RTcom Radio Modems User Manual

User Manual

RTcom-Universal, Global

Max and Outback

Radio Modems

Copyright Radio-Tech Limited 1998-2000

2

CONTENTS

INTRODCUTION 3

Selecting the frequency of operation 5
R.F Path Surveys 5

INSTALLATION

Power Supplies 6
Location 6
Antenna Feeders 7
Lightning Surge Protection 8
Antenna Installation 9
Antenna Options 10

GENERAL ARANGEMENT

RTcom-Global and Universal 11
RTcom-Outback 12
RTcom-Max 12

CONNECTIONS

Data and Power 13

CONFIGURATION

Operating Modes Table for the RTcom range 14
Data format mode switch 15
Interface mode switch 15
Data rate setting chart 15

OPERATION

Status LED's 16
All LED's Blinking 16

COMMISIONING 17

COMMUNICATION PROTOCOLS

The RTcom protocol 17
Using proprietary protocols 17
Using WindowsTM Terminal or Hyper Terminal 17

EMC Conformity 18

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INTRODUCTION

The RTcom-range of radio modem is intended as a direct replacement for cables over short, medium
and long distance, serial data links. They are suitable for part of point-to-point, master to slave or
scanning telemetry links, where the modem is either used on its own our in conjunction with existing
cables. The modems also operate transparent to many industry standard network protocols, such as
Modbus and Eiba Bus and can be used with many manufacturers PLC communication protocols.

Serial Data Serial Data

RTcom
Modem

Fig 1: Simple point to point link

RTcom
Modem

The advantages of wire free communication offered by Radio Modems such as Radio-Tech Universal,
Global, Europa, Outback and Max are numerous. These include reduced installation cost, the ability to
cross-awkward terrain, cross third parties lands, cross-rivers and operate from moving objects.

RTcom
Modem

Master station

RTcom
Modem

RTcom
Modem

Slave Station (1)

Slave Station (2)

Polled Master to multiple slave system

Thousands or RTcom radio modems are now in service throughout the world, many operating 24hrs a
day, all year round. However, for any radio communications system to be reliable care should be
taken in the design of the whole system. Many countries impose restrictions on the frequency, power,
channel power and occupied bandwidth of transmissions. Others in addition impose strict test and
certification procedures on equipment while others permit a free for all!

4

In many countries it is quite legal to operate systems without need for operating licences. These
countries include the United Kingdom, Australia, New Zealand, Korea, South Africa, Scandinavia and
the majority of Europe. However, operation in these countries is normally subject to the equipment first
being approved to a defined standard, such as the UK MPT1329 or the European ETS 300-220-1.

Other countries, such as the United States also permit unlicensed transmissions under FCC- Part 15,
but both the power and duty cycle limits imposed make modem operation impractical for reliable
operation over distance more than a few tens of meters.

Before using your RTcom Radio Modem please ensure that you have purchased the correct version
and selected the correct frequency of operation. We have versions with many international approvals
ranging from FCC-Part 90 through to Australia Standards and our European versions carry the CE
mark. If in doubt please ask your local Radio-Tech Limited agent.

5

Frequency of operation

Often there is not a choice over operating frequency. In most countries frequency allocations are very
limited, by way of example in Europe there is only 433-435MHz UHF or 868-870MHz SHF. While the
UK and many others offer VHF, UHF and SHF allocations. However other frequencies may be used
subject to local government licence.

In order to generalise the choice of frequency should be based upon the distance of intended
operation, power supply constraints, data rate, duty cycle, attenuation, portability (antenna size) and
the presence of other users. The following table is produced to assist your choice:-

VHF (10mW) UHF (10mW) UHF (500mW) SHF (5mW) SHF

Free Space Transmission
range
Industrial installation
In large buildings
Penetration through
concrete walls
Ability to bend/ defract
around obstructions
Antenna size (dipole) 43cm 17cm 17cm 8cm 8cm
Potential users in adjacent
channels

Transmission efficiency
For battery operation
Relative cost *** ***** ***** ******* ******

5-10km 3-5km 10-30km 100-200m 5 - 10km
50-700m 50-500m 50m-1km 10-30m 30-100m
********** **** ****** * **
********** ****** ****** ** **

Message pagers
Radio Microphones

********** **** **** *** ***

Radio
Amateur on
433MHz

Radio
Amateurs on
433MHz
Message
Pages on
458MHz and
TETRA on
410-430MHz

CT2
Mobile
telephones

(500mW)*
*

CT2
Mobile
Telephone
s

R.F path Surveys

The only certain way of determining the suitability of a communication channel is to conduct a radio
path survey and spectrum scan.

The spectrum scan is something normally conducted prior to ordering a system. Normally this requires
the use of a good quality scanning receiver such as an ICOM 8500 and a broadband antenna. Failure
to use a quality scanner may result in signals being missed if channel resolution is too low and false
signals being detected if co-channel and image rejection is poor.

When scanning, both the desired and adjacent channels should be checked for signals. As
transmissions may be intermittent it is important to take time with the scan, stopping for as long as
possible on each channel and looking for at least 15-minutes on the final chosen band.

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If there is doubt over the signal reaching the receiver a path survey should be conducted. The outback
modem includes a test mode that places the modems transmitter into constant transmit mode. This
permits the measurement of signal strength at the receiver. Normally our modems will work
satisfactorily with a signal level below 1uV (-107dBm).

INSTALLATION

Power Supplies:

As with any radio communications system, the RTcom modem should be connected to a clean and
stable supply. Switch mode power supplies are rich in RF harmonics and should not be used. Please
note that in many cases as CE sticker on a power supply is insufficient protection against potentially
damaging harmonics. The reality is that the EMC pass limits are set at only -57dBm (316uV), whereas
a radio is quite capable of operation down to an beyond -115 dBm (0.5uV). Hence, a power supply is
capable of legally generating harmonics quite capable of blocking the modems operating channel. As
a word of warning the frequency of the offending harmonics can shift with both ambient temperature,
time and power supply load. Please do not be fooled into thinking that a system fine only to find that
later it fails due to blocking from its own power supply. Hence as a rule of thumb we only recommend
the use of linear power supplies. Similarly where supply interruption is to be protected against, we
recommend the use of float charged (12V or 24V dc) batteries and not switching UPS's.

Location:

For indoor installations we recommend that the modem is located away from sources of heat and
electrical apparatus such as inverters. Care has to be taken to minimise cable lengths both with
respect to the antenna location and the attached terminal equipment. Generally RS232 should be
used for short distance links < 30ft (10m) and RS422 / RS485 for long links of up to 1000ft (300m). In
practice the maximum distance achievable will depend upon the combination of the drive capability of
both the modem and data terminal.

The IP65 rating of the modem enclosure would to many imply that it could be operated outdoors in all
weather conditions. Experience has shown this to be true, but operation can be jeopardised through
long term exposure to rain, frost, direct sunlight, chemicals and blown sand. For these reasons we
also recommend that where possible the modem should be mounted within a second enclosure of a
similar IP rating and where the climate is variable a thermostatically controlled anti-condensation
heater used. This practice has been used by our own field service engineers for many years and has
proven very successful.