Point-to-Point Link Calculator
Close a point-to-point wireless link: free-space path loss, received signal level, EIRP and the fade margin left over.
About Point-to-Point Link Calculator
Free-space path loss grows 6 dB for every doubling of distance and 6 dB for every doubling of frequency. Adding transmitter power and antenna gain, then subtracting every loss along the path, gives the level arriving at the receiver; the difference from its sensitivity is the fade margin. A link that closes with 3 dB of margin works on the day you commission it and drops during the first heavy rain, so margin — not raw signal level — is the number that decides whether the hop is production-ready.
Formulas
Point-to-Point Link
FSPL = 20·log10(d_km) + 20·log10(f_MHz) + 32.44; received level = Tx power + antenna gains − cable losses − FSPL − misc losses; fade margin = received level − sensitivity.
- fspl
- Loss from spreading alone, before any obstruction
- fadeMargin
- Decibels of signal you can lose before the link drops
Regulatory EIRP
EIRP = transmit power + antenna gain − cable loss, which is the figure regulators cap.
Worked example
With the default values below, Point-to-Point Link Calculator returns Fade Margin of 26.7. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Link distanceaccepts 0.01–200 km
- 12 km
- Frequencyaccepts 100–90,000 MHz
- 5,800 MHz
- Transmit poweraccepts -10–50 dBm
- 23 dBm
- Transmit antenna gainaccepts 0–60 dBi
- 27 dBi
- Receive antenna gainaccepts 0–60 dBi
- 27 dBi
- Cable and connector loss per endaccepts 0–20 dB
- 1.5 dB
- Rain, foliage and misc lossesaccepts 0–40 dB
- 3 dB
- Receiver sensitivityaccepts -110–-40 dBm
- -85 dBm
Results
- Fade Margin
- 26.7 dB
- Free-Space Path Loss
- 129.29 dB
- Received Signal Level
- -58.29 dBm
- Effective Isotropic Radiated Power
- 48.5 dBm
- Link Assessment
- Carrier-grade — the link will ride out heavy weather
Step by step
- 1Values used
- 2Point-to-Point Link
- 3Regulatory EIRP
- 4Fade Margin= 26.7 dB
- 5Free-Space Path Loss= 129.29 dB
- 6Received Signal Level= -58.29 dBm
- 7Effective Isotropic Radiated Power= 48.5 dBm
- 8Link Assessment= Carrier-grade — the link will ride out heavy weather
Assumptions and limits
- The result is derived only from the 8 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or fees or charges into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Point-to-Point Link calculated?
FSPL = 20·log10(d_km) + 20·log10(f_MHz) + 32.44; received level = Tx power + antenna gains − cable losses − FSPL − misc losses; fade margin = received level − sensitivity. Free-space path loss grows 6 dB for every doubling of distance and 6 dB for every doubling of frequency. Adding transmitter power and antenna gain, then subtracting every loss along the path, gives the level arriving at the receiver; the difference from its sensitivity is the fade margin.
Why does Point-to-Point Link matter?
A link that closes with 3 dB of margin works on the day you commission it and drops during the first heavy rain, so margin — not raw signal level — is the number that decides whether the hop is production-ready.
What values do I need to enter?
This calculator takes 8 inputs: Link distance, Frequency, Transmit power, Transmit antenna gain, Receive antenna gain, Cable and connector loss per end, Rain, foliage and misc losses, Receiver sensitivity. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.