The calculation method of wireless communication distance in free space propagation is given here: the so-called free space propagation refers to the radio wave propagation in infinite vacuum around the antenna, which is the ideal propagation condition. When a radio wave travels in free space, its energy is neither absorbed by an obstacle, nor reflected or scattered.

Communication distance is related to transmitting power, receiving sensitivity and operating frequency

(Lfs) (dB) = 32.44 + 20 LGD (km) + 20 LGF (MHz)

Where, Lfs is the transmission loss, D is the transmission distance, and the frequency unit is calculated in MHz.

As can be seen from the above equation, the propagation loss (also called attenuation) of radio waves in free space is only related to the working frequency F and propagation distance D. When f or D are doubled, [Lfs] will increase by 6dB respectively.

The following formula shows the loss of radio wave propagation in free space

Los = 32.44 + 20lg d(Km) + 20lg f(MHz)

Los is the propagation loss, in dB

D is distance in Km

F is the operating frequency in MHz

The following examples illustrate the propagation distance of a system with an operating frequency of 433.92mhz, transmission power of +10dBm(10mW) and receiving sensitivity of -105dbm in free space: 1. From transmitting power +10dBm, receiving sensitivity is -105dbm Los = 115dB 2. Calculated by Los, f d = 31 kilometers This is ideally transmission distance, will be lower than the value in practical application, this is because the wireless communication under the influence of various external factors, such as atmosphere, blockage, loss caused by multipath, etc, will be the loss on the reference value for the type, can calculate the approximate distance of communication. Assuming that the loss caused by atmosphere and shelter is 25dB, the communication distance can be calculated as d = 1.7km

Where does the antenna gain come from

In the gain index system of antenna, the reference value of gain index DBI (0DBI) is simply the characteristic value of pointing radiation source omnidirectional uniform radiation. It can be understood that the gain of the ideal antenna with omnidirectional radiation characteristics is 0(DBI). The different forms of omnidirectional antennas are only efforts to obtain ideal radiation characteristics under different conditions, that is to say, the gain of an antenna with omnidirectional uniform radiation characteristics cannot be greater than 0dbI.

Looking at another antenna gain index DBD (usually called DB), 0DBD =2.15 dbI, which means that an antenna with 0dbD gain has 2.15 dbI! So where does the antenna gain come from? Let's look at the benchmark definition of antenna gain index DBD: the gain value of ideal horizontal dipole antenna in the maximum radiation direction is 0DBD.

According to the directional characteristics of the horizontal dipole antenna, it is easy to see that its gain comes from the loss of omnidirectional performance, or simply called the concentration of radiation energy. Where does the gain of the vertical omnidirectional high gain antenna come from? The concentration of radiation energy from the vertical direction to the horizontal direction, that is to say, the omnidirectional vertical (erection type) antenna with gain should strictly be called the horizontal omnidirectional radiation antenna. The high directivity of yagi antenna with high gain characteristics reflects the contribution of energy concentration to antenna gain.

The improvement of antenna performance comes from two aspects, one is to improve the effective radiation performance of the antenna, the other is to make the radiation energy of the antenna as much as possible in the direction of the connected object. It can be said simply and definitively that the gain of the antenna (relative to 0dbI) comes from the concentration of radiated energy.