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From: gary@ke4zv.UUCP (Gary Coffman)
Newsgroups: rec.video,sci.electronics,rec.ham-radio
Subject: Re: HDTV and Waveform Modulation
Keywords: HDTV waveform PSI
Message-ID: <811@ke4zv.UUCP>
Date: 26 Jun 90 22:13:45 GMT
References: <4454@milton.u.washington.edu>
Reply-To: gary@ke4zv.UUCP (Gary Coffman)
Followup-To: rec.video
Organization: none
Lines: 49

In article <4454@milton.u.washington.edu> cfogg@milton.u.washington.edu (Chad Fogg) writes:
>A new term to add to the HDTV glossary, waveform modulation is given
>a brief mention in the July 1990 issue of _Video_Magazine_, page 50.
>
>Richard Gerdes, PSI co-founder, explains that their technique "alters
>the shape of the carrier and transmits the result of that altered wave
>shape."

This is called "modulation" and is what all transmitters do to convey
intelligence on a carrier.

>At the NTSC level:
>
>   PSI gas already developed a commercial product using waveform modulation
>   for NTSC broadcasts: an encoder and decoder that allows an NTSC station
>   to broadcast two channels simultaneously from one transmitter.  "You
>   could tune to channel 4A or 4B using the decoder," Gerdes says.  The
>   FCC has already granted an experimental license for channel 11 in Tuscon,
>   a Fox Network affiliate, to begin testing the system.
>

This technology is not new and has been used on satellite video channels
for several years. Basically what they do is break apart two NTSC pictures
and use field one from one picture and field two from the other. They then
reverse the field sequence for the next frame. Then at
the receiving end they use two framestores and a demultiplexer to 
reconstruct the two video signals. As you can tell from the description,
they throw away half of each video frame. This causes some loss of 
vertical resolution (though they do frame to frame interpolation which
recovers most of the resolution for stationary pictures). The resulting
artifacts are most noticable on rapidly moving video.

One thing video freaks should know is that broadcasters have expressed
a serious lack of interest in HDTV. In fact the use of minicams and
small format tape has markedly reduced the quality of ordinary NTSC
video being broadcast by networks and affiliates. The over the air
broadcaster has seen a decline in viewership in the last several years
due to low quality VCRs and poor quality NTSC cable channels being
preferred by the average viewer. The broadcaster has responded by
cutting costs to the bone by using cheaper equipment and reducing
the technical requirements for his staff. It is estimated that it
will cost over $50 million to changeover a broadcast plant to HDTV.
With no market (no receivers in place) and the loss of NTSC viewers
(estimated $120 billion invested in NTSC infrastructure) the broadcaster
would have to have deep pockets indeed to pioneer HDTV. Plus there
is no HDTV product available to fill those 24 hours a day.

Gary KE4ZV
Senior Engineer WXIA-TV