User's Manual

Page 17
E Series Data Radio – User Manual
© Copyright 2005 Trio DataCom Pty. Ltd.
Part D – System Planning and Design
Common Cable Types Loss per meter Loss per 10m
@ 450MHz @ 450MHz
RG58C/U 0.4426dB 4.4dB
RG213/U 0.1639dB 1.6dB
FSJ1-50 (¼” superflex) 0.1475dB 1.5dB
LDF4-50 (1/2” heliax) 0.0525dB 0.52dB
LDF5-50 (7/8” heliax) 0.0262dB 0.3dB
Data Connectivity
The V24 Standard
The E Series radio modems provide two asynchronous V24
compliant RS232 ports for connection to serial data devices.
There are two types of RS232 interfaces – DTE and DCE.
DTE stands for data terminal equipment and is generally applied to
any intelligent device that has a need to communicate to another
device via RS232. For example: P.C. Comm ports are always DTE,
as are most PLC and RTU serial ports.
DCE stands for data communication equipment and is generally
applied to a device used for sending data over some medium
(wires, radio, fibre etc), i.e. any MODEM.
The standard interface between a DTE and DCE device (using
the same connector type) is a straight through cable (i.e. each pin
connects to the same numbered corresponding pin at the other
end of the cable).
The “V24” definition originally specified the DB25 connector
standard, but this has been complicated by the emergence of the
DB9 (pseudo) standard for asynch devices, and this connector
standard has different pin assignments.
The wiring standard is “unbalanced”, and provides for three basic
data transfer wires (TXD, RXD, and SG – signal ground).
Hardware Handshaking
Hardware handshake lines are also employed to provide flow
control, however (in the telemetry industry) many devices do not
always support all (or any) flow control lines.
For this reason, the E Series modems can be configured for full
hardware flow control, or no flow control at all (simple 3 wire
interface).
Note: that when connecting devices together with differing
handshake implementations, it is sometimes necessary to
“loop” handshake pins in order to fool the devices handshaking
requirements.
In telemetry applications (particularly where port speeds can
be set to the same rate as the radio systems over-air rate)
then flow control, and therefore handshaking, is usually NOT
required. It follows that any devices that CAN be configured for
“no flow control” should be used in this mode to simplify cabling
requirements.
Handshaking lines can generally be looped as follows:
DTE (terminal) – loop RTS to CTS, and DTR to DSR and DCE.
DCE (modem) - loop DSR to DTR and RTS (note-not required for
E Series modem when set for no handshaking).
RF Feeders and Protection
The antenna is connected to the radio modem by way of an
RF feeder. In choosing the feeder type, one must compromise
between the loss caused by the feeder, and the cost, flexibility, and
bulk of lower loss feeders. To do this, it is often prudent to perform
path analysis first, in order to determine how much “spare” signal
can be allowed to be lost in the feeder. The feeder is also a critical
part of the lightning protection system.
All elevated antennas may be exposed to induced or direct
lightning strikes, and correct grounding of the feeder and mast are
an essential part of this process. Gas discharge lightning arresters
should also be fitted to all sites.
Note: All ETSI installations require the use of a lightning surge
arrestor in order to meet EN6095. See Part A - Preface for lightning
arrestor specifications.