 Hey everybody, it's Tossos with RF Elements, and today we'll be talking about what's gain. Talking about DBI versus DBM versus DB. So one of the most important parameters of an antenna is its gain. Gain says how strongly an antenna radiates in any direction in free space. Gain is measured in units called decibels. A decibel is a unit of measure on the logarithmic scale, which is very useful when numbers shown differ by orders of magnitude. So let me explain this because a DB scale is often a huge misunderstanding amongst users. The range of 3 dB on the logarithmic scale means double the energy on a linear scale. Zero dB of gain, let's say, is one unit of linear scale. And 3 dB would be two units, 6 dB would be four units, and so on. 15 dB a gain would mean 32 units. Still manageable, right? Well, let's look at 30 dB a gain would be about 1,000 units, and 45 dB a gain would be equal to 31,622 units. So instead of working with magnitudes of multiples of tens of thousands, we use a logarithmic scale. So we can use much smaller numbers. But remember, a difference between 30 dB and 15 dB is not two times, it's 32 times the energy. DB simply compares signal intensity to a specific reference value. It must always be clear what that specific reference value is. DB without a suffix is used when dimensionalist numbers are compared. DB with a suffix is used for variables with a reference value, like power and watts. Antenna gain is usually given in DBI, where the I stands for isotropic. This means the intensity of the signal radiated by an antenna is compared to an isotropic antenna. Isotropic antennas is a theoretical antenna that radiates equally in all directions. So many people, including myself, often say antenna gain is 24 dB. This is typically incorrect since an antenna gain is measured in DBI units. RF videos have a range of power that they can deliver measured in DBM. Here the M stands for milliwatt, that means the power is in decibels compared to a milliwatt. Here 10 milliwatt corresponds to 10 dBm, 100 milliwatt to 20 dBm, 1000 milliwatt to 30 dBm, and so on. In datasheets, the gain of an antenna is usually given as a single number. This is the peak gain of the main lobe at a certain frequency, which is often misinterpreted as the most important of the various gain values. In reality, gain changes with angle and also with frequency. It's impossible to describe gain as a single number, and it's largely inaccurate to judge antenna based on its peak gain alone. More on this topic and others in our following videos.