e991042.pdf

GENERAL INTEREST

RadioText

Radio Teletext

now also in Europe

Some European broadcasting organizations

have introduced, or are introducing, an

improved version of the Radio Teletext service

inaugurated in the United Kingdom by a num-

ber of commercial radio stations in the late

1980s. Like the UK Radio teletext service,

RadioText is separate from, but in addition to,

RDS (Radio Data Services). The RadioText data

are carried on a 76 kHz sub-carrier (UK Radio

teletext: 69 kHz), FM (FSK) modulated at

16 Kbit/s (UK: 5 Kbit/s) with the FM carrier devi-

ated by ±5.5 kHz (UK: ±7.5 kHz). Sony has

designed a receiver, Textman, specially for the

reception of the RadioText service.

INTRODUCTION

The Radio Data System (RDS) is a

European system for broadcasting dig-

ital data on VHF/FM transmitters. The

spectrum of the VHF/FM signal is

shown in Figure 1 . Receivers equip-ped

with RDS decoders decode the digital

data which may include automatic tun-

ing, station identification, service iden-

tification, accurate time, a radio paging

service, and much other information,.

The RDS specification was adopted

by the European Broadcasting Union

(EBU) in 1984 and is now implemented

on most European VHF/FM broadcast

transmitters.

Information at a data rate of

1.1875 Kbit/s in groups of 104 bits is

superimposed on to a 57 kHz sub-car-

rier locked to the 19 kHz stereo pilot

tone. The final multiplex (L+R signal,

19 kHz pilot tone, L–R signal on a sup-

pressed 38 kHz sub-carrier, and the

RDS signal) frequency modulates the

main carrier.

Each of the groups of 104 bits into

which the bit stream is divided is sub-

divided into four blocks of 26 bits. Each

block contains a 16-bit information

word and a 10-bit checkword for,

By our Editorial Staff

Elektor Electronics

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among others, error detection and a

degree of error correction.

Amplitude

Stereo pilot tone

DATA RADIO CHANNEL

In the early 1990s, the American com-

pany Digital DJ introduced a special

data service, called Data Radio Chan-

nel – DARC – for VHF/FM broadcasts.

The system was developed by the

NHK Science & Research Laboratories

in Tokyo. Note that this is not based on

the American Subsidiary Communica-

tions Authorization (SCA) system that

dates from the early 1980s and on

which the UK Radio Teletext service is

based. The system has been accepted

by the International Telecommunica-

tions Union (ITU) as a standard.

It is interesting to note that the

DARC occupies a band of 16 Kbit/s,

which is more than ten times as wide

as the RDS channel (1.1875 Kbit/s).

The DARC is broadcast in the USA

to support normal radio programmes

with Programme Associate Data (PAD).

This service enables programme infor-

mation, such as names of performers,

cast lists, station identification, and so

on, to be displayed on the liquid-crystal

display (LCD) of a suitable receiver or,

by means of appropriate software, on

the monitor of a computer.

L - R

'S' channel

L - R

HSS (high speed subcarrier)

RDS

15 kHz

19 kHz

53 kHz

76 kHz

95 kHz

38 kHz

57 kHz

Frequency

990016 - 11

running Workbench

of Digital DJ. After

encoding, the signal is

sent in accordance

with the USEP emula-

tion protocol to the

main transmitters via

a microwave network

and a DARC encoder—see Figure 3 .

Figure 1. Spectrum of a

VHF/FM signal that con-

tains the normal stereo

audio signals, the RDS

data channel, and the

Data Radio Channel—

DARC.

play. This means that

the waiting times

when leafing through

pages on TV Teletext

are not encountered

with RadioText.

Because of the error

correction, pages can-

not be mutilated: a page is received

either in good order or not at all.

The resolution of the LCD on the

Textman receiver is seven lines each of

not more than 21 alphanumeric char-

acters. Graphics, such as logos, may

also be displayed. All information is, of

course, in black and white.

