Radio¶

This section describes how radio links works.

Link budget¶

Link budget defines how far your signal can go taking into account powers, gains, and losses.

Here is the equation $$ P_{RX} = P_{TX} + G - L $$

Where:

$P_{RX}$: Received Power
$P_{TX}$: Transmitter Output Power
$G$: Total Gains (Antennas, amplifiers)
$L$: Total Losses (Cables, distance, obstacles)

For a transmission to be received, the $P_{RX}$ must be greater than the receiver sensitivity.

Radio waves¶

Officially, radio wave are electromagnetic waves between 3 Hz and 3 GHz. Between 3 GHz and 300 GHz it's microwave. However, 5 GHz Wi-Fi is still considered as radio waves.

The energy of a photon in an electromagnetic wave is : $$ E = h \cdot f $$

Where:

$E$: The energy of the photon in Joules ($J$)
$h$: The Planck constant in $J\cdot s$
$f$: The frequency in Hz ($s^{-1}$)

The frequency and the wave length are linked according to this equation: $$ c = \lambda \cdot f $$

Where:

$c$: The celerity of the light ($m \cdot s^{-1}$)
$\lambda$: The wave length in meter ($m$)
$f$: The frequency in Hz ($s^{-1}$)