Chapter Three
Operation
Page 19 November
2008
Increasing
frequency
1
6
11
2
7
3
8
4
9
5
10
LED Indicator
Condition
Meaning
DIO OFF
Digital output OFF
and
input is open circuit
The Ethernet RJ45 port incorporates two indication LEDs. The LINK LED comes on when there is
a connection on the Ethernet port, and will blink off briefly when activity is detected on the
Ethernet port. The 100MB LED indicates that the connection is at 100 MBit/Sec. The 100MB
LED will be off for 10MB/Sec connection.
Other conditions indicating a fault are described in Chapter Six, “
Troubleshooting
.”
3.2
Selecting a Channel
The D2 W MDME 2400 conforms to the IEEE 802.11 Wireless LAN specification. The D2 W
MDME 2400 supports 11 radio channels, each 5 MHz wide, in the range 2412 MHz to 2462 MHz.
Only one of these channels is used for a connection. The desired channel is selected and configured
at the Access Point, and is then used for all beacon transmissions and connections. Clients scan all
11 channels for a suitable Access Point and then adopt the same channel as the AP when a
connection is established. Although each channel is only 5 MHz wide, the radio transmission is
much wider. Hence, the channels
overlap
. The following diagram shows the RF energy
distribution for a Wi-Fi transmission:
Most of the energy is in a central 22 MHz wide “lobe,” centered around the channel frequency;
however, there are also side lobes extending either side.
If we ignore the side lobes and consider each Wi-Fi
message as a 22 MHz wide transmission, then the
following diagram represents how transmissions in
each channel overlap.
If there is more than one Wi-Fi AP within the same
wireless range, then it is important that the APs are
on channels as far apart as possible. If there are only
two APs, set them to 1 and 11. If there are three, set
them to 1, 6, and 11.
It is also important that the correct channel is
selected for the region. Channels 1 to 11 are
approved for North America (FCC), Europe (ETSI), Canada (IC), and Australia (ACMA).
Channels 10 and 11 are approved for use in Spain and France. Refer to the relevant regulatory
authority for the region as to which radio channels are approved for use.
f-33
f-22
f-11 f
f+11 f+22
f+33
RF power distribution in a Wi-Fi transmission with channel central frequency, f
