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S.J. Parascandolo


Radio System

The radio system is vital to the effective running of the system and allows the Therapia Lane Control Room to communicate to a tram driver, to an operative on foot using a hand portable or to an operative driving one of the three road vehicles easily and clearly.

The Tramlink radio system fully complies with MPT1323 and other trunked radio system protocols. However because Tramlink has only three frequencies (one of which is used for controlling the channel selection and base station operation) it is difficult to take full advantage of the system's capabilities. It is possible (but illegal) to listen in on Radio Scanners. Frequencies are reported to be on some Amateur Radio websites.

Base Stations

The radio base stations are housed in enlarged EM4 track side cabinets at Merton Park, Wandle Park, King Henry's Drive and Beckenham Road. The large aerial at each of these sites is a big give away as is the extra 3rd bay of the EM4 case. The aerials at Elmers End and Morden Road are for Railtrack radio systems.

Off Air Repeaters
The radio system also contains Off Air Repeaters or On Frequency Repeaters (OFRs) which are basically amplifiers positioned at the entrance to the tunnels on the system There are two: One at the north end of the Sandilands tunnels which picks up its signal from the Beckenham Road base station and One under the bridge at Wimbledon that picks up its signal from Merton Park.

The OFR basically receives the radio signal from its donor site, amplifies it and sends it down what is known as a leaky feeder aerial (basically a cable with holes in it) that runs the length of the tunnel. The "leaky" radio signal allows the tram or someone with a hand portable to communicate with Control when inside the tunnel.


Tramlink Base Station
Merton Park
© S.J.Parascandolo


In the Control Room

The radio communications with the trams is by the Radio Dispatcher in the Control Room. This is a touch screen computer. Each radio in each cab of each tram has an I.D. reference known to the computer, which then translates it onto the screen to give the tram number and reference i.e.: 2535A or 2535B.

If the controller calls up a particular tram, they would key in say 2535, and (assuming the radios were switched on), both ends would hear the message. Once the driver presses the foot pedal, the channel is opened between the Controller and the end of the tram the driver is at.

The main hardware for the Radio System, along with everything else is situated in the Equipment Room, below the Control Room in the Depot Building.


Radio Dispatcher
Tramlink Control Room

Radio Equipment Rack
Depot Equipment Room

Radio Protocol

Spelling is done using the 'Phonetic Alphabet' along with the acceptable abbreviations and keywords, as well as coded messages of a sensitive nature.

Numerals are said individually, number '0' = Zero.

Call signs are tram numbers, with each radio unit having an ID number for the control system to recognise.

Radios are in each tram cab and are grouped together for a call received from the controller, i.e. "Tramlink Control to 2535". Once the response is received from the driver in A or B cab, then the group call is replaced by the channel opened by the tram radio.

The controller speaks first in every exchange between the controller and the driver, as well as ending the exchange with 'Tramlink Control Out'. Each intermediate exchange ends in 'over'.

The Tram Radios

The radio in each tram cab is a Simoco FM1200 (not FM1000 as in this photo), complete with status LEDs, volume control, on/off button and numeric keypad. When the radio is on it displays the message 'In Service' and the strength of the control signal it is receiving. The unit is mounted in the centre of the drivers desk at the top.

Tram Radio

There are a series of buttons along the bottom of the display: -

Emergency Call
Priority Call and Call acknowledgment
- Scroll down
+ Scroll up
Call Control

In addition, the Left hand foot pedal is used for Radio communication too. If a driver wishes to contact Control under normal circumstances, he either presses the foot pedal or the Green Button to request control to call them back. The Tram Number and the Driver's Name comes up on the Computer with an audible warning. The Controller then touches the correct part of the screen and the driver will hear a ringing tone from the speaker. The driver then has to press the foot pedal to open the channel.

A Green status LED (above the volume control) is lit when a Radio Channel is Open. A Red status LED (also above the volume control) is lit when the Driver is talking. An Amber status LED (also above the volume control) is lit with an audible warning when the signal strength is so low it has lost contact with a base station. These LED's are in a common cluster, green on the left, amber in the centre and red on the right.

Emergency Calls

These are made by pressing the Red button on the radio. This call then takes priority over any other calls waiting to be answered by the controller and can't be accidentally deleted from the display.

