AC4490 User Guide
Version 4.5
Laird Connectivity Solutions Support Center:
http://ews-support.lairdtech.com
34
Americas: +1-800-492-2320
Europe: +44-1628-858-940
Hong Kong: +852 2923 0610
A
PPENDIX
II:
S
YNC
-
TO
-C
HANNEL
Note: Information furnished by Laird in this specification is believed to be accurate. Devices sold by Laird
are covered by the warranty and patent indemnification provisions appearing in its Terms of Sale
only. Laird makes no warranty, express, statutory, and implied or by description, regarding the
information set forth herein. Laird reserves the right to change specifications at any time and
without notice. Laird products are intended for use in normal commercial applications.
Applications requiring extended temperature range or unusual environmental requirements such as
military, medical life-support or life-sustaining equipment are specifically not recommended
without additional testing for such application.
Note: For a period of one (1) year from the date of purchase, Laird warrants the transceiver against
defects in materials and workmanship. Laird will not honor this warranty (and this warranty will be
automatically void) if there has been any: (1) Tampering, signs of tampering, or opening the
transceiver’s case. (2) Use of AC power adapters and cables other than those originally supplied
with the transceivers. (3) Repair or attempt to repair by anyone other than a Laird authorized
technician. This warranty does not cover and Laird will not be liable for, any damage or failure
caused by misuse, abuse, acts of God, accidents, electrical irregularity, or other causes beyond
Laird control, or claim by other than the original purchaser.
Sync to Channel - What is it and do I need to use it?
Laird uses frequency hopping protocol with a fixed pseudo-random hopping sequence on our transceivers.
This protocol yields superior interference rejection and multipath immunity. The server sends timing beacons
on a regular interval and clients hear these beacons and synchronize their hopping to the server.
Though servers cannot send packets to each other, they can hear the timing beacons sent out by other
servers. Normally, the servers ignore these beacons. However, when Sync to Channel is enabled, and a
specific server is designated as the synchronization master, the other servers will listen for the beacons from
the master server and then synchronize their hop timing to that server.
Why is this important? If two servers (and their clients) are operating in the same area and their frequency
hopping is not synchronized to each other it’s possible that they might try to occupy the same frequency at
the same time. In severe cases, they could interfere on every frequency, causing very slow communications.
To avoid this kind of interference, collocated servers can use Sync to Channel. Sync to Channel synchronizes
frequency hop timing between these servers so that they never occupy the same frequency simultaneously.
To use Sync to Channel, you should select one server (preferably the most centrally located server) to be the
“Hop Master.” This server should be programmed to a numerically low RF Channel Number and should have
Sync-to-Channel disabled. All other servers in the area should have Sync to Channel enabled and have their
Sync-Channel set to the RF Channel Number of the server chosen as the Hop Master. Preferably, if a server is
outside of the range of the Hop Master Server it can have its Sync Channel set to the RF Channel Number of
another server (with a lower RF Channel Number than its own) that is in range of, and synchronized to, the
Hop Master server.
The following rules apply to Sync-to-Channel:
1.
One server should perform the function of Hop Master.
2.
The Hop Master server should have its RF Channel Number set to a numerically low value and should
have Sync to Channel disabled.
3.
It is preferable that the Hop Master Server be centrally located.
