Function free_space_loss_db 

pub fn free_space_loss_db(distance_m: u32, frequency_hz: u32) -> Decibels

Returns the free-space basic transmission loss between isotropic antennas, in dB.

This is Recommendation ITU-R P.525-5, equation (5), 20 log10(4 pi d / lambda): the loss with nothing in the way, which grows by 6.02 dB each time the distance doubles. Equation (6) writes the same loss in megahertz and kilometers as 32.4 + 20 log10 f + 20 log10 d, rounding its constant down from 32.45, so it reads about 0.05 dB low. A path near the ground loses more once terrain enters the first Fresnel ellipsoid, which fresnel_radius_mm sizes.

Arguments

• distance_m - the distance between the antennas in meters; 0 counts as one meter.
• frequency_hz - the carrier frequency in hertz; 0 counts as one hertz.

Returns

The loss in dB. The formula assumes the antennas sit in each other’s far field, many wavelengths apart.

Examples

use pamoja_lora::budget::free_space_loss_db;

assert_eq!(free_space_loss_db(1_000, 868_100_000).to_string(), "91.22");
assert_eq!(free_space_loss_db(2_000, 868_100_000).to_string(), "97.24");