There are several categories of cellular telephone. Mobile units are mounted in a vehicle. Transportable units can be easily moved from one vehicle to another. Pocket phones, weighing in at less than 4 ounces, can be conveniently carried in a jacket pocket or purse. There are even cellular telephones that can be worn. Regardless of how they are packaged, cellular telephones consist of the same basic elements.

Handset/Keypad The handset and keypad provide the interface between the user and the system. This is the only component of the system with which, under normal operation, the user needs to be concerned. Any basic or enhanced system features are accessible via the keypad, and once a connection is established, this component provides similar handset functionality to that of any conventional telephone. Until a connection is established, however, the operation of the handset differs greatly from that of a conventional telephone. Instead of initiating a call by first obtaining a dial tone from the network switching system, the user enters the dialed number into the unit and presses the “Send” function key. This process conserves the resources of the cellular system, since only a limited number of talk paths are available at any given time. The “Clear” key enables the user to correct misdialed digits.

Once the network has processed the call request, the user will hear conventional call-progress signals such as a busy signal or ringing. From this point on, the handset operates in the customary manner. To disconnect a call, the “End” function key is pressed on the keypad. The handset contains a small illuminated display that shows dialed digits and provides a navigational aid to other features. The keypad enables storage of numbers for future use and provides access to other enhanced features, which may vary according to manufacturer.

Logic/Control The logic/control functions of the phone include the numeric assignment module (NAM) for programmable assignment of the unit’s telephone number by the service provider and the electronic serial number of the unit, which is a fixed number unique to each telephone. When a customer signs up for service, the carrier makes a record of both numbers. When the unit is in service, the cellular network interrogates the phone for both of these numbers in order to validate that the calling/called cellular telephone is that of an authentic subscriber. The logic/control component of the phone also serves to interact with the cellular network protocols. Among other things, these protocols determine what control channel the unit should monitor for paging signals and what voice channels the unit should use for a specific connection. The logic/control component is also used to monitor the control signals of cell sites so that the phone and network can coordinate transitions to adjacent cells as conditions warrant

Transmitter/Receiver The transmitter/receiver component of the cell phone is under the command of the logic/control unit. Powerful 3-watt telephones are typically of the vehiclemounted or transportable type, and their transmitters are understandably larger and heavier than those contained within lighter-weight handheld cellular units. These more powerful transmitters require significantly more input wattage than hand-held units that transmit at power levels of only a fraction of a watt, and they use the main battery within a vehicle or a relatively heavy rechargeable battery to do so. Special circuitry within the phone enables the transmitter and receiver to use a single antenna for full-duplex communication.

Antenna The antenna for a cellular telephone can consist of a flexible rubber antenna mounted on a hand-held phone, an extendible antenna on a pocket phone, or the familiar curly stub seen attached to the rear window of many automobiles. Antennas and the cables used to connect them to radio transmitters must have electrical performance characteristics that are matched to the transmitting circuitry, frequency, and power levels. Use of antennas and cables that are not optimized for use by these phones can result in poor performance. Improper cable, damaged cable, or faulty connections can render the cell phone inoperative.

Power Sources Cell phones are powered by a rechargeable battery. Nickel-cadmium (NiCd) batteries are the oldest and cheapest power source available for cellular phones. Newer nickel–metal hydride (NiMH) batteries provide extend talk time compared to lower-cost conventional NiCd units. They provide the same voltage as NiCd batteries but offer at least 30 percent more talk time than NiCd batteries and take approximately 20 percent longer to charge.

Lithium ion batteries offer increased power capacity and are lighter in weight than similar-size NiCd and NiMH batteries. These batteries are optimized for the particular model of cellular phone, which helps ensure maximum charging capability and long life.

Newer cellular phones may operate with optional highenergy AA alkaline batteries that can provide up to 3 hours of talk time or 30 hours of standby time. These batteries take advantage of lithium–iron disulfide technology, which results in 34 percent lighter weight than standard AA 1.5- volt batteries (15 versus 23 grams per battery) and 10-year storage life—double that of standard AA alkaline batteries. Vehicle-mounted cell phones can be optionally powered via the vehicle’s 12-volt dc battery by using a battery eliminator that plugs into the dashboard’s cigarette lighter. This saves useful battery life by drawing power from the vehicle’s battery and comes in handy when the phone’s battery has run down. Abattery eliminator will not recharge the phone’s battery, however. Recharging the battery can only be done with a special charger.

Lead-acid batteries are used to power transportable cellular phones when the user wishes to operate the phone away from a vehicle. The phone and battery are usually carried in a vinyl pouch.