The antennas are the transducers that convert electrical signals into electromagnetic waves and vice versa. In the same way as in high fidelity audio, where the loudspeakers quality is one of the most important issues, the quality of the antennas is critical to achieve a good wireless video link.
The quality of a link depends on several factors:
- Transmission power: The higher the power of the transmitter, the higher the received signal level for a given distance, or greater distance we can reach. In order to double the distance, we need to multiply by 4 the power of the transmitter.
- Receiver Sensitivity: It indicates the minimum signal level needed at the receiver for proper reception.
- Distance between transmitter and receiver: The greater the distance, the lower the level of received signal. Doubling the distance involves dividing by 4 the received signal level.
- Noise Floor: The level of electromagnetic noise present in the transmission frequency determines the quality of the link. If the receiver picks a noise level of potency similar to that of the received signal, the reception can never be good, even with a high sensitivity.
- Gain of transmitting antenna: The higher the gain, the highest signal level reaching the receiver. Given that the transmitter in FPV is in motion, usually the transmitting antenna is omnidirectional, with very low gain.
- Gain of the receiving antenna: the higher the gain, the highest signal level will capture the receiver. However, the gain is directly related to the directivity of the antenna. This means that high gain antennas are very directive, which requires keeping them oriented towards the aircraft.
The reality is that in FPV most of the parameters are fixed (transmitter power, receiver sensitivity), so the right choice of antennas is the factor that can help to increase the quality or the length of the link.
The following sections explain some of the fundamental parameters that define the performance of an antenna.