dBi stands for decibel isotropic. It is the gain of an antenna relative to that of a theoretical isotropic antenna.
An Isotropic antenna radiates energy equally in all directions. By contrast a directional antenna focuses energy in a particular direction.
Use this Calculator to find the Antenna dBi Gain using:
- Antenna Factor (dB/m)
Gain (dBi) = 20*Log10(9.73/(λ*(10)AF/20))
- λ = Wavelength = c/f, where c is the speed of light and f is the frequency
- AF = Antenna Factor
The higher the dBi, the more focused the energy and the higher the antenna gain. Helium hotspot owners use high gain antennas to focus in a direction with larger numbers of witnesses.
Many TV antennas are of the directional Yagi Uda type and can be pointed in the direction of the transmitting tower for better signal reception.