Wireless PtP Link Budget & Fresnel Zone Calculator

Calculate received RX signal (dBm), free-space path loss FSPL, 60% Fresnel clearance, earth curvature bulge, and minimum triangle tower heights.

Input Parameters

Try Example:

Calculation Results

distKm: 5
freqGhz: 5.8
txDbm: 24
antGainDbi: 23
obstacleM: 12
cableConnLossDb: 2
fsplDb: 121.7
rxSignalDbm: -53.7
fresnelRadiusM: 8.04
clearance60PctM: 4.82
earthBulgeM: 0.37
minTowerHeightM: 18
recTriangleStages: 5
linkQuality: SANGAT STABIL (Full Modulation 8x / 256-QAM)
linkQualityEn: EXCELLENT (Full Modulation 8x / 256-QAM)
summaryText: Ringkasan Wireless PtP Link Budget & Fresnel Zone – InfraCalc.id Jarak Tembak : 5 km pada Frekuensi 5.8 GHz (FSPL: 121.7 dB) Radio & Antena : TX 24 dBm + 2× Antena Dish 23 dBi Estimasi RX : -53.7 dBm (SANGAT STABIL (Full Modulation 8x / 256-QAM)) Fresnel Zone 1 : Radius 8.04 m (Wajib bebas halangan minimal 60% = 4.82 m + Lengkung Bumi 0.37 m) Tinggi Tower : Minimal 18 Meter di atas tanah (dengan tinggi pohon/gedung tengah 12 m)

How to Use This Tool

Enter the straight-line link distance in kilometers (km) and specify the radio carrier frequency (e.g. 5.8 GHz, 2.4 GHz, or 24/60 GHz).
Input transmitter launch power (dBm), directional dish antenna gain (dBi), and peak midpoint obstruction height above ground.
Review the predicted received signal level (RX in dBm), link modulation health, 60% Fresnel radius, and minimum tower elevation heights.

Worked Example: Rural PtP Link 5 km @ 5.8 GHz (Dish 23 dBi)

Worked example: A 5 km link at 5.8 GHz using a 24 dBm transmitter paired with dual 23 dBi dish antennas yields a predicted RX signal of -53.7 dBm (EXCELLENT (Full Modulation 8x / 256-QAM)). Factoring in a 12m midpoint tree barrier, 0.37m earth curvature bulge, and 4.82m 60% Fresnel clearance dictates a minimum tower height of 18 meters (±5 triangular tower stages @4m).

Example Input

{
  "distKm": 5,
  "freqGhz": 5.8,
  "txDbm": 24,
  "antGainDbi": 23,
  "obstacleM": 12
}

Calculated Output

distKm:: 5
freqGhz:: 5.8
txDbm:: 24
antGainDbi:: 23
obstacleM:: 12
cableConnLossDb:: 2
fsplDb:: 121.7
rxSignalDbm:: -53.7
fresnelRadiusM:: 8.04
clearance60PctM:: 4.82
earthBulgeM:: 0.37
minTowerHeightM:: 18
recTriangleStages:: 5
linkQuality:: SANGAT STABIL (Full Modulation 8x / 256-QAM)
linkQualityEn:: EXCELLENT (Full Modulation 8x / 256-QAM)
summaryText:: Ringkasan Wireless PtP Link Budget & Fresnel Zone – InfraCalc.id Jarak Tembak : 5 km pada Frekuensi 5.8 GHz (FSPL: 121.7 dB) Radio & Antena : TX 24 dBm + 2× Antena Dish 23 dBi Estimasi RX : -53.7 dBm (SANGAT STABIL (Full Modulation 8x / 256-QAM)) Fresnel Zone 1 : Radius 8.04 m (Wajib bebas halangan minimal 60% = 4.82 m + Lengkung Bumi 0.37 m) Tinggi Tower : Minimal 18 Meter di atas tanah (dengan tinggi pohon/gedung tengah 12 m)

