Re: 80-column text display on TV set

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

Ed Eastman wrote:

>I personally have found that newer TVs do better than older ones.  No TV 
>does 80 column text well, but many do it sufficiently.  The picture 
>tubes these days are better quality (sharper picture) and the digital 
>circuitry seems better able to handle the extremely complex composite 
>signals from the Apple II.

The critical difference in newer/costlier TVs is the use of a comb filter
to separate the chroma and luminance components of the composite
video signal.  This allows the full luminance bandwidth to be used in
the display (though many displays will not preserve luminance bandwidth
beyond 4.2MHz because in the broadcast world, they expect the audio
subcarrier to be at 4.5MHz, and you don't want _that_ in the picture.).

Older sets used simple bandpass filters, and the result was that the
luminance bandwidth was limited to less than 3.5MHz--not really
enough for 80-column text (over 500 pixels per line).

Apple II video, though slightly non-standard in the sync fields, has
good bandwidth--better than 14MHz in the luminance--so a newer
TV could do a pretty good job of extracting the "edges".

Of course, if the burst is on the color artifacting may make the
text hard on the eyes, at least.

-michael

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