Once the radio’s frequency is chosen based on the legal regulations, the radio type and modulation method can be chosen. The two most common types of modulation for RKE devices are On-Off-Key (OOK) and Frequency Shift Key modulation (FSK). OOK modulation that represents a logic ‘1’ by turning the RF carrier on and a logic ‘0’ by turning the RF carrier off. This method of modulation requires few components and is inexpensive to implement, but it is highly prone to interference from external sources. FSK modulation is a type of modulation in which a logic ‘1’ is represented by a carrier at one frequency and a logic ‘0’ is represented by a carrier at another frequency. The advantage of FSK is that since the carrier is never turned off, the receiver can lock onto the transmitted signal, making the system more immune to external interference. The disadvantage is that it is more complicated and more expensive to implement and will not offer the range improvement in countries that average output power. Since most remote control / RKE transmissions do not require highly robust links but are cost sensitive, most products use an OOK radio.