Core Concept & Engineering Notes

Designing long-range outdoor Point-to-Point (PtP) microwave wireless backhauls requires rigorous modeling of two fundamental physical phenomena: RF link power budgeting and spatial electromagnetic wave clearance (Fresnel Zone). A common engineering misconception presumes that an unobstructed visual optical line-of-sight (LOS) guarantees flawless microwave throughput. In reality, propagating radio waves expand into a three-dimensional elliptical corridor spanning transmitter and receiver apertures. The first Fresnel Zone represents the critical elliptical envelope wherein reflected secondary wavefronts constructively or destructively interfere with the direct line-of-sight signal. Global telecommunication standards mandate that at least 60% of the first Fresnel radius remain entirely free of terrain, tree canopies, or architectural obstacles. When physical incursions penetrate this 60% boundary, diffraction loss induces severe phase cancellation, crippling modulation rates regardless of clear visual visibility. Beyond ground obstructions, earth curvature bulge introduces severe elevation deflection over trajectories exceeding 5 kilometers. At path midpoint, the planetary arc bulges upward by (d²)/68 meters (producing 0.37 meters at 5 km and surging to 5.88 meters at 20 km). This tool models Free Space Path Loss (FSPL), transmitter launch power, directional parabolic dish gains, cable attenuation, earth curvature, and mandatory 60% Fresnel clearance to accurately predict received signal strength (RX in dBm) alongside required triangular lattice tower elevations.

How It Was Calculated (Formulas & Steps)

Mathematical Formulas

FSPL (dB) = 20 × log10(Dist km) + 20 × log10(Freq GHz) + 92.45
Received RX (dBm) = TX + Gain TX + Gain RX - FSPL - Cable Losses (2 dB)
1st Fresnel Radius (m) = 8.656 × sqrt(Dist km / Freq GHz)
60% Fresnel Clearance = Fresnel Radius × 0.60
Earth Curvature Bulge (m) = (Dist km²) / 68 at trajectory midpoint
Minimum Tower Height = ceil(Obstacle Height + Earth Bulge + 60% Fresnel Clearance)

Step-by-Step Calculation

1. Free Space Path Loss (FSPL): 20 × log10(5 km) + 20 × log10(5.8 GHz) + 92.45 = 121.7 dB
2. Received Signal Power (RX): 24 dBm (TX) + 23 dBi (Ant-TX) + 23 dBi (Ant-RX) - 121.7 dB (FSPL) - 2 dB (Loss) = -53.7 dBm [EXCELLENT (Full Modulation 8x / 256-QAM)]
3. 1st Fresnel Zone Radius: 8.656 × sqrt(5 / 5.8) = 8.04 meters
4. 60% Mandatory Clearance Zone: 8.04 m × 60% = 4.82 meters
5. Earth Curvature Bulge at Mid-point: (5²) / 68 = 0.37 meters
6. Minimum Antenna Tower Height: ceil(12 m obstacle + 0.37 m bulge + 4.82 m clearance) = 18 meters above ground
7. Triangle Tower Construction: ceil(18 m / 4m stage) = ± 5 triangular tower stages

Frequently Asked Questions (FAQ)

Why is the optimal outdoor wireless RX signal target between -50 dBm and -65 dBm?

Levels between -50 and -65 dBm permit modern radios to unlock highest constellation modulations (256-QAM or 1024-QAM / 8x to 10x data rates) while maintaining an essential 15–20 dB thermal fade margin during rain. Signals hotter than -40 dBm risk front-end receiver saturation, whereas readings below -75 dBm suffer carrier throttling.

What happens when more than 40% of the Fresnel zone is physically obstructed?

When obstacles intrude beyond 40% of the Fresnel radius (leaving less than 60% clearance), reflected electromagnetic waves arrive 180 degrees out of phase, destructively canceling the primary signal. This triggers severe multipath fading, heavy frame discards, and link degradation.

How do you bypass prominent hills or high-rise structures obstructing a PtP path?

Proven engineering remedies include: (1) Increasing tower elevations at both endpoints; (2) Re-siting antenna mounting masts laterally; or (3) Establishing an intermediate active repeater station (back-to-back PtP transceivers) atop the obstructing topography.

Why are 60 GHz and 24 GHz frequencies far more susceptible to rain fade than 5 GHz?

Millimeter-wave frequencies (e.g. 60 GHz with a 5 mm wavelength) match the physical dimensions of falling raindrops and atmospheric oxygen resonance bands. Rain droplets directly absorb and scatter the RF wavefront, limiting 60 GHz deployments to shorter hops (<2 km) paired with 5 GHz failover backup radios.

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References & Notes

Last updated: 2026-11-06Content Status: Draft (Pending Editorial Review)

Note: Results above are mathematical estimates based on standard formulas. Always verify against official vendor documentation and site conditions before production deployment.