Help needed on radio theory

Discussion in 'General Electronics Chat' started by poriet, May 29, 2012.

  1. poriet

    Thread Starter Member

    Feb 26, 2010
    Hello guys,
    This may be a tricky one:
    I want to rewind my own IF transformers for 455KHz because I'm interested in making some superhet receivers which are nothing to do with listening to the radio.
    I do have a number of unanswered questions, but, rather than bore you all to death, I'll try this a step at a time.
    Incidentally, the only manufacturer of these things (Toko ) ceased production long ago. Mouser sell them, but I'm in the UK which makes life difficult ( even more so after the banks in the USA bankrupted us! ). Some constructors salvage them from radios, but use them without really knowing exactly what's inside. In any case, I want to actually rewind them myself so I know exactly what I've got. For a frequency around 500KHz you need around 150 turns of v thin wire: not an impossible job IMO. The tricky bit is deciding where to 'tap' the primary winding.
    Even after an exhaustive Web search I've only found 2 sites which attempt to explain the theory. One is Swedish and I cant follow it: the other has calculations which make no sense and the author wont answer his emails. Is somebody trying to tell me something?
    I can elucidate about the Mouser coils if anyone out there is sufficiently expert on radio theory to help,

  2. davebee

    Well-Known Member

    Oct 22, 2008
    I think you need to think about them more as filter elements than as simply transformers.

    Their primary use is to set the bandwidth of the radio signal so the modulated audio of one station is passed and the audio of adjacent stations are rejected.

    Adjusting the tap location will affect the input and output impedance match, but you also can adjust how tightly the two coils are linked fluxwise, and whether each coil is tuned right on 455 kHz or is slightly offset above and below 455 to create the passband and reject bands to fit the bandwidth of the audio signals that need to be passed and rejected.

    It will probably be easy to make IF transformers that work to some extent. The tricky part would be if you wanted to fine tune them to pass the highest audio frequencies that you need to pass, while rejecting adjacent signals that you need to reject.
  3. poriet

    Thread Starter Member

    Feb 26, 2010
    Hello Dave and thanks for the reply. I have been away, so that is why this reply is so late.
    There may be a more appropriate forum for this type of query: would you know?
    I think I will leave this and repost when I have a more specific question.

  4. radiohead

    Distinguished Member

    May 28, 2009
    Here is a site that has coils and inductor-related products. If you contact them, they might be able to answer some of your questions or guide you to the answer.
  5. #12


    Nov 30, 2010
  6. bertus


    Apr 5, 2008
  7. poriet

    Thread Starter Member

    Feb 26, 2010
    Thanks guys: I've registered with a vintage radio forum.