Control System Range

All aircraft of any type use communications systems between the aircraft and the ground using radio frequency (RF). Some use cell phone connections, some direct RF. Most use one or more RF links (not cellular at this time). Those RF links are very susceptible to interference. The FCC limits their power to 1 watt, but most use far less than this amount of power. The transmission range in perfect conditions is about 3 miles. That is over water or flat land with little vegetation. It is very easy to lose communications (coms) as soon as the aircraft goes out of the line of sight. Going to the other side of a row of trees or tall buildings can cause loss of coms at just 100 yards.

There are long range systems available which have much longer range, up to 100 miles. These also are susceptible to the terrain, vegetation and buildings, but they are much improved. These are typically not used today because the FAA regs state that the aircraft must stay within line of sight (LOS).

These long-range systems employ three methods to increase range:

• Lower frequency – usually on 433 MHz instead of 2.4 GHz. Not only is 433 MHz lower which allows it to bend more easily around obstacles, but it is less crowded than 2.4 GHz. 2.4 GHz is used for cell phones, cordless phones, garage door openers, laptops, tablets, baby monitors and much more.
• More power – The FCC allows up to 1 watt for this type of use. Most drones use less than this to conserve battery power.
• Better antennas – The lower freq. 433 MHz uses an antenna which is much longer than the 2.4 GHz. High gain antennas such as Zagi, Helical, and Patch are used. These are directional antennas, so they must be pointed at the drone, if not, the signal is gone. So, most times they also combine the directional antenna with an antenna tracker which points the antenna to the direction of the drone automatically using the data from the ground station to identify where the drone is and relay that to the tracker.