Re: FS: Apple IIc Flat Panel Display Monitor

[mjmahon@aol.com (Michael J. Mahon)]

Tim Haynes replied:

>"Michael J. Mahon" <mjmahon@aol.com> wrote in message
>20040720024304.26045.00000125@mb-m28.aol.com">news:20040720024304.26045.00000125@mb-m28.aol.com...
>>
>> The AppleColor Composite monitor does a "trick" that is completely
>> non-standard:  it detects when the color burst is absent and boosts
>> the luminance video bandwidth to 10+ MHz, making an 80-column
>> display pretty good.  No "video" monitor will (or should) do this,
>> since there is never any useful signal there in a standard video signal.
>
>How hard would it be to make a box that does this (or would the TV just
>ignore the extra bandwidth?).  I have no idea what I'm talking about, but
>I'm imagining a black box that takes Apple II colour composite input and
>outputs luminance-boosted NTSC to a TV.  If I am smoking crack, please let
>me know.  :-)

Since the circuitry we are talking about is _inside_ the monitor, there
is no external box that can change it.

A video monitor is designed to a set of standards that are quite
specific about what is signal and what is interference.  Since
the FM sound carrier is at 4.5MHz in a broadcast composite video
signal (in the usual intercarrier sound detection system), video
monitors will remove signals above 4MHz from composite video
inputs.

Of course, unless comb filters are used (as they are in modern,
high quality monitors), frequencies above 3MHz will usually be
severely attenuated, since the chroma carrier is at 3.58MHz.

The only composite video monitor likely to support >4MHz
bandwidth is a monochrome monitor that expects a monochrome
video signal.

This is what makes the AppleColor Composite monitor so
special:  it is a color monitor when the burst is present, and
a wider bandwidth monochrome monitor when it is not.

It is possible in principle to modify a conventional color
monitor to defeat the video filters when the burst is absent,
but doing so would be a different problem for each monitor,
and quite difficult on some.

-michael

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