Specifications

Rockwell Automation Publication AG-SG001G-EN-P - April 2015 47
Choosing Data Communication Equipment Chapter 3
• Required standards (for example, UL, CSA, or FCC)
• Whether the radio modem is composed of an integrated unit or a radio
and a modem as separate units
• Radio modem design and operation
• Data security
• Required response time
• Ability to buffer serial data and avoid data collisions between radio
modems to allow Report-by-Exception
• Ability to route DF1 data packets and to store and forward
Licensing
There are two major types of radio networks; licensed narrow-band fixed-
frequency radio and unlicensed spread-spectrum radio.
Licensed Fixed-frequency Radio
Licensed narrow-band fixed-frequency radio operate in the UHF/VHF bands.
The FCC requires that you obtain a license before you operate a radio modem at
a particular location and frequency within these radio frequency bands.
Unlicensed Spread-spectrum Radio
Alternatively, the FCC allows you to use relatively low transmit power, spread-
spectrum radio modems without a license.
Spread-spectrum radio systems operate in the 900MHz and the 2.4/4.8
industrial, scientific, and medical (ISM) bands.
There are two implementations of spread-spectrum currently in use:
Direct-sequence spread-spectrum (DSSS) radio takes the same data that
would be transmitted on a single narrowband fixed frequency and
transmits it over an available wideband of frequencies at a reduced power
level.
Frequency-hopping spread-spectrum (FHSS) radio also takes the same
data that would be transmitted on a single narrowband fixed frequency,
but in this case transmits it over a sequence of narrowband frequencies over
the available wideband. That is, it 'hops' from one narrowband frequency
to the next.