Frequency is measured in Hertz (cycles per second) and radio frequencies are measured in kilohertz (KHz or thousands of cycles per second), megahertz (MHz or millions of cycles per second) and gigahertz (GHz or billions of cycles per second). Higher frequencies result in shorter wavelengths. The wavelength for a 900 MHz device is longer than that of a 2.4 GHz device.

In general, signals with longer wavelengths travel a greater distance and penetrate through, and around objects better than signals with shorter wavelengths.

The RF communication system then utilizes this phenomenon by wiggling electrons in a specific pattern to represent information. The receiver can make this same information available at a remote location; communicating with no wires.

In most wireless systems, a designer has two overriding constraints: it must operate over a certain distance (range) and transfer a certain amount of information within a time frame (data rate). Then the economics of the system must work out (price) along with acquiring government agency approvals (regulations and licensing).

• dB - Decibels
  Decibels are logarithmic units that are often used to represent RF power. To convert from watts to dB: Power in dB = 10* (log x) where x is the power in watts.
  Another unit of measure that is encountered often is dBm (dB milliwatts). The conversion formula for it is Power in dBm = 10* (log x) where x is the power in milliwatts.
   
• Line-of-site (LOS)
  Line-of-site when speaking of RF means more than just being able to see the receiving antenna from the transmitting antenna. In, order to have true line-of-site no objects (including trees, houses or the ground) can be in the Fresnel zone. The Fresnel zone is the area around the visual line-of-sight that radio waves spread out into after they leave the antenna. This area must be clear or else signal strength will weaken.

There are essentially two parameters to look at when trying to determine range.

• Transmit Power
  Transmit power refers to the amount of RF power that comes out of the antenna port of the radio. Transmit power is usually measured in Watts, milliwatts or dBm. (For conversion between watts and dB see below.)
   
• Receiver sensitivity
  Receiver sensitivity refers to the minimum level signal the radio can demodulate. It is convenient to use an example with sound waves; Transmit power is how loud someone is yelling and receive sensitivity would be how soft a voice someone can hear. Transmit power and receive sensitivity together constitute what is know as “link budget”. The link budget is the total amount of signal attenuation you can have between the transmitter and receiver and still have communication occur.

Example:
TX Power: 20dBm
RX Sensitivity: -110dBm
Total Link budget: 130dBm.

For line-of-site situations, a mathematical formula can be used to figure out the approximate range for a given link budget. For non line-of-site applications range calculations are more complex because of the various ways the signal can be attenuated.

At certain power levels some regulatory agencies require some form of spread spectrum. Spread spectrum can either be done by frequency hopping or by direct sequence. Frequency hopping consists of rapidly moving from one channel to the next while maintaining synchronization with the receiver. Direct Sequence is more complex, but works by slicing the carrier up with a code that can be decoded at the other end. Wireless Integrated radios uses frequency hopping as its method of spread spectrum.