Multi-purpose amplitude modulation (AM) broadcasting system using Single Side Band (SSB) technique

Abstract

In the dissertation a new single sideband (SSB) AM broadcasting system is introduced. In this new system both voice programme and textual (or graphical) information can be transmitted and received simultaneously using the newly developed single sideband technique. The voice programme is carried in one sideband and the textual information is pre-modulated with I:SK in another sideband. Data rate 01' the broadcasting textual information is 1200bps. Each channel only occupies 5kHz bandwidth , the two programmes altogether occupy l0kHz bandwidth , the same bandwidth as in the conventional double sideband AM broadcasting system which is used to send only one voice programme. The prototype of the SSB system was built and tested. An innovative demodulation method is also proposed , which is based on the modification of the phase shift single sideband demodulation method. The input single sideband signal is firstly detected by an envelope detector and a narrow band FM demodulator following by an integrator, then their phase are equalised , they are finally mixed to obtain the upper sideband and lower sideband signals. Unlike the conventional method in which a local oscillator for demodulation is necessary, the proposed method does not require oscillator in the demodulation circuit. Synchronous detection must be used in conventional methods. The proposed method greatly reduces the circuit complexity since it is an asynchronous demodulation method. However it requires a higher noise threshold. The proposed method is apparently useful in full-carrier independent sideband system. The demodulator is theoretically analysis and simulated. It is also implemented and measured. Both theoretical and experimental results demonstrate the feasibility and merits of this method