Apparatus for demodulating AM data multiplexed modulated wave signal

An apparatus for demodulating an AM data multiplexed modulated wave signal to derive therefrom a baseband digital signal, the AM data multiplexed modulated wave signal being obtained by amplitude modulating a carrier having a frequency fc with an analog signal by an AM type modulator to multiplex digital modulated signals at frequency positions of (fc+f.alpha.) and (fc-f.alpha.) line symmetrical to the carrier having the frequency fc on the frequency axis, the apparatus comprising:

• a first orthogonal detector for orthogonally detecting the AM data multiplexed modulated wave signal with a signal having a frequency (fc+f.alpha.);
• a second orthogonal detector for orthogonally detecting the AM data multiplexed modulated wave signal with a signal having a frequency (fc-f.alpha.);
• first calculation means for calculating a difference between I components output from said first orthogonal detector and I components output from said second orthogonal detector;
• and
• second calculation means for calculating a sum of Q components output from said first orthogonal detector and Q components output from said second orthogonal detector.

An apparatus for demodulating an AM data multiplexed modulated wave signal to derive therefrom a baseband digital signal, the AM data multiplexed modulated wave signal being obtained by amplitude modulating a carrier having a frequency fc with an analog signal by an AM modulator to multiplex digital modulated signals at frequency positions of (fc+f.alpha.) and (fc-f.alpha.) line symmetrical to the carrier having the frequency fc on the frequency axis, the apparatus comprising:

• A/D converting means for sampling the AM data multiplexed modulated wave signal when a level of the carrier becomes 0 and A/D converting the sampled signal;
• orthogonal detection means for orthogonally detecting an A/D converted and dispersed output signal with two orthogonal carrier signals having a frequency f.alpha.;
• and
• a low-pass filter for removing high frequency components of an orthogonally detected output.

An apparatus for demodulating an AM data multiplexed modulated wave signal to derive therefrom a baseband digital signal, the AM data multiplexed modulated wave signal being obtained by amplitude modulating a carrier having a frequency fc with an analog signal by an AM type modulator to multiplex digital modulated signals at frequency positions of (fc+f.alpha.) and (fc-f.alpha.) line symmetrical to the carrier having the frequency fc on the frequency axis, the apparatus comprising:

• carrier reproduction means for reproducing the carrier from the AM data multiplexed modulated wave signal and shifting the phase of the reproduced carrier by .pi./2;
• multiplying means for multiplying an output from said carrier reproduction means by the AM data multiplexed modulated wave signal;
• orthogonal detection means for orthogonally detecting the multiplication output signal by two orthogonal carrier signals having a frequency f.alpha.;
• and
• a low-pass filter for removing high frequency components of an orthogonally detected output.