10
sensing.honeywell.com
Installation and Technical Manual for the
Limitless™ Multi-Protocol Receiver, WMPR Series
ISSUE B
32309669
4 | R.F. INTERFERENCE
CONSIDERATIONS
4.1 | R.F. Interference Considerations
4.1.1 | General
The 802.15.4 specification provides a high resistance to inter-
ference. Within the 2.4 GHz band, there are 16 channels, each
using approximately 2 MHz of bandwidth. The channel used
may be rapidly changed depending on the presence of other
signals sensed in that channel. Thus narrow band interfering
signals may have no effect, while broadband noise sources may
cause loss. The effect of light to moderate interference is not to
make the system fail, but to increase the rate of “lost packets” of
data. These “lost packets” are simply retransmitted as needed,
so the user may not notice any problem. More serious interfer-
ence can cause loss of more data updates, and error messages
reported by the WMPR, as well as shorter battery life.
4.1.2 | WiFi Networks
Most WiFi (WLAN) networks operate in the same 2.4 GHz range
and use wider bands within that range. Also, the faster proto-
cols (802.11N or AC), may utilize multiple channels. Factors af-
fecting R.F. interference would be channel separation, distance
separation, and duty cycle.
•
Channel separation: Studies have shown that a channel
separation of 7 MHz will make interference less likely. WiFi
routers can be set to use different channels as needed, and
auto channel modes can be disabled. If possible, switch-
ing to a 5 GHz-only protocol (using 802.11N or AC), would
eliminate any possibility of 2.4 GHz interference.
•
Distance separation: A physical separation of 10 meters or
more will reduce possibility of interference.
•
Duty Cycle: Generally the duty cycle of WiFi routers is very
low for simple uses as e-mailing, messaging, most web
browsing, and voice protocols. However, a video camera or
multiple users streaming video would cause a significant
increase in bandwidth usage and increase the possibility of
interference, making channel or distance separation more
desirable.
Regarding the WiFi client (laptop, smartphone, tablet), they are
much less of a problem as they generally operate with a much
reduced duty cycle (most data is received by the device), and
may operate with much lower transmit power
4.1.3 | Smart Phone “Apps”
Smart phone “apps” are available to display consumer WiFi
signal strengths or download/upload speeds. These apps
will not display the 802.15.4 signals as the packet format is
different. However, if a suspected interference source causes a
large reduction in consumer WiFi download speed, it is likely it
could also cause interference to the 802.15.4 data used by the
WMPR.
4.1.4 | Bluetooth
®
Devices
Bluetooth
®
interference is less of an issue, due to the very
narrow bandwidth of Bluetooth
®
signals, the low transmit
power, and the rapid “frequency hopping” of the signals. If the
802.15.4 device misses a packet of data due to a Bluetooth
®
burst of data, the re-transmission of the 802.15.4 data will
likely succeed, as the Bluetooth
®
will have hopped to a different
channel by then.
4.1.5 | Wireless Video Camera and Video Links
Wireless video links operating in the 2.4 GHz band can cause
serious interference as they are operating continuously, use a
wide (6 MHz) bandwidth), and may be more powerful. Interfer-
ence from wireless video could cause the “NO RF” indication in
severe cases. As mentioned, frequency and/or distance separa-
tion may be required.
•
Frequency Separation: Many video links have four or more
channels selectable. Changing channels may help. Addi-
tionally, wireless video links are available in the 900 MHz
band, and the 1.2 GHz band. Switching to one of those
would eliminate interference issues with 802.15.4 (and
802.11x).
•
Distance Separation: Separating the video link sensor from
the WMPR would be very desirable. Alternatively, utilizing
directional antennas on the WMPR, and /or on the wireless
video link would help greatly.
4.1.6 | Microwave Ovens
Microwave ovens operate in the 2.4 GHz range, they are power-
ful, and a high-duty cycle. However, they may not be a problem
to a modern 802.15.4 network. The magnetron in a microwave
oven is driven by half-wave rectified AC, so the R.F. output is
actually off for one half of the 60 Hz or 50 Hz power line cycle
(8.33 msec or 10.0 msec). During that part of the cycle, the
packets of 802.15.4 data may succeed. However, close to half
of the packets may require retransmission, so data throughput
could be greatly reduced.
4.1.7 | Cordless Phones/Baby Monitors/
Intercoms
A 2.4 GHz cordless phone in very close proximity to a wireless
sensor could cause lost packets, while the phone is in use, but
is not a very likely cause. If suspected interference, a simple
remedy is to switch to a DECT 6.0 cordless phone operating on
1.9 GHz.
