User's Manual

Page 16

M Series Data Radio – User Manual

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 M Series radio modems provide an asynchronous V24 compliant

RS232 port for connection to a serial data device.

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).

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.