When the controller responds, the driver is required to give the following information: -

  • Where the driver is speaking from
  • Location of the emergency
  • Nature of the emergency
  • Whether the OLE needs isolating
  • Any emergency services required

The controller will then carry out the procedures required and then confirm to the driver the actions that have been taken.

Group Calls

These can be made to all radios for announcements and if the controller requests each tram to acknowledge the announcement, then the amber button on the radio is pressed to confirm the message was received and understood.

Status Messages

The controller and driver have the ability to send status messages to each other. This is so that standard messages, such as driver changes can be sent quickly without the Radio Channel being occupied whilst the message was spoken.

The number of status messages is fixed and each message has an identification number. There are 23 available between the driver and control and 5 between control and the driver. Each message is no more than 16 digits long.

When control sends a status message to the driver, an audible tone sounds and the text message appears on the radio. The driver would acknowledge the message then clear it from the radio.

The driver sends a status message by pressing the white status button on the radio, choosing the required message by scrolling up or down using the + and - buttons and then sending the message by either pressing the foot pedal or by pressing the # button on the keypad.

Voice Recorder

All controller to tram radio conversations are recorded and there is also a separate data logger that records all calls - attempted, successful and unsuccessful.

There is a recording channel for each of the three Touch Screen Despatchers so that any call made using a TSD, either by radio or by telephone, will be recorded.

Voice Recorder and Data Logger
Tramlink Control Room

Evacuating the Control Room

The radio system will continue to work if the Control Room is evacuated and it is possible to set up mobile to mobile calls or portable to mobile calls. However this is not a preferred operating mode. It was used when a fire opposite the Depot forced an evacuation in November 2000.

A 'mobile' control unit is set up in the Controllers Cabin at East Croydon with the controllers using a hand portable or mobile unit to talk to all trams. This was demonstrated and approved by the HMRI before opening. Since the trunked radio system allows direct mobile unit to mobile unit calls the radio equipment switch in the depot equipment room will route calls as required. The mobile units have full functionality so it is also possible to initiate group calls. Status or driver initiated calls to control are still automatically logged and recorded in the system back at the depot.

Controllers Cabin
East Croydon
© S.J.Parascandolo

You can also talk directly from tram to tram, but this is rarely used as it would also occupy a radio channel through the control room and drivers are not taught everything the cab radio's are capable of. There are 48 code numbers, one for each tram cab, so if you wanted to call 2539A from 2551B you could key in a 3 digit number (not related to the tram number) and the radio in cab A of 2539 would ring and display the code for 2551B, once the call had ended then the person in 2551B would have to close the channel by pressing * # . This method of communication was used a lot during testing of the signalling system before opening.

It is also possible (or was until the facility was blocked) to make a telephone call from a mobile or hand portable unit because the radio system is tied in with the PABX (Telephone Exchange). However once one frequency is in use only one other is available for traffic and thus allowing mobile units to make phone calls would cause problems. If two units were to make calls that would tie up the whole radio system until the calls ended. Whilst useful in some circumstances, it is open to abuse and has to be used with caution which is why the facility was blocked.

Dolphin Handsets

In addition to the Tramlink Radio System, Tramlink also use Dolphin Telecom's Mobile Network for business. This is a commercial TETRA system - TETRA stands for TErrestrial Trunked RAdio. This enables virtual networks to be set up between Dolphin Handsets. Tramlink uses these for communicating with some staff during incidents, for communications between Revenue Inspectors and for Back Up purposes on the Beckenham Line.

The Beckenham line runs parallel to Railtrack lines over Railtrack owned land between Beckenham Junction and Love Lane (between Harrington Road and Birkbeck). Railtrack wanted a secondary method of communication for Tram Drivers in the unlikely event of an Emergency occurring at the same time as a Tramlink Radio System failure. The Tram driver would still be able to contact Tramlink Control (who keep a Handset in the Control Room) and they have a Direct Line to the Railtrack Signalman who could stop the heavy rail trains if required.

It is an operating requirement for all trams on this section to carry a Dolphin Handset and they are issued each morning to the first driver of each Route 2 tram.

Dolphin Handset
© S.J.Parascandolo

Many thanks to everyone who has helped with the information on this page.

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