Radio transmissions use radio frequencies (RF) to transmit information. There are many different radio frequency ranges in the electromagnetic spectrum that are assigned to different services. From 800 MHz to 2.5 GHz , range of the electromagnetic spectrum, is used for various services such as digital cordless phones, pagers, personal digital assistants, laptops and personal computer memory card international association (PCMCIA) , and so on. Wireless communication takes place over free space through the use of radio frequency (RF) signals, that one device, the transmitter, sends RF signals to another device, the receiver. The transmitter can contact the receiver at any and all times, as long as both devices are tuned to the same frequency (or channel) and use the same scheme to carry the data between them. To send data across a wired link, an electrical signal is applied at one end and carried to the other end. The wire itself is continuous and conductive, so the signal can propagate rather easily. A wireless link has no physical strands of anything to carry the signal along.