Aucbvax.1349
fa.human-nets
utzoo!duke!mhtsa!ucbvax!DERWAY@MIT-ML
Thu May 14 22:03:01 1981
HUMAN-NETS Digest V3 #100
HUMAN-NETS AM Digest Friday, 15 May 1981 Volume 3 : Issue 100
Today's Topics:
Query Replies - WHT and Cable & No Calorie Sugar
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Date: 12 May 1981 12:43 cdt
From: Phinney at HI-Multics (Tom Phinney)
Subject: Question about WHT and cable
WHT apparently uses the same technique as other companies in the
pay-TV trade. The video signal is "scrambled" by mixing the true video
with a sine wave phase-locked to the video's horizontal line rate,
15734 Hz. The sine wave has its greatest amplitude at the left edge of
the "line" of the true video signal, which is where the line sync
information is normally found. Line sync is determined by the lowest
amplitude point in the video signal, so adding this phase-locked sine
wave causes the TV circuitry to locate a false sync somewhere in the
middle of the normal picture. This causes the displayed picture to be
rotated by about half a screen width, more or less depending on the
amplitude of the original mid-screen video information.
The sound is "hidden" by using a technique similar to the
"storecasting" approach used by many FM stations -- a high-frequency
subcarrier (87 KHz if I remember correctly) is added to the normal
audio, which in your case is the pay-tv advertisement, and the desired
audio signal is used to FM modulate that subcarrier. This means that
the received signal must be demodulated twice to recover the "hidden"
audio, once to recover the video and wide-band audio, and a second
time to recover the "hidden" audio. As I recall, the 15734 Hz sine
wave is also mixed with that recovered audio signal (and filtered out
by a low-pass filter in your TV receiver), so that the pay-tv decoder
just mixes the recovered sine wave (inverted) with the video signal to
unscramble it.
Home-made decoders to unscramble these signals are possible, and are
fairly easy if your TV is old enough that the available signals are
not buried inside an IC. In that case you can make a demodulator with
about five ICs, and put it inside your TV. Otherwise you have to add
the RF front-end to the system, and that's a fair amount of trouble,
because you need to supply some form of AFC (automatic frequency
control) to the UHF front end to get stable reception on the channel.
There are people in most of the major semiconductor manufacturing
areas (Silicon Valley, Phoenix, Austin) who make these decoders as a
side business, and you might be able to locate one through local
residents. Otherwise check out the local pirate-tv outlet in your
neighborhood. The cable TV guys hate the pirates and sue them all the
time, so don't look for a listing in your yellow pages.
I hope this has helped a little. Tom Phinney
------------------------------
Date: 12 May 1981 00:05:58-PDT
From: ihnss!karn at Berkeley
Subject: Pay TV decoders
I believe the Channel 68 pay TV scheme in use in Northern NJ is ON-TV,
the most famous of the over-the-air subscription TV systems.
ON-TV is being run over Channel 44 here in Chicago, and a number of us
have built decoders to receive it. This is how the signal is encoded:
The modulated video carrier is itself amplitude modulated with a 15734
hz sine wave phase locked to horizontal scanning. The sine wave is
phased such that the horizontal sync pulses occur in the "valleys" of
the sine wave. Since horizontal sync is normally supposed to occur at
maximum carrier level, the TV set (without decoder) triggers on random
video in the middle of the scan line. Thus you get the wavy vertical
black bar (horizontal sync) down the center of your screen.
The same sine wave is also amplitude modulated on the sound subcarrier
(remember, the sound carrier is normally only frequency modulated with
the sound, so the two don't interfere.) The decoder must amplitude
demodulate the sound carrier, filter the sine wave, and AM the
received video signal, usually by sending it back into the receiver's
AGC stage. Note that phase locked loops won't work, as the sine wave
is gated off during the vertical interval.
The sound is placed on a 63 khz FM subcarrier, which in turn modulates
the main FM sound carrier. This technique is identical to the SCA
system used by FM broadcast stations to transmit MUZAK or similar
worthless programming. The sound is easily received with a 565 PLL or
equivalent at the sound discriminator output. The audio "baseband" is
available for use as a "barker" channel ("Look what you're missing by
not being an ON-TV subscriber..call 555-1212, etc") but it isn't used
here except for hourly station ID's.
There are a rapidly increasing number of companies selling boards and
kits for ON-TV decoding. They are NOT selling, for the most part,
completed, working units, as this keeps them out of trouble
(especially in California).
Phil
------------------------------
Date: 05/11/81 07:38:49
From: PCR@MIT-MC
Subject: left handed sugar
I don't know about the rest of you, but I was reading about
left-handed food and how it wasn't any good for nutrition 10-15 years
ago. The idea is an old standard in science fiction.
