Line of sight clearance, obstacle analysis, and earth bulge correction for microwave, WISP, and terrestrial RF links. Compute first, second, and third Fresnel zone radii with k factor adjustable earth curvature and the industry 60 per cent F1 clearance rule.
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Line of sight is more than just a clear visual path between two antennas. RF energy travels not as a pencil beam but as an expanding ellipsoid called the Fresnel zone, with the direct ray running through the centre and a region of constructive and destructive interference around it. The first Fresnel zone is the ellipsoid where any reflection or diffraction would arrive at the receiver with a path length difference up to half a wavelength. Industry practice is to keep at least 60 per cent of the first Fresnel zone clear of obstructions for the link to behave as line of sight. Drop below that and diffraction loss starts to dominate the budget. Drop into the second Fresnel zone (50 per cent obstruction) and the link is materially degraded. Total obstruction puts the link into knife edge diffraction territory where the loss is large and unpredictable.
The noIM₃ Fresnel Zone Calculator computes the full ellipsoid geometry at any point along a path. Fn equals square root of (n times lambda times d1 times d2 divided by (d1 plus d2)) for any zone order n and any position along the path. The maximum radius sits at midpath. The 60 per cent F1 clearance line is rendered explicitly. Earth curvature is corrected with the standard effective earth radius model. h bulge equals d1 times d2 divided by (12.75 times k), where k is the refractivity factor (2 over 3 for sub refractive conditions, 1.0 for vacuum or no refraction, 4 over 3 for standard troposphere, 1.5 for super refractive, or any user defined value). Selectable k matches ITU R P.530 recommendations for troposphere propagation.
Path profile visualisation overlays the line of sight ray, first and second Fresnel ellipsoids, earth bulge, and user defined obstacles (trees, buildings, ridges, towers) so diffraction risk is immediately visible. Built in frequency band presets cover 6, 11, 15, 18, 23, 38, and 80 GHz microwave backhaul, 5 GHz ISM, 2.4 GHz WiFi, 900 MHz ISM, and 450 MHz UHF. The clearance dashboard returns pass, caution, or fail against the 60 per cent F1 threshold for every defined obstacle. Useful for microwave backhaul route feasibility, WISP and private LTE link planning, mast height optimisation, tree and building clearance assessment, and validation of terrain studies before site survey.
Computes Fn equals square root of (n times lambda times d1 times d2 divided by (d1 plus d2)) for any zone order n (F1, F2, F3) and any position along the path. Maximum radius at midpath. Radius at user selected offsets along the path. Scaled 60 per cent F1 clearance line rendered explicitly so the industry line of sight minimum is visible directly.
Configure obstacle height and position along the path. The calculator computes available clearance after earth bulge correction, expresses it as a percentage of F1, and reports pass (greater than 60 per cent F1), caution (40 to 60 per cent), or fail (less than 40 per cent) against the line of sight threshold. Useful for tree, building, ridge, and tower clearance checks during route feasibility assessment.
Earth curvature correction using the standard effective earth radius model. h bulge equals d1 times d2 divided by (12.75 times k) for distances in km and bulge in metres. Selectable k factor presets covering sub refractive (2 over 3), no refraction (1.0), standard troposphere (4 over 3), super refractive (1.5), and any user defined value. Matches ITU R P.530 recommendations for terrestrial line of sight propagation.
Render the full path profile with the line of sight ray, first Fresnel ellipsoid, second Fresnel zone, earth bulge curve, and any number of user defined obstacles overlaid. Obstacles are placed by distance and height and the calculator returns clearance per obstacle. Useful for ridge crossing assessment, tree line evaluation, and confirming whether mast height adjustments will achieve the 60 per cent F1 minimum.
Built in presets for 6, 11, 15, 18, 23, 26, 38, and 80 GHz microwave backhaul, 5 GHz ISM, 2.4 GHz WiFi, 900 MHz ISM, and 450 MHz UHF. Each preset populates frequency for the common configuration so the route feasibility check is one click. Manual entry remains available for unusual frequencies, millimetre wave, and sub GHz applications.
Interactive charts cover Fresnel radius versus position along the path, full path profile with obstacles overlaid, clearance versus frequency at the same path geometry (showing how higher frequency improves Fresnel clearance for the same physical clearance), and earth bulge versus k factor (showing how refractivity changes the effective bulge). Tables break down clearance at each zone order and at common percentage thresholds (60, 80, 100 per cent).
