Point-To-Point System; Continuously-Keyed Versus Switched-Carrier Operation - GE MDS 4710A Technical Manual

MDS 05-3305A01, Rev. E

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
plex or half-duplex communication link for the transfer of data between
two locations.
HOST
COMPUTER
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: MDS 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.
MDS 4710/9710 Technical Manual
(Figure 3). This system provides a sim-
Invisible place holder
MASTER
RTU
REMOTE
3