...phil
------------------------------
Date: 10 May 1981 09:16-EDT
From: Robert Elton Maas <REM MIT-MC AT>
Subject: No-Cal Sugar
(1) The use of the term "natural" for this mirror-reverse of sugar
(sucrose??), and the claim it's chemical identical to normal sugar,
are abuse of the language. Most of the biological mechanisms for
processing food and other chemicals in the body are specific to the
handedness of the chemical being processed. I'm not a biochemical
expert, but I would guess a lot of processing sites in the body would
get confused by this un-sugar, perhaps "recognizing" it as some other
chemical and attempting to perform chemical transformations on it that
weren't appropriate. I'd think that detoxifying mechanisms would have
trouble with it, and it could easily be cancerous. Can some
biochemical expert speculate further?
(2) There have long been science fiction stories about somebody
traveling around the universe or through some broken transporter
device and coming back reversed and starving because all the food was
backwards for this traveler. Looks like sci-fi has started to become
reality. Soon (30 years?) we'll be making complete DNA and life in
reverse, growing food that only reversed creatures cn eat. Imagine
the CIA arranging that wheat we sell to the USSR is reversed. It
bakes nice looking bread that doesn't support life. I wonder why
reversed sugar tastes sweet? Does the tongue measure just the gross
chemical characteristics instead of looking specifically for sugar
compounds? (For salt and sour tastes it obviusly does just measure
ionic charge balance or somesuch. But bitter and sweet I don't know
about.) Would reversed-wheat taste like wheat, or are smell receptors
more sensitive to handedness?
(3) Some of that probably is outside the subject of HUMAN-NETS, but
I'm not sure it belongs in SCI-FI-LOVERS either. Oh well. Someday
we'll have a real HUMAN-NET with threaded multi-term indexing and
keyword profiles for each user, instead of discrete mailing lists...
maybe.
(4) Reverse-handed sugar has been known for decades. How can anybody
patent it? It must be some commercially feasible way to make it that
got patened, not the chemical itself, right?
------------------------------
Date: 10 May 1981 (Sunday) 1110-EDT
From: MOSESJ (Jack Moses)
Subject: no-cal sugar....an uninformed opinion
The "L" stands for the Levo-rotary isomer of sucrose which, when
passed through a Polarized filter, will cause light to turn to the
left (rather than the commonly occuring dextro variety which turns
light to the right). The isomeric properties of most compounds is an
extablished fact; thus one must conclude that since L-sugar does exist
in nature, it would be ludicrous for the agency to issue a patent on a
naturally existing substance.
The patent must have been issued for the PROCESS that created the
substance; and therein lies a formidable problem. In organic
chemistry a slight alteration of the flowchart sequence will allow
competitors to produce the compound without infringement. So much for
the value of the patent itself.
I am not in a position to pass judgement on the medicinal, social or
economical value of the L-sugar itself, not having any info on same,
but the value of the isomeric properties is exemplified in the example
of a familiar (to most of us) Eli Lilly product known as Darvon. In
it's Dextro-rotary form, Darvon in a non-narcotic pain reliever which
acts on the synapse of certain nerves associated with pain, thus
producing relief. But when Lilly made a Levo-rotary isomer of the
same compound, it acted on the sinus node to inhibit the production of
histamines, thus offering relief from colds. This product was
appropriately named NOVRAD (Darvon backwards) .... an antihistamine.
So much for the organic stuff....now if the subject matter was
regarding the stock market (that is my REAL bag) drop me a line.
Jack
------------------------------
Date: 11 May 1981 0744-PDT
Subject: No-Cal Sugar
From: ADPSC at USC-ISI
(1) I agree that the term "natural" is a bit overused. If we are to
use the broadest definition, then anything could be called natural.
It is one of those terms which I have begun to more or less ignore in
its usual context, assuming that the term desired was "organic".
Perhaps Edwin Newman will choose to deal with this one if he hasn't
already.
(2) It appears that just the process for producing this "new" sugar
was patented. Knowledge of these substances has been around for many
years. The problem arose in trying to find commercially feasible
production methods. Apparently Biospherics feels it has found such a
process. I read most of the article as so much hype.
(3) From what little I know of sugars (not being a biochem-type), and
from what my friends have been able to get through to my non-biochem
oriented brain, "normal" and the "left-hand" sugars might be (very
simplistically) pictured as:
A B A
Normal CCCCC Left CCCCC
B
The body recognizes the A's and C's in taste, but looks for the B's
only in digestion. As a friend of mine put it, other things often get
mistaken for sugars, but sugars seldom get mistaken for much else. As
such, the potential for causing cancer is minimal. Again, not being a
biochem-type, I don't know how bacteria reacts to this stuff, so I
can't form a good opinion on the tooth decay issue.
(4) The problem of applicability of mailing list of course exists.
Too much stuff doesn't seem to fit adequately into HN or SFL. I'm
open to any suggestions on that one.
Don
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