Format of a stereo station

Discussion in 'Wireless & RF Design' started by mik3ca, Feb 25, 2008.

  1. mik3ca

    Thread Starter Active Member

    Feb 11, 2007
    189
    0
    My super-regen receiver is functioning better, and I think I am picking up stereo.

    I will explain what happens.

    I start my receiver at the end of 102.9Mhz (local station). As I turn my tuning knob very slowly, 102.9Mhz fades out, and then 103.5Mhz comes in. After another slight turn, I get nothing (It almost sounds like someone has hid a transmitter in my room running no music at that frequency). After another slight turn, I get 103.5Mhz in again. So all together, I get the same station in twice.

    This makes me think that I can receive stereo. Why? because I think the first time I can pick up 103.5, I picked up the right-channel, and the second time I picked it up, I picked up the left-channel, and I think that dead silence in-between is actually a special signal that indicates I'm receiving stereo.

    can someone please clarify this for me?

    I'm thinking of adding a stereo detection section to my superregen. That is something I will have to figure out, since I only want to use one tuning control.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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  3. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Your super-regen radio does not have an FM detector. It has an AM detector and it uses slope detection to detect FM.
    It tunes to one side and one slope of the signal from the FM radio station's signal and the AM detector in the radio detects the mono audio signal from the slope. Then you tune to the peak where there is no slope so there is no AM and your radio is quiet. Then you tune to the other slope of the signal and your radio detects the AM caused by the slope.

    Tuning of the radio station has nothing to do with FM stereo.
    FM stereo is multiplexed. The mono L + R is from 50Hz to 15kHz. There is a 19kHz pilot for the multiplex to sync with. Then the L - R is AM modulated with a suppressed 38kHz carrier with sidebands from 23kHz to 53kHz. A circuit detects the L - R and adds L + R with L - R to obtain the left channel and it subtracts L - R from L + R to obtain the right channel.
     
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