WDS 1710 Series, Техническое руководство

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05-3305A01, Rev. E 3
Point-to-Point System
Where permitted, the transceiver can also be used in a point-to-point
system.
A point-to-point system consists of two radios, one serving as a
master and the other as a remote ( Figure 3 ). This system provides a sim-
plex or half-duplex communication link for the transfer of data between
two locations.
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Figure 3. Typical Point-to-Point Link
Continuously-Keyed versus Switched-Carrier Operation
Continuously-Keyed operation means the master station transmitter is
always keyed and an RF carrier is always present, even when there is no
data to send. The master station is always simultaneously transmitting
and listening. Use different frequencies to transmit and receive. This is
the method used in many MAS systems, as is shown in the typical
system in
Figure 2 . This is network arrangement useful for high-speed
polling applications.
NOTE
1710/2710/4710/9710 remotes do not support full-duplex operation.
Switched-Carrier operation is a half-duplex mode where the master sta-
tion transmitter is keyed to send data and unkeyed to receive. The trans-
ceiver uses different frequencies for transmit and receive. This prevents
different remotes from interfering with each other, making it easier to
implement SCADA protocols. This mode results in slower polling times
than a Continuous-Keyed master due to the keying time for the master
and squelch opening time for the remote.
Additional information:
•
Remotes always operate in switched-carrier mode, but can
receive data from a master that operates in either switched-carrier
or continuously-keyed modes.
•
A single-frequency system cannot utilize a continuously keyed
master.
•
An advantage of a continuously-keyed master is that it provides a
constant signal source to remotes that require a constant Data Car-
rier Detect signal.
REMOTE
MASTER
HOST
COMPUTER
RTU