ESTABLISHING AN RDS NETWORK FOR NATIONAL
PUBLIC RADIO
by Scott Wright, Delco
Electronics
((Editor's note: In August
1997, General Motors Cadillac Division announced that it would be
the first domestic auto maker to offer RDS-capable radios,
starting with its 1998 models. Other auto manufacturers have
followed suit. As the Cadillac Press Release
states, only 10% of the U.S. stations are using RDS, but that
number is expected to increase as more RDS-capable receivers
enter the market. Scott Wright has presented this proposal to EUonline
as a suggestion to coordinate the RDS PI bits throughout the
member stations. We offer this proposal for your consideration.
After examining this proposal, please take a moment to
tell us what you think.))
NPR is a affiliation of subscriber
stations which share programming resources through a satellite
delivery service. NPR differs from a European network in the fact
that NPR stations are individually owned and operated. NPR
stations do not necessarily simulcast the same audio program. In
fact a wide diversity of satellite programming, local
programming, and tape delays make NPR more of a loose affiliation
of member stations rather than a network in the European sense of
the word. Yet NPR is NPR with a loyal group of listeners who can
benefit from the ability of automatically finding a NPR station
wherever they may go. With little coordination and minimal
investment, NPR and its listeners can benefit from RDS, as many
NPR members are already doing so.
RDS FEATURES AT A
GLANCE
| PROGRAM SERVICE (PS)
NAME |
Up to eight alphanumeric
characters at your choosing can be selected as the name
of your station(s). Often times call letters such as
KNPR-FM are used, but slogans are also acceptable. RDS
receivers display the PS instead of the frequency when
tuned to an RDS station.
|
| PROGRAM TYPE (PTY) CODE |
This can be set to any of the
defined types such as "News",
"Sports", and "Classical". There is
even a PTY code defined as "Public" that NPR
stations can use. RDS receivers can seek stations based
on the program type. Hence a user could seek Public to
find a NPR station. Future RDS receivers will allow the
user to interrupt his playback device when a user
selected program, such as "News", becomes
available. Therefore, PTY codes should be thought of as
dynamic rather than fixed in nature. If all NPR stations broadcast
the PTY code "Public", then listeners would be
able to seek automatically to NPR stations. This
certainly is an option for loosely affiliating NPR
stations, but members have expressed a dislike with
having to constantly broadcast "Public" even
when they are broadcasting jazz, classical or news
programs. This also does not take advantage of the
dynamics of the PTY code as is intended. But there is
nothing wrong with broadcasting Public at all times.
|
| PROGRAM TYPE NAME (PTYN) |
Up to eight Up to eight
alphanumeric characters at your choosing can be selected
to further describe your current program type. For
instance, if you are currently transmitting
"Classical" as your PTY, you might define a
PTYN of "Chamber" during an hour of chamber
music. Receivers cannot seek by PTYN, but will display
the transmitted PTYN once tuned to the station.
Broadcasters could transmit the "Public" PTY at
all times, and then vary the PTYN dependent upon the
program material. But again, the listener won’t
automatically find you as they seek for
"Classical" for instance, even though your
program may in fact be classical.
|
| TRAFFIC PROGRAM (TA)/
TRAFFIC ANNOUNCEMENT (TA) |
Stations who give traffic
reports as a part of regular programming inform their
listeners silently through RDS. The listener can then
select whether or not they want to receive traffic
announcements. A traffic announcement will stop the
listeners playback or turn up the volume whenever an
announcement is broadcast. If the traffic is sponsored,
then a brief announcement of that sponsorship prior to
the report could be used as a way of generating revenue.
RDS receivers have a built in search feature to locate
stations that carry traffic programs.
|
| ALTERNATE FREQUENCY (AF)
SELECTION |
This is the core feature that
allows a listener’s RDS receiver to automatically
retune to the best possible frequency. This gives the
illusion to the listener that he is tuned to one rather
powerful station rather than a primary station with
several translators. This is the feature which NPR and
its listeners can greatly benefit from. The Program
Identification (PI) code is a four digit hexidecimal
(0000-FFFF) number that represents the broadcast program.
|
| |
HOW
ALTERNATE FREQUENCY SWITCHING WORKS
AF switching will only occur when the
following thing happen:
1. All the stations
within the "network" share the same PI code.
The PI code is derived from the stations call letters,
therefore the same call letters will need to be used on
all the RDS encoders within the regional network.(ed
note: there are exceptions to this) If STL’s
capable of passing 57kHz audio are used, then only one
RDS encoder is required per regional network, thus
minimizing the cost.
2. The AF list
contains the frequencies of all the stations in the
network.
3. The AF’s have
overlapping coverage areas. This should be based on
actual measured receiving conditions rather than
calculated values. Coverage areas should overlap at an
average of 40 dBµV minimum.
4. The listener
selects AF
switching ON on his RDS receiver.
Then, as the listener drives and the
signal level or other propagation effects such as wide
band AM or ultra sonic noise increase, the receiver will
check the frequencies of the AF list, and attempt to
switch to the best station. The PI code of the AF is
always verified to be a match before the station is
accepted. Figure 1 (below) shows an
example of an RDS network consisting of one member
station and 7 affiliates.
|
| |
The above
scenario works nicely, but only if all stations carry
identical programming. AF networks should not be set up
where the audio content of the AF’s does not match.
