thinking back......

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dacflyer
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thinking back......

Post by dacflyer » Wed Sep 03, 2008 6:25 pm

does anyone remember ever seeing at the top of the tv screen, some dots and dashes moving etc.. i was told long ago that it was a sort of data stream. does anyone know anything about that ? if the vertical size was not exactly right you could easily see it. it was typically at the top of the screen.. but not seen on all channels. just certain ones.
i am currious what all that data was for and or what it did..
was it like side band ,like some radio stations have
( SCA i think its called. )

just currious.

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Externet
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Post by Externet » Wed Sep 03, 2008 6:35 pm

Hmmm... Teletext - closed caption data ?
- Abolish the deciBel ! -

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Post by rshayes » Thu Sep 04, 2008 1:18 am

Originally, a few lines during the vertical retrace interval were sometims used for a Vertical Interval Test Signal (VITS). These were usually single line analog test patterns (such as multiburst, stairstep, color bar, sine-squared, etc.). These would be observed on a waveform monitor to check for degradation of the video signal as it passed through various signal channels. The waveform monitor had special synchronization circuits wich allowed it to pick out any individual line and display it like an oscilloscope.

Eventually, digital signals were also inserted in some of these lines. Some of the pay TV systems used such a digital code to transmit information to their decoder boxes. Another use for these signals is to transmit closed caption data.

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Dave Dixon
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Post by Dave Dixon » Thu Sep 04, 2008 7:56 am

SCA was really something! I'm not sure if it is still in use. I built a decoder from an article in Pop. Com (or whichever name it had at the time) to get a new SCA station I had heard about in our area. It was called PRN - Physicians Radio Network. Doctors were buying "special" receivers to pick up this network with information for "doctors only" during the beginning of the AIDs scare!!!! In the meantime I found out that one local station had two separate "musak" type stations on separate subcarriers. One was really mellow, while the other was somewhat more upbeat - if you can get away with ever calling musak upbeat! Just my two cents on part of the topic.

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Post by haklesup » Thu Sep 04, 2008 10:36 am

Various schemes were used to transmit digital and other video synch signals in the vertical retrace interval on NTSC or analog video. This was supposed to be hidden in the part of the picture that is above or below the screen but sometimes a misaligned TV or broadcaster would use more than the usual few lines to transmit the data so you would end up seeing it. I typically only ever saw it at the bottom but it was essentially the same thing.

As to exactly what that data was, you would need to determine the date and station you saw it on and call them yourself. There were some standards (like traffic, weather) but also some unusual schemes. I was aware of it at the time but never took advantage of any services.

In any case, with DTV/HDTV anything like that will be encoded in the data stream and not embedded the video information (unless there is something clandestine going on we don't know about). One could theoretically embed information in a DTV image decodable by the right equipment but I know of no such example.

European TVs have teletext, That data may have been transmitted this way, I'm not sure.

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Bob Scott
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Post by Bob Scott » Thu Sep 04, 2008 11:22 am

Miscellaneous digital information is inserted on lines 20 and 21 These two lines were normally the last two lines of the vertical blanking period. These signals are not normally visible. They occur during vertical retrace period(scans moving back towards the top of the screen as fast as the vertical oscillator's rise time).

On older and some cheaply made B&W sets without an additional vertical blanking circuit, these short white lines are visible during vertical retrace. I mean, These lines are supposed to be 7.5 IRE below black level as originally stipulated by the NTSC, but some engineer said "Most TVs now have internal blanking. Let's add some digital stuff".

Sometimes it's Time Code.
Sometimes it's an alert announcing a few seconds before a break in the program.
Sometimes it's digital internal communication to affiliates.
etc.

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Post by dacflyer » Fri Sep 05, 2008 4:46 am

veeery interestinggggg, thanks.

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Post by jwax » Sat Sep 06, 2008 4:33 am

I recall a "blinking square" in the top left that pulsed once per second for 30 seconds before staying on solid. It was a network signal to tell local stations of an impending commercial, so locals commercials knew when to cue in.
Yeah, some of us wanted to use that to switch the audio off for the impending commercial! :grin:

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Post by jollyrgr » Sat Sep 06, 2008 7:51 am

With a properly adjusted height, this data would not be seen as it would be hidden by the bezel around the screen. It is the data stream for Closed Caption and is on line 21 of the video. See the article at:

http://en.wikipedia.org/wiki/Closed_captioning
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!

