Radio receiver for frequency-shifted data transmissions - has visual indicators to show that receiver is on-tune, and is receiving both data frequencies

摘要

When digital data are transmitted by radio, the two states '0' and '1' are transmitted as different audio frequency tones which modulate a carrier. The receiver has an indicator circuit which shows that the tuner is set to the correct carrier and is receiving the two frequencies and discriminating between them. The signal from the aerial (1) is fed to a tuner (2). The tuner output is amplified (3), filtered (4) and detected (5), before being fed to a tone decoder (6). The decoder output is fed via a delay circuit (7) to the indicator circuit (8) which has l.e.d.s which light to show the presence of the different tones. The delay output is also fed via filters (9,10) to the data processing equipment.