FM RDS 简介

听的收音，有主要的两种发射方式，分别是FM和AM，其中又以FM的音质为好，并且是立体声，但它的弱点，就是传输的距离太短，而这恰是AM的优势。RDS结合了两者的优势。

AF功能

根据信号水平，自动在不同频点切换，保证了更好的收听效果和更大的收听范围。

通常一个广播电台想扩大它的覆盖率，肯定会进行多个频率点的发射。

如果你正在收听的电台的信号良好时，它是不做任何事情，当信号低于某个水平的时候，AF功能会自动搜索当前电台的其他的发射频率（这个过程你是不知道的，而且是绝不会误串到别的电台上去），当AF找到另一个信号比原来的好、稳定的频率时，就会自动跳转过去（当然，节目还是一样的) 。

TA功能

RDS可以将电台名称、节目类型、节目内容发射到收音机上来显示，其实RDS收音机还可以自动将电台的节目类型进行分门归类的。一般的汽车音响的RDS收音机，可以存储30个左右的节目类别：像是什么新闻、体育、娱乐等等。

当你正在收听节目已经收不到信号了，它会自动去搜寻你爱听的同类型节目的电台，并且是信号最好的一个才被选出来。

“交通信息”功能

RDS电台为了保证汽车的行程安全，独有一个“交通信息”功能。就是万一有什么重大的交通信息，比如公路塞车啊，车祸啊，塌方啊，电台就会发送特殊的交通信息，这是你的RDS收音机就会亮起“TP”灯，无论你的音响是在听歌还是在放DVD或着打游戏，它都会强行中止一切动作，然后插入播放交通信息。

具有RDS功能的电台：87.8（深圳）、88.1（雷霆台）、90.7（商台）、93.2（香港一台）、97.3（好象是香港四台）

--------下面摘自Wiki-------

Radio Data System, or RDS, is a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts. RDS standardises several types of information transmitted, including time, station identification and programme information.

Radio Broadcast Data System (RBDS) is the official name used for the U.S. version of RDS. The two standards are only slightly different.

The standard began as a project of the European Broadcasting Union (EBU), but has since become an international standard of the International Electrotechnical Commission (IEC).

Content and implementation

The following information fields are normally contained in the RDS data:

AF ( alternative frequencies)

This allows a receiver to re-tune to a different  frequency providing the same  station when the first signal becomes too weak (e.g., when moving out of range). This is often utilized in car stereo systems.

CT (clock time)

Can synchronize a  clock in the receiver or the main clock in a car. Due to transmission vagaries, CT can only be accurate to within 100 ms of  UTC.

EON (enhanced other networks)

Allows the receiver to monitor other networks or stations for  traffic  programmes, and automatically temporarily tune into that station.

PI (programme identification)

This is the unique code that identifies the station. Every station receives a specific code with a country prefix. In the US, PI is determined by applying a formula to the station's  call sign.

PS (programme service)

This is simply an eight-character static display that represents the call letters or station identity name. Most RDS capable receivers display this information and, if the station is stored in the receiver's presets, will cache this information with the frequency and other details associated with that preset.

PTY (programme type)

This coding of up to 31 pre-defined programme types (e.g., in Europe: PTY1 News, PTY6 Drama, PTY11 Rock music) allows users to find similar programming by genre. PTY31 seems to be reserved for emergency announcements in the event of natural disasters or other major calamities.

REG (regional)

This is mainly used in countries where national broadcasters run "region-specific" programming such as regional opt-outs on some of their transmitters. This functionality allows the user to "lock-down" the set to their current region or let the radio tune into other region-specific programming as they move into the other region.

RT (radio text)

This function allows a radio station to transmit a 64-character free-form textual information that can be either static e.g. station slogans or in sync with the programming such as the title and artist of the currently playing song.

TA, TP ( traffic announcement, traffic programme)

The receiver can often be set to pay special attention to this flag and, for example, stop the tape/pause the CD or retune to receive a traffic bulletin. The TP flag is used to allow the user to find only those stations that regularly broadcast traffic bulletins whereas the TA flag is used to stop the tape or raise the volume during a traffic bulletin.

TMC ( Traffic Message Channel)

Digitally encoded traffic information. Not all RDS equipment supports this. Often available for  Automotive navigation systems. In many countries only encrypted data is broadcast, and so a subscription and appropriate decoder is required to use.

RDS support

As far as implementation is concerned, most car stereos will support at least AF, EON, REG, PS and TA/TP.

• More expensive car stereos will offer TMC, RT and / or PTY, perhaps with "NEWS" override.
• Home systems, especially hi-fi receivers, will mainly support functions like PS, RT and PTY.

Program types

The following table lists the RDS and RBDS Program Type (PTY) codes and their meanings:

PTY code	RDS Program type (EU)	RBDS Program type (North America)
0	No programme type or undefined	No program type or undefined
1	News	News
2	Current affairs	Information
3	Information	Sports
4	Sport	Talk
5	Education	Rock
6	Drama	Classic rock
7	Culture	Adult hits
8	Science	Soft rock
9	Varied	Top 40
10	Pop music	Country
11	Rock music	Oldies
12	Easy listening	Soft
13	Light classical	Nostalgia
14	Serious classical	Jazz
15	Other music	Classical
16	Weather	Rhythm and blues
17	Finance	Soft rhythm and blues
18	Children’s programmes	Language
19	Social affairs	Religious music
20	Religion	Religious talk
21	Phone-in	Personality
22	Travel	Public
23	Leisure	College
24	Jazz music	Unassigned
25	Country music	Unassigned
26	National music	Unassigned
27	Oldies music	Unassigned
28	Folk music	Unassigned
29	Documentary	Weather
30	Alarm test	Emergency test
31	Alarm	Emergency

The later RBDS standard made no attempt to match the original RDS plan, therefore several identical radio formats were given different numbers, including jazz, weather, sports, and rock. Other similar formats such as varied/college and phone-in/talk are also mismatched. This is mainly a problem for portable radios taken overseas.

Scrolling Program Service messages are illegal in the U.K.^{[citation needed]} and expressly forbidden by the RDS standards for all countries because of the potential of distracting drivers on the road and causing problems with receiver memory stores. Scrolling messages are, however, widely used in mainland Europe and are common in the U.S.