Of course this is exactly the case for neighboring,
non-simulcast, NPR stations. NPR
can be defined as a group of mini-networks which make up
a much larger network. AF switching within the
mini-networks is allowable, but other mini-networks can
be automatically tuned when the user recalls a radio
preset. It so happens, that this scenario referred to as
regionalization is provided for within RDS. By making use
of the nationally assigned PI code for NPR (B_01) all NPR
stations can be generically linked providing the
following benefits:
1. AF switching to the
best station for the currently tuned network.
2. Instant tuning to
the best station for all referenced NPR stations when the
listener recalls a radio preset (set to NPR).
3. Automatic search
tuning for any NPR station when the AF memory stores
contain no receivable frequencies.
The following is required to institute
the above network:
1. Each NPR member and
its repeaters/translators (if any) are assigned a PI code
containing the regional variant 4-F indicating local
network programming.
2. Adjoining networks
are assigned a different regional variant. (Overlapping
coverage areas should always use a different regional
variant than all others.)
3. Each network
references all the other networks via Method A or Method
B AF lists for a given geographic area. Method B AF
coding is preferred since the receiver can automatically
detect which stations are variant from the tuned network.
4. Consumer RDS
receivers which:
a.) Recognize
variant PI codes which are mapped to PI codes above
B000.
b.) Have a accept/reject variant
user setting or always reject variants.
c.) Accept variant PI codes on a
preset recall regardless of user setting.
d.) Have a PI search mode which
always accepts variants regardless of user setting.
e.) Should properly recognize
variant PI codes when properly coded in method B AF
lists.
Figure 2 (below) shows
an example of the above described network. Each
mini-network consisting a member and it’s affiliates
is assigned a PI code with a different regionalization
nibble. AF switching occurs only within each
mini-network. The receiver will always tune to the
strongest network whenever the listener recalls the
preset. Single transmitter stations also are referenced.
A central coordinator would handle all PI code
assignments and help member stations properly construct
AF lists.
|
One pre-set button on your car radio could
allow the listener to receive NPR programming where ever they
drive. Simulcast networks (such as a main station, its repeaters
and translators) will automatically be tracked as the listener
travels from reception area to another. Non-simulcast
transmitters are tuned by pressing a preset recall--that is, the
listener must manually switch away from the simulcast network to
which he was listening, such as when the edge of the simulcast
reception is reached and the listener still wants to listen to an
"NPR" station. What we're doing is realizing the
concept that NPR is a network composed of many sub-networks.
Figure 3 Automobile
manufacturers supporting RDS
| COMPANY |
RDS
STANDARD EQUIPMENT IN: |
| Audi |
All models |
| BMW |
To introduce in 1999 model
year |
| General Motors |
Cadillac STS, Available as
option in all other Cadillac models |
| Ford |
Lincoln Continental, Town
Car, Mercury Grand Marquis, Mounaineer SUV, Ford Crown
Victoria, Econoline van, Club Wagon, Explorer SUV, and
Ranger pickup (all CD changer controlling cassette
receivers) |
| Jaguar |
All models |
| Mazda |
SE-5 Plus Pickup |
| Porsche |
All models |
| Volvo |
V70, V70 R |
OTHER IDEAS FOR NPR
Since NPR enjoys satellite feed of program
material, RDS data such as radiotext for artist and song title
and PTY codes for current program material could be automated and
fed from a central point. NPR could also earn revenue by selling
data services via RDS such as paging, differential GPS, or any
other data service through use of the transparent data channel.
The opportunities are only limited by your imagination and your
baud rate.
Complete
the EUonline RDS
Survey, and tell us what you think.
Further Reading:
Cadillac Press Release | Cadillac RDS Radio
Features
www.dungeon.com/~start/rds.html
A private site focusing on RDS, products to buy, RDS contacts
around the world.
www.cemacity.org/mall/product/audio/audio.htm Consumer Electronic Manufacturer's Association Site,
includes a list of RDS-capable receivers.
www.rds.org.uk The
European RDS Forum
www.nab.org/scitech/files/standard.htm
National Association or Broadcasters' RDS site.
Scott Wright is a
recognized pioneer in RDS development. As the designer of Delco
Electronics’ first RDS receiver, he has been extremely
active in the development of the RDS standard in the US and in
efforts to educate the broadcast community about its potential.
He has represented Delco at the European Broadcasting
Union’s (EBU) RDS Forum and is currently the Chairman of the
National Radio Systems Committee RBDS Subcommittee, the US
standard-setting body. He is also a member of the Electronics
Industries Association’s (EIA) RDS Forum. Scott's 1997 book Broadcaster's
Guide to RDS is available from Focal Press in Woburn, WA (http://www.bh.com/focalpress). You can reach him at Delco Electronics Corp.,Mail
Stop R-314,1800 E. Lincoln Road, Kokomo, IN. 46904-9005 voice:
(765)451-1057, email:SAWRIGHT@mail.delcoelect.com
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