A Brief Introduction to RDS
(Radio Data System for FM broadcasting)
The use of more and more frequencies
for radio programs in the VHF/FM range make it
increasingly
difficult to tune a conventional radio to a desired
program. This
kind of difficulty is solved with the Radio Data System, that has
been on the market since 1987, and whose spectacular evolution is
still continuing. RDS has by now conquered all receiver price
classes and one can easily imagine that it will soon be part of the
standard equipment of any radio receiver.
The development of RDS started some
20 years ago in the European Broadcasting Union, EBU. The developers
aimed at making radio receivers very user-friendly, especially car
radios when these are used where a transmitter network with a number
of alternative frequencies (AF) are present. In addition listeners
should be enabled to see the program service name (PS) on an eight
character alpha-numerical display and the transmitter frequency
information, displayed on non-RDS radios, is then only used, in the
background, by an RDS radio. All this has become possible by the
using, for many years, microprocessor controlled PLL tuner
technology,
permitting
a radio to be retuned within milliseconds.
During this process the audio signal is muted which because of the
short time is usually not detected by the ear. Thus, the radio is
able to choose the transmitter frequency, among a number of
alternatives, that gives the best quality reception. It is also sure
that the switch-over is made to exactly the same program service
by performing a kind of identity check using the program identity
(PI) code.
Travel information with RDS is
possible using the Travel Program (TP) and Travel Announcement
(TA) flags. Information is broadcast for motorists, identified in
parallel with the ARI system with the corresponding RDS features TP/TA.
But ARI is being replaced on a European scale, so it will cease
after the year 2005. A more recent development of RDS is the
digitally coded Traffic Message Channel (TMC) which is now planned
to be introduced all over Europe, within projects funded by the
European Union. However, present RDS radios are not yet suitable for
RDS-TMC.
Once a radio is tuned to a program
service broadcast within a network, using the RDS feature Enhanced
Other Networks (EON) additional data about other programs from the
same broadcaster will be received. This enables the listener,
according to his choice, to have his radio operating in an automatic
switch-mode for travel information or a preferred Program Type
(PTY, e.g. News) and this information comes from a service that, at
a given time, does not necessarily contain such travel information
nor even broadcasts the desired program
type.
Many of the Hi-Fi home tuners or
receivers at this IFA implement, apart from the usual RDS features
(PI, PS, TP,TA, AF), some of the newer features such as Program
Type-PTY, Radiotext-RT and Clock-Time, displaying the time/date.
RDS is absolutely future proof and
will not be replaced by DAB, at least until such time as when FM
broadcasting ceases to exist and this, for sure, is not going to
happen within the next 20 years, in spite of the breathtaking
developments of the new era of digital broadcasting.
There are a number of recent developments in
the availability of RDS equipment, both from a receiver and from a
transmitter standpoint, and in the status of the RBDS standard (the document
which governs the use of RDS in the U.S.), which should be of interest to
broadcasters.
At 1997 NAB Radio Show, Inovonics, Inc. of
Santa Cruz, CA, displayed their new Model 701 RDS/RBDS
"Mini-encoder" which, at $390, is the lowest-cost option available
to broadcasters for getting an RDS signal on-the-air. This device comes
packaged in a small box and supports the following RDS message types:
PS
(Program service name e.g. LIVE-105)
PI
(Program identification e.g. station
call sign)
PTY
(Program type; from list of 31
categories)
AF
(Alternate frequency list - up to 7
alternate frequencies of affiliated stations)
RT
(Radiotext - a 32 character message
to scroll across the receiver display)
M/S
(Music/speech switch - indicates
music or speech-only)
DI
(Decoder I.D. - indicates mono or
specific binaural/stereo mode in use)
The Model 701 does not require a dedicated
host computer for operation, however a computer with a parallel port is
required for programming the appropriate messages and other required
information into the unit (using Inovonics-supplied software). Any
broadcaster who has considered using RDS, but elected not to because of the
equipment costs, may want to look at this device. Manufacturers of RDS
encoding equipment include Modulation Sciences, CRL, RE America and others.
Also in 1997 the National Radio Systems
Committee (NRSC) met and voted to send the revised RBDS standard to the full
NRSC membership for approval. This is a revision of the original RBDS
standard which was adopted by the NRSC in 1993 and which was based on the
RDS standard developed by European broadcasters in the late 1980's. The U.S.
standard was named RBDS (Radio Broadcast Data System), as opposed to simply
RDS, to distinguish it from its European counterpart, due to small (but
important) differences between the two standards. (While the two standards
themselves have different names, the same equipment is typically used with
either and is commonly referred to simply as "RDS" equipment.)
Both the NRSC and the European standards have
recently been revised to reflect the experience gained by the use of RDS,
and to make RDS a more flexible and useful data delivery system.
As a result of this revision process, the
NRSC and the CENELEC versions of the standard have been harmonized to more
closely approach a single, worldwide RDS standard. This should simplify the
manufacture of RDS-capable receivers for worldwide use.
One of the major concerns of U.S.
broadcasters regarding the deployment of RDS has been the slow pace with
which receiver manufacturers have embraced this technology. Recent
announcements by car manufacturers may signal that this trend is finally
changing.
Most significantly, Cadillac is the first
U.S. car manufacturer to offer an RDS radio as standard equipment in the
1998 Seville STS model. This car was recently shown to journalists at a
press briefing in the Washington, DC area where its many features were
demonstrated. One advanced feature of the radio is a diagnostic mode, only
accessible by a "secret" sequence entered using the radio's front
panel controls, which displays the relative signal strength of the FM
carrier, and the block error rate of the RDS signal on that carrier, in
real-time.
This radio, while on the "high end"
of the economic scale and perhaps out of reach of the "mass
market," signals a trend which is very likely to reach into the more
affordable product lines of U.S. automakers in the next few years. Shown in
the table is information on the current availability of RDS radios as
standard equipment in automobiles (source: TWICE magazine, 8/18/97).
