Decibels Demystified

Some of my students get rather confused with this so I thought a hint sheet may help: 

dBi: Gain verses Isotropic resonator. An isotropic antenna is a small antenna with no feed in free space which radiates well in all directions

dBd: Gain verses a Reference Dipole with a classic donut pattern of radiation.dBd = DBi + 2.15dB

ERP : Effective Radiated Power, the real numbers to concern yourself with when building antennas.

Gain: uses a log 10 scale

• 3dB = 2 fold improvement
• 6dB = 4 fold improvement
• 10dB = 10 fold improvement
• 20dB = 20 fold improvement