If a standard is chosen for the application, then the standards frequently define the physical radio that is used with them. Otherwise, a radio type is typically used with a standard and that is what will be available. If a proprietary protocol is chosen, then there are some further considerations before a radio is chosen. First there are legal considerations defined by the regulatory agencies in the countries where the product will be used. Two major regulatory agencies are the FCC in the United States and ETSI in Europe. Most other countries tend to follow one or the other with relatively minor differences. Both of these agencies have defined general use radio frequency bands, called unlicensed or ISM bands, where the equipment must meet certain technical requirements but the end user does not need a license to operate the device. The best place to start is to define the type of data that is to be transmitted. Frequencies in the 300MHz to 400MHz range are set aside for command and control signals, like remote control. These bands are heavily regulated, but that tends to make them more free of interference. Frequencies in the 900MHz range in North America and 860MHz range in Europe are for general use. There are no regulations on the type of data or how often it can be transmitted, just technical requirements on the transmitter output power and harmonic levels. Frequencies in the 2.45GHz range are generally accepted by all countries with very few exceptions. This allows one product to be manufactured and sold globally. The down side is that the range tends to be much lower than at other frequencies and power consumption tends to be higher. Once the frequency is selected, the modulation method can be evaluated. For remote control applications in the 400MHz range, OOK is used almost exclusively. This type of modulation results in inexpensive and relatively uncomplicated radios and offers a range advantage in countries that average output power over time. For the 900 MHz range, FSK is most common. These bands also allow for higher power spread spectrum radios, which are more complicated and expensive, but offer longer range and greater reliability. It is ultimately the designer’s responsibility to understand the applicable regulations and select a radio appropriate for the product.