User guide
Release9.5ReleaseNotes
Issue2,October2009 Page52
8 Collocation
8.1 COLLOCATING5.2‐GHzAND5.4‐GHzMODULES
5.4-GHz radios that are set to a center channel frequency of 5595 MHz or lower produce a signal
that is 280 MHz below their center channel. This signal can interfere with 5.2-GHz channels as
shown In Table 12. Because of this, care needs to be taken in choosing 5.4-GHz channels where
5.4 GHz systems are collocated with 5.2-GHz systems.
Choosing 5.4-GHz channels of 5495 through 5540 MHz or 5600 through 5705 MHz avoids this
collocation issue and is often the best option. Alternatively, provide 100 ft (30 m) of vertical
separation between the 5.2-GHz and the 5.4-GHz radios, or in cases of partial clusters of
5.2-GHz radios, select 5.4-GHz channels that will not interfere.
Table 12: 5.4- and 5.2-GHz interfering frequencies
This 5.4-GHz center
channel (in MHz)…
may interfere with these 5.2-GHz
channels (in MHz)
5545 5275
5550 5275, 5280
5555 5275, 5280, 5285
5560 5275, 5280, 5285, 5290
5565 5275, 5280, 5285, 5290, 5295
5570 5280, 5285, 5290, 5295, 5300
5575 5285, 5290, 5295, 5300, 5305
5580 5290, 5295, 5300, 5305, 5310
5585 5295, 5300, 5305, 5310, 5315
5590 5300, 5305, 5310, 5315, 5320
5595 5305, 5310, 5315, 5320, 5325
Background
What causes this collocation issue? As part of their radio operation, Canopy radios produce a low
level signal outside of their frequency band. By design, this signal is above the band for some
center channel frequencies and below the band for other center channel frequencies. This signal
is present at all times (both during transmit and receive), and is well within regulatory
requirements for out-of-band emissions. However, it is strong enough to interfere with a closely
collocated Canopy radio in another band, if that radio is using a channel impinged upon by the
out of band signal, as can happen between 5.4- and 5.2-GHz radios.
If a CMM provides sync and ensures compatible receive start times (as advised in Collocating
Same-Frequency Band Modules on Page 53), aren’t collocation issues avoided? No. Using sync
and ensuring compatible receive start times are necessary to avoid other collocation issues, but
do not help this collocation issue, because the interfering signal is present at all times, during
transmit and receive.