Specifications

Rockwell Automation Publication AG-SG001G-EN-P - April 2015 53
Choosing Data Communication Equipment Chapter 3
• Ethernet supports higher transmission speeds. However, consider that this
may be offset by the fact that Ethernet is usually less efficient in
transmitting industrial data than serial protocols. This is because industrial
data typically consists of smaller packets (for example, control
information) than commercial data (for example, file downloads). The
overhead of an Ethernet packet is usually much greater than that of a
typical serial packet.
• Ethernet radio modems typically operate in higher, spread-spectrum/
unlicensed frequency bands (900Mhz, 2.4/5.8 GHz) that are limited in
allowable output power and thus have less range than traditional licensed
fixed frequency serial radio modems.
Radio Modem Installation Guidelines
For a radio system, you need these components.
When becoming involved with radio system design, consult radio system
vendors. A site survey should always be performed to determine the following:
• Radio transmit power requirements
• Quantity of radios
• Whether or not repeaters are needed
• Antenna type and heights
Choosing a Satellite
Transmission System
A Very Small Aperture Terminal (VSAT) network provides a mechanism for
multiple remote sites to communicate with a central site (a hub) on a shared
access basis. You can choose between single-hop and double-hop systems.
Single-Hop
Data is transmitted across leased lines to the master Earth station, which beams
the data to the satellite. The satellite beams the data to the remote sites (or master
site).
The charges may be high if you purchase your own inbound and outbound
channels, and usually, you do not use the channels' entire bandwidth. Also, you
must pay for the leased line that transports the data to the master hub.
Component Comments
Antennas The height and quality depend upon the application and project budget.
Cabinets Consider the environmental conditions or the location of the remote sites
to select an appropriate cabinet.
Repeaters
(optional)
If the radios are not located in a line of sight with each other (for example,
due to terrain), you may need repeaters to carry the signal from the
initiating station to the destination station.
Earth