RF link budget primitives.
Pure physics calculations with no system-specific assumptions. Combine these with Orbis geometry outputs (slant range, elevation) to build a complete link budget for your specific system.
Example: simple uplink budget
# Get geometry from Orbis
{:ok, elements} = Orbis.Format.TLE.parse(line1, line2)
{:ok, look} = Orbis.look_angle(elements, datetime, station)
# Compute path loss
fspl = Orbis.RF.fspl(look.range_km, 1616.0)
# Your system parameters
eirp_dbw = 27.0 + 3.0 - 30.0 # tx power + antenna gain - 30
gt_dbk = -12.0 # satellite G/T
other_losses = 3.0 # atmospheric, polarization, etc.
# Link margin
margin = Orbis.RF.link_margin(%{
eirp_dbw: eirp_dbw,
fspl_db: fspl,
receiver_gt_dbk: gt_dbk,
other_losses_db: other_losses,
required_cn0_dbhz: 35.0
})Summary
Functions
Carrier-to-noise-density ratio (C/N₀) in dB-Hz.
Antenna gain in dBi for a parabolic dish.
Effective Isotropic Radiated Power in dBW.
Free-space path loss in dB.
Link margin in dB.
Wavelength in meters for a given frequency.
Functions
Carrier-to-noise-density ratio (C/N₀) in dB-Hz.
C/N₀ = EIRP + G/T - FSPL + 228.6 - other_lossesThe 228.6 is the Boltzmann constant expressed as a positive number in the conventional link budget equation.
Parameters
eirp_dbw— transmitter EIRP in dBWfspl_db— free-space path loss in dB (fromfspl/2)receiver_gt_dbk— receiver figure of merit (G/T) in dB/Kother_losses_db— sum of all other losses (atmospheric, polarization, pointing, etc.)
Examples
iex> Orbis.RF.cn0(0.0, 165.0, -12.0, 3.0)
48.599999999999994Antenna gain in dBi for a parabolic dish.
G = 10·log₁₀(η · (π·D/λ)²)Parameters
diameter_m— dish diameter in metersfrequency_hz— frequency in Hzefficiency— aperture efficiency (default 0.55)
Examples
iex> Orbis.RF.dish_gain(1.0, 1616.0e6)
21.97903741903791Effective Isotropic Radiated Power in dBW.
EIRP = P_tx(dBm) + G_tx(dBi) - 30Examples
iex> Orbis.RF.eirp(27.0, 3.0)
0.0Free-space path loss in dB.
This is the inverse square law — signal attenuation over distance in vacuum. The foundational calculation in any link budget.
FSPL = 32.45 + 20·log₁₀(f_MHz) + 20·log₁₀(d_km)Parameters
distance_km— slant range to satellite in kmfrequency_mhz— carrier frequency in MHz
Examples
iex> Orbis.RF.fspl(1200.0, 1616.0)
158.20245204972383Link margin in dB.
Positive margin means the link closes. Negative means it doesn't.
Takes a map so parameters are self-documenting:
Parameters
:eirp_dbw— transmitter EIRP in dBW:fspl_db— free-space path loss in dB:receiver_gt_dbk— receiver G/T in dB/K:other_losses_db— sum of miscellaneous losses in dB:required_cn0_dbhz— minimum C/N₀ for demodulation in dB-Hz
Examples
iex> Orbis.RF.link_margin(%{
...> eirp_dbw: 0.0,
...> fspl_db: 165.0,
...> receiver_gt_dbk: -12.0,
...> other_losses_db: 3.0,
...> required_cn0_dbhz: 35.0
...> })
13.599999999999994Wavelength in meters for a given frequency.
Examples
iex> Orbis.RF.wavelength(1616.0e6)
0.1855151349009901