The Effect of Gain and Loss
Using a high gain antenna has the following effects at the transmitter:
- Increases the effective transmission power in certain directions, and reduces the power in others.
- Gain compensates for loss in coaxial cable.
- Makes the antenna more directional at the transmitter – a good effect for reducing unwanted RF radiation in non-required directions.
RF power generated by a transmitter is initially reduced by the coaxial cable, and then increased by the antenna gain.
Note: Care must be taken that the final effective radiated power is less than the regulated amount. In some countries, there are limits on the gain of antennas, as well as the final ERP.
At the receiver, high gain antennas have the following effects:
- Increases the received signal from certain directions, and reduces the signal from others. Gain will also increase the received external noise. If the increased noise exceeds the sensitivity of the receiver, then the gain improvement has been negated – that is, in noisy environments, antenna gain can have little effect at the receiver, but in no-noisy environments, it can.
- Gain compensates for loss in coaxial cable.
- Makes the antenna more directional – good effect for reducing unwanted RF noise in non-required directions, but a bad effect if you are relying on reflected signals from various directions.