In Europe, as in the UK and USA,

RadioText is primarily

of interest to commer-

cial broadcasters, since

the service is free (so

far) to the recipient

and must, therefore,

be paid for by adver-

RADIOTEXT

Most data on the RadioText service are

derived from the local television’s tele-

text service but, although this latter ser-

vice contains thousands of pages,

RadioText will be limited to a few hun-

dred. These pages will be transmitted

again and again,

repeated every few

minutes. The Textman

or other suitable

receiver stores all the

information before it

can be seen on the dis-

DARC TECHNOLOGY .

In the DARC, data are carried on a

high-speed sub-carrier of 76 kHz—see

Figure 1.

Information at a data rate of

16 Kbit/s is superimposed on to the

76 kHz sub-carrier which, being the

third harmonic of the 19 kHz stereo

pilot tone, is readily locked to this tone.

The final multiplex,

including the L+R sig-

nal, the 19 kHz pilot

tone, the L–R stereo dif-

ference signal on a sup-

pressed 38 kHz sub-car-

rier, and the DARC sig-

nal, frequency

modulates the main car-

rier at ±5.5 kHz.

The modulation fac-

tor is 0.1. The level of the

high-speed sub-carrier

may be increased to

–20 dB to reduce any

crosstalk from the main

carrier.

After error correc-

tions and other neces-

sary manipulations, the

bandwidth of 16 Kbit/s is

reduced to 8 Kbit/s, via

which about 1000

alphanumeric characters

per second can be trans-

mitted.

The data superim-

posed on to the high-

speed sub-carrier is gen-

erated via a computer

Figure 2. Typical broad-

casting control room

where data can be pre-

pared for dissemination

via the VHF/FM radio

network.

Elektor Electronics

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23 kHz

and car radios.

The Sony receiver looks like the

familar Walkman™ with controls for

five preset transmitter. It has a black

and white display with associated

menu controls. Its internal memory

enables important messages to be

stored for some time.

A drawback of the receiver is that

an earpiece has to be used since the

lead of this forms the antenna without

which, of course, the receiver works

badly or not at all.

The receiver may be used all over

Europe and, with a suitable configura-

tion menu, in North America.

There is an automatic power-off

facility which ensures that the batteries

are not exhaused when the user for-

gets to switch off the receiver.

An FM data control on the front

panel enables the FM data decoder to

be disabled when no data services are

used. If the receiver is used as a stan-

dard portable receiver, the data

decoder is switched off automatically

after twenty minutes.

DARC

Encoder

Transmitter

USEP

DARC

Encoder

Transmitter

USEP

Microwave

network

Workbench

Digital DJ

Uni-directional

DARC

Encoder

Transmitter

990016 - 12

tisers. However, the

Textman is already pro-

vided with facilities that enable ser-

vices to be paid for before they can be

displayed.

The RadioText service may eventu-

ally also be used for radio paging, but

at present there are no definite plans

for this. Nevertheless, each Textman

receiver is already pro-

vided with a unique

code, which can be

accessed via the menus

Figure 3. Diagram of a

broadcasting network

that transmits Radio-

Text data.

of the receiver.

Figure 4. The Type

SRF-DR2000 Textman

receiver from Sony.

TEXTMAN SRF - DR2000

The only receiver currently commer-

cially available for the reception of

RadioText is the Sony Type

SRF-DR2000 Textman. The ICs used in

the receiver are Sony designs, which

are not (yet) available to other OEDs.

When they become,

the RadioText facility

may also be built into

mains-operated tuners

FINALLY

If the RadioText information is dissem-

inated via low-power local transmitter,

the system may be used to give drivers

parking information in car parks, or

draw the attention of customers in a

department store to special offers, and

so. At music festivals, visitors may be

advised via radio of the names of the

performers and, indeed, what is being

performed.

[990016]

Elektor Electronics

1/99

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