GHz.
5
Enter the straight-line link distance in kilometers.
6
Enter the receiver antenna gain and cable loss.
7
Set the receiver sensitivity in dBm, matching the modulation level of the link.
8
Optionally add rain or atmospheric loss in dB.
9
Review EIRP, free space path loss, received power, and link margin.

Example Scenario

5 GHz Backhaul Over 5 km

A 5 GHz radio transmits at 20 dBm through 1 dB of cable into a 23 dBi dish. The receive side uses another 23 dBi dish with 1 dB cable loss. Over 5 km the free space path loss is about 121.7 dB, giving a link margin of roughly 35 dB against a -75 dBm receiver sensitivity.

Technical Notes

EIRP is the transmit power after adding antenna gain and subtracting cable losses. Regulatory limits often apply to EIRP for outdoor wireless links.

Free space path loss is the attenuation between two isotropic antennas in free space. FSPL = 20 log10(distance) + 20 log10(frequency) + 32.45, with distance in kilometers and frequency in MHz.

Received power equals EIRP minus path loss plus receive antenna gain minus receive cable loss.

Link margin is the received power above the receiver sensitivity after subtracting rain and atmospheric losses. A margin above 10 dB is generally considered excellent, 5-10 dB is adequate, and below 5 dB is risky.

The free space path loss formula assumes a clear first Fresnel zone. Obstructions, foliage, and reflections add losses beyond free space predictions.

EIRP is typically subject to national regulatory limits. Verify the maximum permitted EIRP for the frequency band before deployment.

Common Mistakes

Frequently Asked Questions

A link margin of at least 10 dB is considered excellent, while 5-10 dB is workable and below 5 dB leaves the link vulnerable to rain, foliage, and fading.

FSPL is calculated as 20 log10(distance in km) plus 20 log10(frequency in MHz) plus 32.45 dB. Longer distance and higher frequency both increase path loss.

EIRP is the effective transmitted power including antenna gain. It matters because regulators cap EIRP for outdoor wireless, and because it is the first term in the received power calculation.

Yes. Path loss assumes a clear line of sight with an unobstructed first Fresnel zone. Buildings, hills, and trees inside the zone add significant loss.

Atmospheric absorption and rain attenuation increase sharply with frequency. Links above 5 GHz need extra fade margin to stay reliable during heavy rain.

Related Topics

RF link budgetFree space path lossEIRPFade marginFresnel zonePoint-to-point radioWISP backhaulAntenna gainReceiver sensitivityMikroTik wireless