Antenna gain is not an easy notion for a new radio operator to pick up. Some even go as far as supposing that the antenna gain shows the increase in radio power.
But is not that the actual energy radiated is increased by the better antenna, this is not allowed by the law of the conservation of energy. It is because the radiated energy is handled, shaped-formed and directed better towards you.
A look at wikipedia tells us: ” In electromagnetics, an antenna’s power gain or simply gain is a key performance number which combines the antenna’s directivity and electrical efficiency. In a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction. In a receiving antenna, the gain describes how well the antenna converts radio waves arriving from a specified direction into electrical power.”
Now this explanation is correct but let’s make it simpler.
One can easily assume that an antenna radiates its energy all around, in a spherical pattern that is. But what actually happens is that different antenna designs manipulate the spherical pattern of the energy/radiation differently.
Thus we can push more energy in the preferred direction and increase the range in that direction
Here is a representation of four antenna patterns. The first is of a theoretical antenna, the second is of a 0 gain antenna (i.e. a 1/4 ground-plane antenna), the third is of a dipole antenna, and the fourth is off a high gain antenna like the vehicle mounted antennas, and J-poles.
Image Source: unknown
I call this the “Donut Effect”. Crush your donut and it will spread and take more area on the place. But crushing it will decrease its height and coverage on the upwards and downwards direction.
And for good measure here is what the pattern of a direction -i.e. Yagi- antenna
As expected there are practical implications and disadvantages when using a high gain antenna. You know, win some loose some. Making the antenna radiation disk (pattern) too thin may be a disadvantage when we need an antenna to reach all spots of rough terrain.
This picture says it all.
Now there are not many mobile antennas that have a 6 db gain, and the high gain are usually the longer ones, nevertheless the concept should to be kept in the back of your head.
And maybe a second antenna kept in the trunk…