ZFR1800 Series Wireless Field Bus System Technical Bulletin70
Wireless Interference
The ZFR1800 Series Wireless Field Bus System is designed to minimize the
potential for wireless interference with other wireless applications. In most
commercial environments, the ZFR1800 Series System does not encounter or
generate wireless interference, even in environments with cell phones and
competing WiFi applications.
ZFR1800 Series Wireless transmissions use different modulation schemes than
WiFi applications and use frequencies between popular WiFi bands, enabling WiFi
and ZFR1800 Series Wireless networks to exist in the same areas.
The system should not interfere with other wireless systems for the following
reasons:
• No common frequencies exist between the cell phone bands and the 2.4 GHz
Industrial, Scientific, and Medical (ISM) band where the wireless system
operates; therefore, interference should not occur with cell phone
transmissions.
• The 802.11 WiFi standard and the 802.15.4 standard used by the wireless
Metasys systems both use Direct Sequence Spread Spectrum (DSSS) wireless
technology and are specified and required by the Federal Communications
Commission (FCC) to be simple noise sources to each other. These standards
are major advantages for DSSS technology, as each system’s transmissions
typically result in only a slight increase in background noise. The message is
spread across multiple frequencies and the noise allows reconstruction of the
entire message where the noise is virtually undetectable.
• The ZFR1800 Series Wireless Field Bus System operates on the same
frequency band as IEEE 802.11 WiFi networks, but uses different channels.
The ZFR1800 Series System automatically selects non-overlapping, quiet
channels (for example, 15, 20, and 25). See Figure 23.
• The ZFR1800 Series Wireless Field Bus System uses clear channel assessment
to listen to the channel before transmitting on it. This detail means that before
transmitting wireless data on the channel, the device first listens to determine
whether any another device is already transmitting on the channel. Various
wireless technologies also use clear channel assessment, which further helps to
minimize the potential for interference.
• ZFR1800 Series Wireless Field Bus System devices transmit at a low
transmission power of 10 mW. 802.11 WiFi devices typically transmit at 40 to
100 mW. As a result, when both a 802.11 WiFi device and a ZFR1800 Series
System device transmit simultaneously, the ZFR1800 Series System device
only appears as low-level noise to the WiFi device.
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