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March 6, 2020 22:58
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Simple link budget calculation for near sea level links
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| import math | |
| C_ms = 2.99792458e8 | |
| def db2times(db): | |
| return 10**(db/10.) | |
| def times2db(times): | |
| return 10 * math.log10(times) | |
| def free_space_path_loss_db(freq_hz, distance_m): | |
| return times2db(((4 * math.pi * distance_m * freq_hz) / (C_ms)) ** 2) | |
| def sea_level_oxygen_attenuation_db_km(freq_hz): | |
| "valid up to 57Ghz" | |
| f = freq_hz / 1e9 | |
| return (7.19e-3 + 6.09/(f**2 + 0.277) + 4.81 / ((f-57)**2 + 1.5)) * f**2 * 1e-3 | |
| def sea_level_water_vapour_attenuation_db_km(freq_hz, vapour_concentration_g_m3=7.5): | |
| f = freq_hz / 1e9 | |
| p = vapour_concentration_g_m3 | |
| return (0.050 + 0.0021 * p + 3.6/((f-22.2)**2 + 8.5) + 10.6/((f-183.3)**2 + 9) + 8.9/((f-325.4)**2+26.3)) * f**2 * p * 1e-4 | |
| def gas_atmospheric_loss_db(freq_hz, elevation): | |
| troposphere_height_km = 20 | |
| att_freq_km = sea_level_water_vapour_attenuation_db_km(freq_hz) + sea_level_oxygen_attenuation_db_km(freq_hz) | |
| total_att_km = att_freq_km * (1./math.sin(elevation * 3.1415 / (2*90.))) * troposphere_height_km | |
| return total_att_km | |
| def calc_EIRP_dbm(tx_amplifier_power_dbm, tx_antenna_peak_gain_dbi, tx_circuit_loss_db): | |
| return tx_amplifier_power_dbm + tx_antenna_peak_gain_dbi - tx_circuit_loss_db | |
| def calc_channel_loss(freq_hz, distance_km): | |
| free_space_loss_db = free_space_path_loss_db(freq_hz, distance_km * 1e3) | |
| atmospheric_loss_db = gas_atmospheric_loss_db(freq_hz, distance_km) | |
| channel_loss_db = atmospheric_loss_db + free_space_loss_db | |
| return channel_loss_db, free_space_loss_db, atmospheric_loss_db | |
| def link_budget_calc_with_rx_req_signal_dbm(freq_hz, distance_km, tx_antenna_peak_gain_dbi, | |
| tx_circuit_loss_db, tx_amplifier_power_dbm, | |
| rx_antenna_peak_gain_dbi, rx_cable_loss_db, antenna_pointing_loss_db, | |
| antenna_polarization_loss_db, | |
| rx_req_signal_dbm): | |
| # transmiter | |
| EIRP_dbm = calc_EIRP_dbm(tx_amplifier_power_dbm, tx_antenna_peak_gain_dbi, tx_circuit_loss_db) | |
| # channel loss | |
| channel_loss_db, free_space_loss_db, atmospheric_loss_db = calc_channel_loss(freq_hz, distance_km) | |
| # receiver | |
| carrier_power_antenna_output_dbm = EIRP_dbm - channel_loss_db + rx_antenna_peak_gain_dbi - antenna_pointing_loss_db - antenna_polarization_loss_db | |
| receiver_power_dbm = carrier_power_antenna_output_dbm - rx_cable_loss_db | |
| margin_db = receiver_power_dbm - rx_req_signal_dbm | |
| results = { | |
| "margin_db": margin_db, | |
| "EIRP_dbm": EIRP_dbm, | |
| "receiver_power_dbm": receiver_power_dbm, | |
| } | |
| return results | |
| results = link_budget_calc_with_rx_req_signal_dbm( | |
| freq_hz=5.1e9, | |
| distance_km=45, | |
| tx_antenna_peak_gain_dbi=30, | |
| tx_circuit_loss_db=2, | |
| tx_amplifier_power_dbm=28, | |
| rx_antenna_peak_gain_dbi=30, | |
| rx_cable_loss_db=4, | |
| antenna_pointing_loss_db=1.5, | |
| antenna_polarization_loss_db=2, | |
| rx_req_signal_dbm=-70) | |
| print(results) |
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{'margin_db': 8.616408368861357, 'EIRP_dbm': 56, 'receiver_power_dbm': -61.38359163113864