dBi to dBd CONVERSION
dBi is the gain of an antenna in relation to the gain of an isotropic antenna taken as reference (antenna radiating the same power towards any direction of the space), both fed with the same power. This is the gain usually indicated in the technical specifications by the manufacturers.
dBd is the gain measured when it is used a half-wave dipole as a reference. This gain is always below the dBi
The relation between both gains is: N dBi = N dBd + 2.15; or N dBd = N dBi - 2.15
For example: a 8 dBd gain antenna features 8+2.15 = 10.15 dBi