Wireless Link
Compute the point-to-point RF link budget: free-space path loss (FSPL), EIRP, received level (RSSI), fade margin and the radius of the first Fresnel zone with the recommended 60 % clearance. All in your browser.
Fresnel zone (1st) at the midpoint
Keep at least 60 % of the 1st Fresnel zone clear to avoid
degrading the link.
How it is calculated · link budget and Fresnel
1. FSPL(dB) = 20·log₁₀(d_km) + 20·log₁₀(f_MHz) + 32.44.
Free-space propagation loss.
2. EIRP(dBm) = Tx + gain_Tx − cable_Tx.
Equivalent isotropically radiated power.
3. Prx(dBm) = EIRP − FSPL + gain_Rx − cable_Rx − extra.
This is the estimated RSSI at the receiver.
4. Margin(dB) = Prx − sensitivity.
>10 dB good, 0–10 dB tight,
<0 no link.
5. Fresnel zone (radius at the midpoint):
r = 8.66·√(d_km / f_GHz) meters; clearing the
60 % (0.6·r) is recommended.
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