Crashing a model aeroplane is sometimes due to a few minutes of uncontrolled flight. That’s usually all it takes to crash your expensive model and it can ruin your day! Flying remote control (RC) airplanes is an interesting hobby, but you have to be careful that your RC transmissions always get to the airplane so you are in control. Understanding some of the basic ways that signals can be blocked can keep your RC airplane safe and your hobby enjoyable.
Crossed frequencies - There are several frequencies (like 27 MHz, 49 MHz and 75 MHz) set aside for RC devices. If you are using one of these frequencies and someone nearby is using the same frequency, there will be interference. The RC vehicles can get the wrong signal or even a blending of the signals, and either could destroy your RC plane. The solution is to get a 2.4 GHz controller that uses Digital Spectrum Modulation (DSM). This technology was developed in World War II to control torpedoes, as it is hard to jam DSM transmissions. The frequency has many channels; a transmitter checks to see which channels are open, then locks it in place by establishing a code that becomes part of each transmission. A DSM receiver will only react to a signal that is preceded with the proper code. This system is used by all military transmissions and is the best way to protect your RC airplane.
Blocked Signal - Even if you are using a DSM system, your RC airplane will not react if it does not receive a transmission. Flying in a place where a building or other structure can block the signal will cause your airplane to be non-responsive. This is why RC airplanes should be flown in open spaces, like large fields. Even in an open space, the signal can be blocked by a part of the airplane (like the engine or landing gear) when the airplane is in certain positions in relation to the transmitter. One solution for the airplane blocking its own signal is to put two or more antennae in the airplane in such a way that one of the antenna will receive the signal no matter how the airplane is turned.
Spark Gap Generators - Spark gap generators are a primitive type of radio transmitter. Used in the early days when radio was being developed, they do not transmit on a particular frequency but broadcast on all frequencies at the same time. Whenever you have a spark jumping across a gap, you have a spark gap generator. All internal combustion engines--cars, trucks, real airplanes and many trains--are spark gap generators. They do not transmit any one frequency, but they can mask whatever frequency you are transmitting on. If a jumbo jet or military fighter flies over the area where you are flying your RC airplane, or even if a train goes by, your signal can be masked long enough to crash your RC model. Unfortunately, there is no way to avoid spark gap transmission interference except to avoid flying your RC airplane near rail lines or airports.