Radio Data System (RDS)
Peter L. Mothersole, Norman W. White · 2023
The Radio Data System (RDS) coder is normally situated at the transmitter and the variable data signals are fed to it over a telecom link. In this respect the radio data system acts as a one-way modem. The modulated RDS signal is applied to the MPX processor where it is added to the stereo-sound MPX signal at the appropriate level. When the data signal is demodulated in a receiver it may be inverted, and differential coding is used so that the data is correct irrespective of polarity. It is divided by four to generate a 912 kHz clock for digital generation of the data signal. The input signal for the decoder is taken from the demodulator prior to any de-emphasis filtering and is band-filtered to separate the 57 kHz RDS signal. Commercial receivers use hybrid decoding circuits which contain the 57 kHz band-pass filter, synchronous demodulator, bi-phase symbol generator and differential decoder as a single element.