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Re: PXL tapes
> Yep, some of the first prototype video tape recorders made by RCA and Bing
> Crosby Enterprises (BCE) in the early 1950's used a linear transport,
> before Ampex wowed them all with the helical scan transport in their
> recorder they introduced in 1956, and because of this landmark innovation,
> helical is what's used in video today.
You can read about the inventor of helical scanning, Earl Masterson, in
a recent issue of IEEE spectrum.
> The RCA prototype which came out around '52 or so used half-inch tape
> (Ampex used 2"), had humongous reels that had to be stopped by technicians
> using gloves (no joke!), and had a tape speed of around 300 ips. It
> actually produced good video, though, although the max recording time was
> about 15 minutes.
> Well, the PXL doesn't automatically adjust the tape speed according to the
> length of the tape to get 5 mins. on a side no matter what the length of
> the tape, you just get less recording time :). The figures you
No, I didn't think it does. :-)
I just didn't know if it is case A or case B because I don't have
a PXL. I am not a big fun of low resolution, I am a big fun of
high resolution. Both my camcorders are Sony Hi-8 and I edit into S-VHS.
I follow the PXL saga because of an unrealized dream I had as
a teenager: I wanted to design and build by own camcorder using
audio tapes. Pressure to do well in school never allowed me
enough time to implement that, but I did become an engineer anyway
and I went on to design bigger and better things...
> mentioned above for C-90 tapes are the correct specs, since PXLs are
> said to record 5 minutes of video/audio on a 90 minute cassette in the
> PXL2000 manual, although I timed it out once using 60 & 90 min. tapes, and
> I found that PXLs record 6 minutes 02 seconds of video per side on a 90
> min. tape, and about 3 minutes 55 seconds of video per side on a 60 min.
> tape, according to my findings.
My experience when I record a C-90 cassette on my cassette deck
that has a real time counter is that is usually goes for about
48 minutes per side. That tells us the PXL must run the tape
8 times faster, 15 ips.
> Well, after some experimenting, I found out that the PXL uses the right
> stereo channel of the tape for the video information, and the left channel
> of the tape for the audio information. I found this out by actually
> playing a PXL-recorded tape in a regular cassette player running at 1 7/8
> ips, and sure enough, the audio (which was slooooow, obviously) was on the
> left channel, and the video information (which had a quiet segmented
> buzzing sound at regular 1 7/8 ips speed) was in the right channel.
Thanks for the info, that covers it all. Obviously it was a lot easier
and cheaper for them to use a commercially available stereo head
instead of a custom multi-track head.
I was wondering if they used frequency multiplexing to record
different parts of the spectrum on different tracks. (Because
I had been thinking of doing that).
Obviously they don't as that would make the toy too complex,
probably more complex than a real camcorder!!
Apparently they only record the baseband, and that has to be
about 16K * 8 = 128KHz bandwidth, or about 6.5% of the bandwidth
of VHS. Given that VHS has 200 "lines of resolution" (forget the claimed
240 lines) from 2.5MHz bandwidth, the PXL recorder must achieve
a whopping 13 lines of resolution!!!
Would you recognize your friend's face if you recorded it on the
PXL audio tape? I really have to see this thing someday!!
<<alex kanaris>>
==============================================================================
Alexander Kanaris ___ ___ kanaris@bode.usc.edu
Electrical Engineering --- Systems / / /__ / kanaris@thales.usc.edu
University of Southern California /__/ ___/ /__ kanaris@girtab.usc.edu
Los Angeles, California 90089-2562 kanaris@alumni.caltech.edu
==============================================================================