Effect of the imperfections of a quadrature shaper of minimum-FSK signals on the noise immunity of a coherent receiver

The noise-immunity reduction of a coherent detector of minimum-FSK signals is assessed quantitatively as a function of the chief imperfections of the quadrature shaper. These imperfections are the difference between the transmission coefficients of the mixers and deviations of the phase shift of the reference oscillations from pi/2. It is concluded that the required balancing precision of the shaper can be achieved through the digital formation of the quadrature components, switching balance modulators being used as the mixers.