Specifications

Rockwell Automation Publication AG-SG001G-EN-P - April 2015 49
Choosing Data Communication Equipment Chapter 3
Radio Modem Types
There are two types of radio modems: Ethernet modems and Serial modems.
Ethernet Radio Modems
Ethernet radio modems have a standard IEEE 802.3 (10Base-T or 100BaseT)
interface that can connect directly to the Ethernet port on the computer or PLC,
or to the Ethernet network via a bridge or router.
Serial Radio Modems
Serial modems may be sold as:
• integrated units.
– Key-up time between the radio and modem is integrated fully. The unit
does not require programmable controller intervention.
– When the modem and transmitter/receiver are separate, compatibility
becomes an issue.
•two separate units.
– a digital data modem that has an RS-232 connector
– a radio transmitter/receiver that has an antenna connector
Often, since the modem is not able to directly control when the radio transmits a
carrier, the data communication device must also have a way to key-up the radio
transmitter just prior to transmitting data to the modem.
Also, consider the time-to-transmit power requirements of the combination,
since the external modem is not able to determine when the radio is at full power.
The modem requires a time delay prior to data transmission.
Like leased-line modems, the cost of radio modems is directly proportional to the
communication rate or communication throughput that they can support.
Select your modem based on the type of application: point-to-point full-duplex,
point-to-multipoint half-duplex, or multipoint-to-multipoint full-duplex.
For Point-to-point Full-duplex Applications
Choose full-duplex radios. This application requires a separate transmitter and
receiver in each radio modem.