Posted by Bill Vermillion on 01/22/07 17:45

In article <cc9qp2trt7230sogp60odumgrpu0acbp2e@4ax.com>,
chrisv <chrisv@nospam.invalid> wrote:
>JoeBloe wrote:
>
>>LD is too huge, too bulky, and it presents the hardware designers
>>with too many technical hurdles to make good gear for it. The wobble
>>at the edge of a twelve inch platter can be huge.
>
>Too bad that the market didn't go for the "needle and groove" video
>disk that RCA tried to make work, eh?

The 'needle and groove' was mis-understood by most - thinking it
was similar to LPs. Actually the groove was used to move the
stylus across the disk while the data was capactiance encoded
beneath the groove.

The arm would track the groove and when it got a certain distance
from being exactly perpendicular to the track, the rotating bar at
the back moved the arm to the position where it was perpendicual
again. There were a couple of audio turntables that used this
approach.

It was basically a cheap way to act as a servo control. So it was
essential a mechanical servo. The JVC VHD format used 10" disks
with capacitance encoding, but also embeded the servo track
eletrically so that the disk was flat. And the 10" disk of JVC
played for the same lenght of time the RCA CED did.

What I found interesting at a demo of the VHD at a CES show - prior
to it's release [which was never brought to the US as they knew
that TRHEE competing disk technologies would problaby mean they
would all fail] was that there were four information channels.

You could - if you wished - run three video channels - each in a
still mode and one audio channel - and thus emulate the then
popular three screen slide show presentations. Or you could make a
move in stereo, or even have 3 audio channels.

At that same show they demonstarted a digital recorder - using the
exact ouside format of the Philips Compact Cassette - but purely
digital. The RDAT was in development at that time, and that format
went away - as did the Philips 1/4" reel-reel digital tape recorder
that had seven parallel digital tracks to build an audio output.

The reels could be flipped and played the other direction as the
tracks were intereleaved much in the same fashion as 1/4 track
tapes were. That meant there were 14 tracks on the 1/4" tape.

They used a head design that was more simliar to current heads in
hard-drives, as there was NO WAY they could have enough room for
7 coils using the induction method of all analog tape recorders.

Bill

--
Bill Vermillion - bv @ wjv . com

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