RDS RX

Decodes RDS (Radio Data System) data carried alongside the audio of FM broadcast stations and shows the station's identity and text in real time.

This is an external app (.ppma file on the SD card).

Overview

RDS is the digital data stream that FM stations broadcast on a subcarrier next to their audio. It carries the station identity, programme type, a traffic flag and scrolling text. The app FM-demodulates the selected station, recovers the RDS subcarrier at 57 kHz, decodes the biphase-coded groups and displays the fields below.

Tune the frequency field to an FM broadcast station (87.5–108 MHz). A strong, clean FM signal is needed for stable decoding.

Controls

Control	Description
Frequency	Tune to an FM station (100 kHz steps).
RF Amp	RF amplifier: 0 = off, 1 = on (+14 dB).
LNA	IF gain (0–40 dB). See Receive Quality Issues.
VGA	Baseband gain (0–62 dB).
RSSI / Channel	Signal strength and channel power meters.

Decoded fields

Field	Meaning
PI	Programme Identification code (hex) — uniquely identifies the station / network
TP	Traffic Programme flag (Yes / No) — station carries traffic announcements
PTY	Programme Type as number + name (e.g. News, Pop, Rock, Classics, Weather, Sport)
PS	Programme Service name — the 8-character station name, built up from type 0A/0B groups
Radio Text	Free-text message from the station (up to 64 characters, type 2A/2B groups), shown on three lines

Below the fields a diagnostic console prints each received group as its four raw blocks [A B C D] followed by the group type (e.g. G:0A, G:2A). Blocks that failed the error check are shown as ----.

Protocol

RDS is transmitted on a 57 kHz subcarrier (the third harmonic of the 19 kHz FM stereo pilot), biphase-coded at 1187.5 bit/s and arranged in groups of four blocks, each protected by an error-correcting checkword.

See also

• RDS — transmit RDS data with the RDS TX app