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question about an AM demodulator IC ?

Discussion in 'Radio and Communications' started by patric44, Aug 3, 2017.

  1. patric44

    patric44 New Member

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    hello guys

    i found in my electronics salvage an old ic its a TDA3845 when i searched for it and looked at the datasheet i saw that its
    a Quasi split-sound circuit and AM demodulator .
    so my question is :

    1- what is Quasi split mean ??
    2- i was wondering can i use it to make an AM or FM radio or something ?

    i saw a circuit for the ic and its seems very simple
    [​IMG]
    so what exactly is it (it seems more like a radio to me ) ?
     
    Last edited: Aug 5, 2017
  2. JimB

    JimB Super Moderator Most Helpful Member

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    1- what is Quasi split mean ??
    Quasi Split Sound is a way of describing the NICAM stereo transmission system.
    From Wikipedia:
    For more information, look at the link:
    https://en.wikipedia.org/wiki/NICAM


    Yes, that should be possible.

    JimB
     
  3. patric44

    patric44 New Member

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    thanks jimB .

    so the ic was designed to receive NICAM packet audio transmission for the tv ?
    so most of the tv audio transmisstion is NICAM ? and is there a radio broadcasts using the same protocol ?
    can i use that to receive tv brodcasts (the sound only ) ?


    and how i will modify it to receive AM ?
    so i have to make a local oscillator and mixer circuit to produce the IF then feed it to the ic
    and change the LC thank circuit for AM ?or what

    sorry i have a lot of questions :), i realy appreciate your help
     
  4. dave

    Dave New Member

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  5. JimB

    JimB Super Moderator Most Helpful Member

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    In the UK, analogue UHF TV had nicam stereo sound.
    The basic TV sound signal was FM, the nicam part made it into stereo for receivers which were equipped to decode it.
    All UK TV is now digital, the analogue and NICAM are gone.

    Not in the UK.

    Yes, I think so.

    Maybe use the AM output from the chip?
    I don't know.

    Yes.

    If you mean Medium Wave (550 to 1600kHz), yes.

    JimB
     
  6. patric44

    patric44 New Member

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    thank you so much

    i will try the circuit above with a local oscillator and the mixer and see what will happen . wish me luck:)
     
  7. patric44

    patric44 New Member

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    it didn't work , any suggested circuit ?
     
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Have you used all the required components, what about the IF transformers and ceramic filter?.
     
  9. patric44

    patric44 New Member

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    Oh sorry, you've got so many similar threads going I got confused with one of your others.
     
    Last edited by a moderator: Aug 5, 2017
  10. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    The one in the datasheet - the circuit that makes the IC work!!.
     
  11. patric44

    patric44 New Member

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    iam sorry i thought you ment the circuit above .
    actualy i connected an internal (oscillator - mixer - IF amp ) from another ic i have to the TDA3845 theoreticly it should work
    but it didnt i heared just a hissing sound !?


    iam sorry but why my previos comment has changed:cool: i dindt mean any thing just was asking !?
     
  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I don't really see why you're playing with this chip, it's NOT a radio chip, it's a TV one.

    It 'might' be possible to use some parts of it to help build a radio?, but it's likely to be pretty difficult as there won't be any data out there about doing so.
     
  13. patric44

    patric44 New Member

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    you are propaply right , but i thougt it would be very cool if i had a tv sound broadcast receiver .
    but propaply its easier to just wach the tv .
     
  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    But you wouldn't, analogue TV ended a while back.
     
  15. patric44

    patric44 New Member

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    me :can i use that to receive tv brodcasts (the sound only ) ?
    JimB: Yes, I think so.

    "i think so " from JimB ,
    gave me a little motivation to try the circuit , but no problem ( building and experimenting with radio circuit is one of my true passions )
     
  16. JimB

    JimB Super Moderator Most Helpful Member

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    Yes, I did say that didn't I.

    But, you have to use all the appropriate parts:
    Signal frequency tuned circuits and an RF amplifier to give the required sensitivity.
    A mixer and local oscillator to convert the signal frequency to the intermediate frequency.
    A suitable IF filter to give the required selectivity.
    An audio amplifier to give enough power to drive the loudspeaker.

    JimB
     
  17. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    And how does all that decode the digital TV signals?.

    However, he's now mentioned (elsewhere?) that he's in Egypt, and I've no idea if they have gone digital or not?.
     
  18. JimB

    JimB Super Moderator Most Helpful Member

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    It does not, I never said that it would.
    Have a look at post #4 of this thread for my best attempts to give a positive/definitive reply to the OPs questions which may have lead to some experimentation for him, rather than a wet blanket "Oooh, you can't do that!" kind of reply.

    Neither do I.

    By the way, I had sussed out that he was in Egypt right at the start.

    JimB
     

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