Radio frequency waves are part of the electromagnetic spectrum. Usage of radio frequency waves is strictly regulated by laws. We have all heard about telecom operators bidding for various spectrums. They are actually entering into an agreement with the governments around the world that they be allocated a particular band in the electromagnetic spectrum surrounding the earth. The governments in turn decide who will be allowed to use which band in the electromagnetic spectrum. Post allocation, a telecom operator can exclusively use the allocated band for their telecommunication operations. The same applies to radio station channels airing on particular radio frequencies.
There are various types of radio frequency waves depending upon their frequencies between the ranges of 3 KHz to 300 GHz. There is a special radio frequency that has been set aside worldwide, for use by the Industrial, Scientific and Medical (ISM) community. This is officially known as the 2.4 GHz ISM band. In this chapter, we will learn how to use 2.4 GHz RF chips for transmitting and receiving short range radio waves. Practically, short range would mean not more than 30-50 meters.
Typically, RF-based solutions use an RF capable chip or module together with a microcontroller. As shown in the preceding figure, at one end we have the transmitting device and at the other end we have the receiving device. In this chapter, we will use the Arduino board as the micro-controller board and the nRF24L01 transceiver chip as the RF transmitter as well as RF receiver. This concept is also known as Machine-to-Machine (M2M) communications: one microcontroller sends an RF encoded message to another microcontroller.
RF signals travel freely in the electromagnetic spectrum around us, in the air. The transmitted signals can be received by all RF receivers (apart from the intended recipient) in the vicinity of the transmitter. Hence the transmitted data can also be intercepted and received by anyone. In order to secure RF communications from unintended recipients, usually, RF signals are encrypted and they also require passwords.
For example, think of a home Wi-Fi router. A Wi-Fi router requires a password- without the password a connection to the router is not possible. But the Wi-Fi connection also warns us that "Information sent over this network might be visible to others". At the end of this chapter we will be able to appreciate why wireless data transfer is so vulnerable, unless protected.