Testing RDS-Equipped FM radio receivers

The testing of FM radio receivers equipped with radio data system (RDS) requires an FM transmitter or exciter, a small transmitter that is used to drive an RF power amplifier to create a more powerful signal. The transmitter takes the monaural or multiplexed stereo signal with or without RDS and modulates an RF frequency within the FM band. The audio quality of the transmitter must be better than the receiver under test or the measurements will reflect the transmitter's limitations and not the receiver's. The RDS signal must be added to the audio signal after the FM multiplex stage for testing. Audio Precision offers an RDS encoder utility for use with APx Series Audio Analyzers. The utility creates sine wave test signals and multiplexes and combines them with RDS messages. All frequency response measurements taken from an FM receiver show a sharp high-end roll-off just before 19 kHz due to the FM multiplex filter.