Maximum Fresnel radius at midpath is the headline number for path planning. The calculator additionally reports the radius at any user selected offset along the path, useful when the critical obstacle is not at the midpoint (a ridge near one end of the path, a tree line at a known offset, a tower or building at a measured distance from one site).
Single glance pass, caution, or fail status against the 60 per cent F1 line of sight threshold for every defined obstacle. Combined with the path profile visualisation, the dashboard makes route feasibility immediately obvious and supports the design discussion around mast height, route deviation, or alternative site selection.
Runs entirely in your browser. No path geometry, obstacle data, or link parameters are submitted to a server. Useful for commercially confidential infrastructure planning, defence and security site work, and environments where information security policy prohibits sending engineering data to third party services.
A Fresnel zone is an elliptical region around the direct ray between transmitter and receiver where any reflected or diffracted ray would arrive with a path length difference up to a particular fraction of a wavelength. The first Fresnel zone uses a half wavelength bound. The second uses a full wavelength. The third uses 1.5 wavelengths. The first Fresnel zone is the dominant contributor to the link, which is why industry practice is to keep at least 60 per cent of the first Fresnel zone clear of obstructions for the link to behave as line of sight.
Fn equals square root of (n times lambda times d1 times d2 divided by (d1 plus d2)), where n is the zone order, lambda is the wavelength, d1 is the distance from the transmit end to the point of interest, and d2 is the distance from that point to the receive end. Maximum at midpath where d1 equals d2 equals d over 2. The 60 per cent F1 line equals 0.6 times F1 at any point along the path.
It is the industry rule of thumb derived from theoretical analysis of diffraction loss as a function of obstruction depth. With less than 60 per cent F1 clearance, diffraction loss is essentially zero. Between 60 and 100 per cent F1 obstruction, diffraction loss is small but not negligible. At full F1 obstruction (touching the line of sight), the link is at knife edge and loss is around 6 dB. Beyond that, the link is in deep diffraction and loss grows quickly. The 60 per cent threshold is the practical line above which the link behaves as line of sight under typical atmospheric variation.
Earth bulge is computed using the standard effective earth radius model. h bulge equals d1 times d2 divided by (12.75 times k) for d1 and d2 in km and bulge in metres. The k factor accounts for atmospheric refraction. Standard troposphere is k equals 4 over 3, which extends the effective earth radius and bends the radio ray slightly. Sub refractive conditions (k around 2 over 3) shrink the effective radius and increase the apparent bulge. Super refractive conditions (k around 1.5) extend the effective radius. The calculator supports k presets covering all the common conditions plus user defined values.
Sub refractive conditions (k less than 1) occur when the troposphere refractivity gradient inverts, typically during temperature inversions and certain weather patterns. The apparent earth bulge increases, which can take a marginal link below the 60 per cent F1 threshold and produce diffraction loss that knocks the link out. Designing the link with k equals 2 over 3 (or worse) as a worst case confirms whether the route survives the bad atmosphere or only works under standard troposphere. ITU R P.530 is the reference for this practice.
Fresnel clearance is the first feasibility check on any microwave route. Pass the 60 per cent F1 rule against k equals 4 over 3 and the link is line of sight. Survive k equals 2 over 3 and the link is robust. Use the noIM₃ Link Planner for full ITU P.530 link design with terrain accurate path profiles from Mapbox global Terrain RGB DEM, automatic ITU model coverage (P.526, P.530, P.676, P.838, P.840, P.2108), and full provenance for every input. The Fresnel Zone Calculator covers fast feasibility. The Link Planner covers full design.
The maximum Fresnel radius is at midpath, but the critical obstacle is often not at the midpoint. The calculator returns Fresnel radius at any user selected offset along the path, so you can evaluate clearance against a tree line at 30 per cent of the path, a ridge at 70 per cent, or a building at a known distance. The pass or fail dashboard handles each obstacle independently against its position.
No. The calculator runs entirely in your browser. No path geometry, obstacle data, or link parameters are submitted to a server. Useful for commercially confidential infrastructure planning, defence and security site work, and environments where information security policy prohibits sending engineering data to third party services.
Free forever on a Standard account. No credit card.
