What is antenna tracking ?
Antenna tracking is used in FPV to direct the video receiver antenna at the aircraft as it flies around the sky.
Why do we use it ?
We use it for a few reasons. One reason is antenna gain. With different types of antenna they all have different characteristics. One of the characteristics is its gain. The higher a gain of a receiver antenna the further out it will pick up a signal. But with this advantage comes a disadvantage of it needing to be pointed towards the aircraft. On the ground if you use a high gain antenna and it is not pointed at the aircraft to a degree then the picture is lost. The higher the gain of the antenna the more critical this becomes. Another consideration is polarization. If you were to say use a Circular Polarized antenna, the antenna has higher gain than a omni or rubber duck. But with this it still needs to be in the general direction of the plane. The advantage of this type of antenna is that it has low signal loss in banked turns and rolls. So to use the advantages of the higher gain or Circular Polarized antennas you need a way of pointing them at the plane as is flies while you have the goggles on flying it. Enter the antenna tracker.
So why don’t we just use omni antennas and not have to worry ?
With an omni antenna you have a gain of 3dbi ( normally less. ) This limits the range we can fly and being linear in polarization some or all signal can be lost while performing banked turns or acrobatics of any kind. With a Circular Polarized patch this is not the case with maneuvers, with a high gain antenna the range is not a problem anymore.
What does a tracker do ?
The antenna tracker uses information collected to physically move the antenna on the pan and tilt axis to have a direct path to the plane.
How does it work ?
There are a few systems available. Even some DIY systems.
Commercial systems
The main systems commercially available use data sent to them from the plane as it flies. This is in the form of telemetry. On starting up the plane the GPS coordinates of the plane are stored as “Home” this is a reference point for the trackers location. Then as the plane flies it relays the positional data of the plane to the tracker, the tracker then works out which direction and height the plane is from the “Home” reference and can point to the plane and track it in the sky. The data is sent normally in one of two ways, either down the audio channel from the plane or the video channel encoded into the signal. The tracker monitors this and extracts the telemetry and processes it before commanding the servos that control the pan and tilt axis of the antennae to move.
DIY systems
On a recent DIY system invented by IBCrazy, the system uses three antennas, two compare the RSSI signal from the plane. The higher the RSSI signal ( Receiver Signal Strength Indication ) the more the antenna turns to that direction ( either left or right ) until they are both equal. This then means the antenna directly in the middle is now pointing directly at the plane at all times. The system seems to work very well. It is limiting in its size, being that three antennas are needed. In both cases what you have is a directional antenna pointing at the plane at all times giving you the best possible signal for video, and the best signal for the tracker at the same time. The commercial units all use GPS to work, the DIY version does not need this. Both however depend on a signal being received, if no signal is being received the tracker will stop. So it is not ever 100% perfect. They do however open up a much more flexible way of flying and video enjoyment you can get