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These Delay Lines: what are they?

Discussion in 'Electronic Basics' started by Fred Abse, Nov 9, 2003.

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  1. Fred Abse

    Fred Abse Guest

  2. Baphomet

    Baphomet Guest

    They are used to ensure that the video and chroma signals register (overlap,
    coincide) by adding a predictable amount of time delay to the chroma signal
    before recombining into a composite (I think).
  3. Baphomet

    Baphomet Guest

    a.. Component Video. There are two component-video formats; color difference
    (Y, Pb, and Pr) found in broadcast and luma/chroma (Y-C), or S-VHS, found in
    VCRs. Both have a luma (Y) bandwidth that's greater than the color (Pb/Pr or
    C) bandwidth making it difficult to keep the signals time-coincident.
    a.. They are used to ensure that the video and chroma signals register
    coincide) by adding a predictable amount of time delay to the luminance (Y)
    before recombining into a composite.
  4. Jim

    Jim Guest

    Over time I've salvaged a number of delay lines from VCR's and other
    equipment and would like to know what they are.

    They are small, thin plastic boxes of various lengths and heights and have
    3 leads. Inside each is what looks like a piece of glass or ceramic with
    wires from the 3 leads connected to gold pads on the edges of the glass.
    Some are made by KSS and others by Asahi Glass Co. but I can't seem to find
    descriptions of these on the web.

    How do these work, and what would they be used for? Are they for the same
    use as semicinductor delay lines?

  5. Lord Garth

    Lord Garth Guest

    There is a possibility you could have a Surface Acoustic Wave device. A SAW
    filter would appear to have interlaced 'fingers' on a substrate of glass.
  6. Fred Abse

    Fred Abse Guest

    The point I was making was that the OP stated that he could not find any
    answers on the Web. This appears to contradict my experience. there is, in
    fact, a large amount of information on the subject out there.
  7. ddwyer

    ddwyer Guest

    They are bulk acoustic delay lines
    The bulk material is a special glass with zero temperature coefficient
    of delay.
    The path is folded so that the line is as small as possible.
    Conversion from electrical to acoustic energy and the reverse is by
    piezoceramic transducers generally the operating frequency is in the
    range 1 to 10MHz.
    In PAL TV s a delay line stores one picture line.

    Digital processing now replaces these lines.
    The first acoustic line I saw stored one picture frame for NSTC to PAL
    Over a period of 25 years the lines got cheaper and smaller, the one you
    saw was probably a slice from a single block cut like bread into 100s of
  8. Jim

    Jim Guest

    Tru words? Useless answers!!
  9. I wonder:
    * Is it posible to make an oscillator where the frequens is depended of a
    delay line? If so, is there a scheme on the net, or can some smart person
    draw an example?
    * Same question, but for an ceramic filter.?

    And of course, The pin asignment. How to couple one if i want to delay a
  10. ddwyer

    ddwyer Guest

    Yes an oscillator can be made employing glass bulk acoustic delay lines
    the frequency of oscillation will be 1/delay time however the centre
    frequency of the response will be 3MHz and the delay 1/64? vsec ie the
    length of one TV line.
    Hence or other wise the oscillator can be made to lock every 16kHz or so
    The delay lines when matched will have a loss between 12 and 20db so the
    amplifier must have a gain exceeding this.
    The best way to make an oscillator that jumps every 16kHz centered on
    3MHz will be to make it a tuned amplifier and tune across the band.
  11. Fred Abse

    Fred Abse Guest

    If it's PAL, it's 63.943 usec. (An integer number of periods at 4.43361875

    God only knows how I dredged that up from memory, it's been hiding in
    there a quarter century :)
  12. 'bout time you let it out! ;-)
  13. Fred Abse

    Fred Abse Guest

    Sorry, it's half-periods (just went and looked it up)
  14. Then i guess I can do it this way (Make sense if seen in fixed font):

    | |
    | +------------+ +-----------+ +-----------------+ |
    +--| Delay line |--------| Amplifier |------| Schmitt trigger |---+
    +------------+ +-----------+ +-----------------+

    Where either the amplifier or the schmittrigger (but not both) invert the
  15. ddwyer

    ddwyer Guest

    If its a pal line tune the input and output transducers with inductors
    to give overall loss of 12 to 20db.
    AC amplifier gain greater than 20db centered on 4ish MHz without
    schmitt to set in oscillation try to keep the transfer function linear
    ie no schmitt in the loop.
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