L - R

Discussion in 'General Electronics Chat' started by AnalogKid, Apr 21, 2015.

  1. AnalogKid

    Thread Starter AAC Fanatic!

    Aug 1, 2013
    I meant to post this last Sunday morning. oops.

    (L + R) + (L - R) = 2L
    (L + R) - (L - R) = 2R

    The two camps were quantity versus quality. Longer-distance reception meant a larger listening area and more listeners per transmitter, which meant more revenue even if the signals were distorted out in the boonies. Higher signal quality took more energy and reduced the listening area, but the signal was clean right up to the point where it dropped out. The historical ancestry of the two camps told the whole story – the quantity of cash team was led by GE, founded by Edison, while the quality of art team was led by Crosby-Teletronics, as in Bing Crosby. OBTW, Bing liked tech; he funded the development of professional quality audio *and* video recording. The famous Ampex 202's at Sun Records in Nashville - Bing did that.

    In 1946 the FCC moved the FM broadcast band from around 50 MHz to around 100 MHz where it is today. That instantly obsoleted a lot of radios and honked off a lot of relatively wealthy people, a bumpy ride for the agency.

    Because of that history, a mandatory requirement of any FM stereo system was perfect reverse compatibility with the much larger number of radios that had been purchased since the move. To achieve this, all competing systems actually had two signals, the original mono signal that now was the sum of the two stereo channels, and a 2nd signal (called the difference signal) on a subcarrier that the radio used to reconstitute the separate left and right stereo channels (see above). Even though the overall signal was FM, the GE system had an AM subcarrier that faded out over distance and was subject to all of the noise and distortion of any AM signal (the noises and distortions that prompted Armstrong to invent FM in the first place). The Crosby system had an FM subcarrier so there was no loss of the stereo image at long distances; either the full stereo signal was present, or the whole thing dropped out. In the fringe reception areas, the bouncing on and off Crosby signal was judged to be less pleasant than the GE signal that faded in and out with static.

    Because there was a lot of money on the table there was a lot of money under the table, dragging out the fight for over five years. Finally, at 10:00 am. on Wednesday, April 19, 1961, the FCC released its Final Order selecting the Zenith/GE system over the Crosby system as the FM stereophonic broadcasting standard. At 9:59 am., Crosby-Teletronics stock was worth $15 a share; by 2:00 P.M. that afternoon it was down to less than $2.50.

    That system continues to be used today for stereo FM broadcasting, which accounts for the poor quality of stereo signals in comparison with monaural signals. When reception is poor, the stereo AM GE/Zenith signal typically fades in and out, while the monaural FM signal remains relatively strong. This manifests itself as the "STEREO" light flickering on and off (on radios old enough to have one).

    While known as WRVE since March 1994, this station has a long history as one of the nation's pioneering FM radio stations. A byproduct of the station being owned by General Electric with similarly pioneering sisters WGY (AM) and WRGB (TV), WRVE traces its history to W2XDA Schenectady and W2XOY New Scotland, New York - two experimental frequency modulation transmitters on 48.5 MHz, which signed on in 1939. The two were merged into one station with the W2XOY call-letters on November 20, 1940 with the station taking the WGFM call-letters in the late 1940s, and moving to 99.5 MHz when the FM band was relocated to the 88-108 MHz portion of the radio spectrum. On June 1, 1961, at 12:01 a.m., WGFM became the first FM station in the United States to broadcast in stereo.