cfogg@milton.u.washington.edu (Chad Fogg) (06/26/90)
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. According to the article, Production Services, Inc. of Tuscon, Arizona claims they can "squeeze a full-blown HDTV signal and a conventional NTSC signal within the same 6 MHz frequency channel" by using "a new modulation technology to add information to the spectrum without inter- ference." Richard Gerdes, PSI co-founder, explains that their technique "alters the shape of the carrier and transmits the result of that altered wave shape." 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. ---- Article aside, has anyone in Tuscon seen this? Any elaborations on waveform modulation; PSI's technology? And does WM have implications for other EM-based communications?
gary@ke4zv.UUCP (Gary Coffman) (06/27/90)
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
bill@videovax.tv.tek.com (William K. McFadden) (06/27/90)
This is the GENESYS system that was first introduced about two years ago. As I
recall, it stirred quite a controversy due to its "black magic" nature and
sketchy details as to how the system worked. A lot of engineers were claiming
it violated the laws of physics. I saw Mr. Geddes present a paper on the
system at the 1989 NAB convention. My coworkers and I couldn't tell if it was
real or snake oil. They also had a demonstration that wasn't working when I
went to see it. A coworker said they sort of got it working the next day
(apparently there was a lot of crosstalk between the two "channels").
At this year's NAB, another paper was presented that gave a lot more detail on
the system and outlined plans for testing it on the air. This time around, it
seemed more like a real system, but still had some "snake oil" aspects to it.
However, the jury is still out at least until the tests are completed.
Personally, I think it would be great if the system works, but you don't get
something for nothing. I think we'll have to give up something to get two
video broadcasts on the same channel. Whether it's something we're willing to
give up is another story.
--
Bill McFadden Tektronix, Inc. P.O. Box 500 MS 58-639 Beaverton, OR 97077
bill@videovax.tv.tek.com, {hplabs,uw-beaver,decvax}!tektronix!videovax!bill
Phone: (503) 627-6920 "The biggest difference between developing a missle
component and a toy is the 'cost constraint.'" -- John Anderson, Engineer, TI