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Spectrum Analyser CRT drive problem

Discussion in 'Electronic Repair' started by Hans Summers, Aug 9, 2003.

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  1. Hans Summers

    Hans Summers Guest

    I'm reposting this message here after advice on
    that video gurus congregated here...

    I am having a minor problem with the display on my spectrum analyser Mk2
    project, see
    .. The display for this analyser is an 4.5-inch ex-TV tube. I successfully
    dismantled that TV and rebuilt the necessary drivers etc as a miniature
    monitor having TTL-level video and composite sync inputs.

    Naturally the type of display this tube is now being subjected to is very
    different to a TV picture. There seem to be some problems with the video
    drive circuits, see pictures at the bottom of the above web page. The
    graticule fades out in the top eighth of the screen. Also see the "noise
    floor" photo which shows significant horizontal "bulge".

    Also there is a resolution problem - one spectrum analyser sweep consists of
    640 measurements, and I have a complicated interpolation circuit which
    "joins the dots" i.e. draws lines between the individual measurements, and
    also reduces the horizontal resolution to 320 pixels which I hoped would be
    displayable on the monitor. Problem is I can only get 160 horizontal pixels
    to display reliably - at 320 pixels a vertical line is very faint or
    invisible (depending on how much white there was in the preceeding
    microsecond or so's worth of scan line.

    The circuit diagram is also on that page
    ..pdf). I'm no TV expert. Can anyone suggest what modifications should be
    made to the video driver circuit to correct these problems?

    Hans G0UPL
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