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Are Walkman radios superhets?

Discussion in 'Misc Electronics' started by Cass Lewart, Dec 7, 2003.

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  1. Cass Lewart

    Cass Lewart Guest

    I wonder if the walkman type AM/FM radios are superhets. I took one
    apart and could not find any IF transformers. Same would apply to 400
    MHz FRS band walkie talkies. I could not find a schematic.

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  2. CWatters

    CWatters Guest

  3. I've answered this thread elsewhere, months ago.

    Certainly, those cheap FM only two button radios use a variant on the
    Phillips TDA7000, ie a conversion to a very low IF frequency where
    an active filter supplies the IF selectivity.

    And it's slightly possible that some cheap AM radios use the later
    variant on the old Plessey ZN414 (I think I got the prefix wrong)
    TRF IC. Certainly, in the Phillips datasheet for the IC (I forget
    the number offhand, something like a 7088) in those two button radios,
    they show in one schematic circuitry for an AM section, and it's something
    like those TRF ICs. Certainly, they must be used somewhere, since
    they are being made.

    I have no idea if such schemes are actually being used in "Walkmans"
    though if they are, likely it's limited to the cheap ones.

    I've opened up recent tiny cellphones, and hardly any of it is
    recognizeable, let alone reusable. I suspect that's the case
    in FRS radios. In the old 49MHz superhet walkie talkies, they
    had fairly decent receivers; certainly they were the same basic
    scheme used in a lot of low deviation FM receivers, dual conversion
    with a wide ceramic filter at 10.7MHz and a ceramic filter at 455KHz.
    I can't see them going to something inferior as they move up in frequency,
    especially considering the FRS tend to be more expensive. It's just
    that they use surface mount to make manufacturing cheap, and once
    something becomes surface mount it's not nearly as identifiable
    as those big green or orange filters of days gone by.

    Michael
     
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