The Stereo FM signal is transmitted, not as Left and Right, but as Sum and Difference. The Sum signal is the Mono signal that can be received by an old FM set that is not stereo. The difference signal is carried above a 19KHz marker tone that activates the stereo capabilities of the receiver (and lights up that little indicator that says "STEREO"). The difference signal goes 20KHz to 40KHz, but is processed down to represent the usual audio range. Then the sum and the difference signals are mixed, so as to get Left and Right. Unfortunately, the signal to noise ratio of the difference signal is lousy unless the RF signal is very strong, and that corupts the Left and Right signal that we listen to.
You might recognize this system as the four channel LP that was tried about 30 years ago. The only good thing about that was that the phono pickup had to be good to 40KHz, and the resulting advances in phono pickup technology have benefited conventional stereo.
You might recognize this system as the four channel LP that was tried about 30 years ago. The only good thing about that was that the phono pickup had to be good to 40KHz, and the resulting advances in phono pickup technology have benefited conventional stereo.