Real RF link-budget and orbital-access math: link margin, coverage footprint, and ground-station pass schedules driven by SGP4 propagation. The same physics as the heavy reference tools, lighter and owned.
Friis link budget with elevation-dependent losses
SGP4 ground-track, footprint & pass scheduling
Live waterfall + link margin across the full pass
This is a multi-panel console built for a desktop. Open it on a larger screen to run the live analyzer.
SGP4 / SDP4 (Simplified General Perturbations 4), the industry-standard analytic model for near-Earth satellites. Implemented via satellite.js (Vallado 2006 / Celestrak). Accounts for J2 oblateness, atmospheric drag (via B* drag term in TLE). Valid range: 200 to 2000 km circular orbits, short-arc predictions (days). Error: typically <1 km position error over 1 to 2 day arcs with fresh TLE.
C/N₀ = EIRP − FSPL − L_other + G/T + 228.6, standard RF link equation
Eb/N₀ = C/N₀ − 10·log₁₀(R_b), bit energy to noise density
Margin = Eb/N₀ − Required Eb/N₀, positive = link closes
Geometry
Slant range computed from spherical-Earth geometry (R_e = 6371 km) using satellite altitude and elevation angle. Footprint radius via the rigorous Earth-central-angle formula ρ = acos((R_e/(R_e+h))·cos(el)) − el, where the trailing − el is the local-horizon correction; omitting it (geocentric approximation) overstates the radius by a few percent at low mask angles. Accurate to <0.5% vs WGS-84 ellipsoid at LEO altitudes.
Loss Allowances (Simplified)
Atmospheric/gaseous: Per-band zenith allowance (UHF 0.1 dB, S 0.2 dB, X 0.3 dB, Ka 0.8 dB) scaled by slant-path airmass ≈ 1/sin(el) (clamped at 5° elevation to bound the horizon singularity), so low-elevation passes lose meaningfully more. Approximates ITU-R P.676; use the full model for operational analysis.
Rain attenuation: Conservative zenith allowance (UHF 0 dB, S 0.1 dB, X 0.5 dB, Ka 2.0 dB) likewise scaled by ≈ 1/sin(el) airmass. Actual depends on region and climate zone. Use ITU-R P.618 for fade-margin sizing.
Pointing & polarization: Fixed 0.5 dB combined. Actual depends on antenna system.
Pass Scheduling
Access windows computed by propagating SGP4 at configurable time steps, computing look angles (azimuth, elevation, range) to each ground station using Leaflet/satellite.js ecfToLookAngles, and recording intervals where elevation ≥ minimum mask angle.
Standard link-budget and SGP4 access math, the same physics as reference tools (STK/MATLAB), lighter and owned. Rain and atmospheric models use zenith allowances scaled by ~1/sin(el) airmass; verify against ITU-R P.618 / P.676 for operational use. TLE accuracy degrades beyond 1 to 2 days from epoch, so refresh TLEs for mission-critical scheduling.
For demonstration · Client guide
How to read this tool
What this is
The link-budget and orbital-access math a smallsat operator needs, all in the browser: will my signal close, where does the satellite cover, and when can my ground station talk to it.
What you're looking at
World map: the satellite's ground track, your ground stations, and the live coverage footprint; scrub through time to watch it move.
Link-budget waterfall (right): signal power built up step by step (transmit power → losses → received signal → margin). Green margin = the link closes; red = it doesn't.
Pass schedule (bottom): when each ground station can see the satellite (rise/set, duration, max elevation). Click a pass for its elevation-vs-time curve.
Inputs (left): orbit, RF band, antennas, and data rate. Change them and everything recomputes.
Try this
Load the Operator B preset, then lower the data rate and watch the margin go green.
On your engagement
We configure it to your spacecraft, bands, and ground network, lighter than the reference tools, and yours to keep.
Real vs. demonstration. Standard, verifiable physics (FSPL, C/N₀, SGP4), the same math as the heavy reference tools (STK/MATLAB), with a hand-checkable worked example. Atmospheric/rain models are simplified, as noted.
The Gideon Corp.