A modem is a device that allows the computer to transmit data over telephone lines. A radio modem is a device that works as radio frequency transceiver and receives or transmits the serial data. Wireless access points are used to enable such wireless communication. Radio modem type, bus standards, frequency band, radio technique, data transfer rates, operating modes, and performance are the considerable specifications while selecting a radio modem.

Radio Modem Types

There are two types of radio modems available. One is the internal and other is external. Internal radio modems are the cards that are inserted in the computer slots according to the bus standards or interfaces. External modems are the devices (modules) and are attached to the computer ports or interfaces.

Radio Modem Bus Standards

Several interfaces or bus standards are available that support internal and external modems. These include Serial ports (RS232, RS422, & RS485), Universal Serial Bus (USB), ST, PCL slots, RJ45 connector, ISDN (BRI U & BRI S/T interfaces), Type II & Type III cads, Card Bus, MIC, ISA, and PCI bus standards.

Operating Modes Of Radio Modems

A radio modem works in three operating modes. These are repeater mode, point-to-point, and point-to-multipoint modes. Radio modems in point t point mode transmits to only one radio modems at a time. Radio modems in point to multipoint modes transmit to several modems simultaneously. There are six frequency bands available to allow radio modems functionality. These include VHF (very high frequency band), UHF (Ultra high frequency band), 23GHz, 5GHz, 2.4GHz, and 9MHz.

Radio Techniques

Direct sequence spread spectrum and frequency hopping spread spectrum are the two radio techniques that radio modems offer. Direct sequence spread spectrum technique is favorable to reduce localized frequency interference. Frequency hopping technique divides the channel into sub-channels while signals hops between sub-channels. This technique overcomes with the signals hopping among the channels for shorter times.

Radio Modem Performance specifications

Performance specifications are based on four parameters. These include transmission, maximum output power, sensitivity, and number of channels. Transmission can be full duplex or half duplex. In full duplex radio modems receive and transmit simultaneously. Maximum output power is defined as the strength of the signals transmitted and measured in mille watts. The measurement of the weakest signal in the transmission is known as sensitivity. It is sensed by the receiver and measured in dBm. The receivers with the lowest sensitivity are considered to be the best. The number of receiving and transmitting channels of the radio modem defines total numbers of channels. Two common features that may or may not be included in Radio modem specifications are RF connectors and antenna. Some modems contain RF connectors such as BNC, TNC, and N connectors. These connectors allow attaching as or other suitable RF devices.