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What does this mean ?

Discussion in 'Electronic Repair' started by Volk, Sep 23, 2003.

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  1. Volk

    Volk Guest

    Referring to the SCA1 Subcarrier Adapter. With that unit you have to connect
    to the baseband demodulated signal inside your radio unless your radio has a
    dedicated SCA output such as is found on our FR1 kit. The only way to find
    the baseband signal is to consult the schematic for the radio you intend to
    use.
    ------------------------------------------------------------------------------
     
  2. No.

    After the FM demodulator inside the tuner you will find a signal, the
    baseband signal, with the following components (view with fixed width font)

    ^
    | _________ _________ _________
    |/ \|/ \/ \ | | |
    +---------------------------------------------------------------------> F (Hz)
    a b c1 c2 d e f

    a) Audio Left+Right (mono)
    b) Stereo pilot tone at 19kHz
    c) Left-Right modulated on a 38kHz carrier (carrier removed)
    d) RDS carrier at 57kHz
    e) SCA carrier at 67kHz
    f) SCA carrier at 92kHz

    In a normal tuner this baseband signal is directly connected to the stereo
    decoder. The stereo decoder takes the pilot tone and recreates the 38kHz
    carrier using a phase locked loop, demodulates the Left-Right signal,
    extracts the Left and Right signals using Left+Right and Left-Right. A
    low pass filter then removes the pilot tone and everything above it. You
    will find very little, if any, SCA carriers in the line level outputs of
    a tuner.

    +----------------+ +----------------+ Left +----+
    | | Baseband signal | +--------+ LP +--- L
    --+ FM demodulator +-------+---------+ Stereo decoder | Right +----+
    | | | | +--------+ LP +--- R
    +----------------+ | +----------------+ +----+
    |
    +-------------------------------------------- B

    You need the schematic of your radio to find the place to bring out the
    baseband signal. I had to do this to my tuner (added one phono socket)
    to attach an external RDS decoder.
     
  3. Dbowey

    Dbowey Guest

    Ho^3 posted:
    << Referring to the SCA1 Subcarrier Adapter. With that unit you have to connect
    to the baseband demodulated signal inside your radio unless your radio has a
    dedicated SCA output such as is found on our FR1 kit. The only way to find
    the baseband signal is to consult the schematic for the radio you intend to
    use.
    ------------------------------------------------------------------------------
    -------------------------------------------

    ........ connect to the baseband demodulated signal .... ??????????

    Is that connection the same as the (tape out) ?? >>


    No. It means you need to tap into the received signal at the discriminator
    output, and ahead of the de-emphasis net, etc.

    Don
     
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