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Post by Janitor Tzap » Sat Sep 06, 2008 7:58 pm

jwax wrote:I recall a "blinking square" in the top left that pulsed once per second for 30 seconds before staying on solid. It was a network signal to tell local stations of an impending commercial, so locals commercials knew when to cue in.
Yeah, some of us wanted to use that to switch the audio off for the impending commercial! :grin:
Hmm......

Interesting that you mention that.....
Sony had a VCR that cued in on that pulse to pause the VCR when Recording a program, to remove the commercials.
But, it never got over to the USA.
Because the Advertisers made a big stink about how people would not be seeing they're Ad's.
That version of VCR was quickly dropped.
The replacement VCR that SONY later came out with,
was the "Fast Forward Through Commercials" Unit.
A few other manufactures had this too.
But, the feature was later just simply dropped from later models.

As for the Data Stream buried at the Vertical Retrace Interval.
I'm still seeing it used for All the things everyone has mentioned.

Thou, the Pay Channels didn't last that long around here.
A lot of people at the time still owned old Tube Televisions.
By tweaking the tuner just right, you could get the channel in for awhile until the scrambling scheme changed.
But that didn't happen till after the show, or movie ended.
It must of given the Pay Channel Owners fit's to know that there wasn't
anything that they could do about it. :)


Signed: Janitor Tzap

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Post by jollyrgr » Tue Sep 09, 2008 8:36 pm

Janitor Tzap wrote: Thou, the Pay Channels didn't last that long around here.
A lot of people at the time still owned old Tube Televisions.
By tweaking the tuner just right, you could get the channel in for awhile until the scrambling scheme changed.
But that didn't happen till after the show, or movie ended.
It must of given the Pay Channel Owners fit's to know that there wasn't
anything that they could do about it. :)
Signed: Janitor Tzap
ON TV was an over the air subscription service back in the 1980s. Basically one "cable" channel with a set top box to tune it in. The signal was sent scrambled (suppressed sync) and the audio hid on a subcarrier. At the time I had an old black and white tube set; not hybrid, completely tube. This meant LOTS of controls to fiddle with. Sometimes with enough tweaking I could get a fairly stable picture. For sound it was much more interesting. I had a CB radio in my room with a magnet mount antenna on top. The CB was right next to the TV. Of course video "noise" from the TV would bleed into the CB signals. But I also discovered that on certain CB channels I could hear the audio for the scrambled TV signal. This was not perfect but it was good enough that I could follow what was going on with the TV show.
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!

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Bob Scott
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Post by Bob Scott » Sat Sep 13, 2008 12:40 pm

Janitor Tzap wrote:Thou, the Pay Channels didn't last that long around here.
A lot of people at the time still owned old Tube Televisions.
By tweaking the tuner just right, you could get the channel in for awhile until the scrambling scheme changed.
But that didn't happen till after the show, or movie ended.
It must of given the Pay Channel Owners fit's to know that there wasn't
anything that they could do about it. :)
Oh, Pay TV 25 years ago. Since that is a quarter of a century, and the statute of limitations is far less time, I can tell you a story:

Pay TV in my old home city was scrambled with a pulsing interfering carrier. Many hobbyists came up with various schemes to build notch fillters so they could get pay TV for nothing.

One just used about 4 feet of twin lead as a tuned stub across the 300 Ohm antenna terminals. The stub was tuned by a small piece of aluminum foil wrapped around the twin lead, and was tuned by sliding it up or down the outside of the insulated wire.

Another scheme used an air core coil of wire, mounted vertically inside an old tin tobacco can and soldered to the bottom of the grounded can. The capacitance of the coil to the can made a resonant circuit notch filter.

Another scheme was developed by a TV broadcast engineer at CBC. He etched a single turn coil on a piece of single sided 2" X 3" PCB. An adjustable ceramic trimmer cap was surface mounted in parallel with the "coil". Another 2" X 3" piece of single sided PCB was attached flat to the first PCB to act as a ground plane. There were two holes through each PCB on each end of the coil for two Female chassis RF connectors that held the PCBs together. A 250 Ohm trimmer pot was added to one side of the coil and helped to fine tune the filter. This notch filter tended to drift and tuning was critical.

I improved on the last method by making them out of double sided board. The back side was the ground plane. This eliminated most of the drift. I added small value fixed cap in parallel with a smaller value trimmer cap. This made fine tuning less critical.

Of course I had to boast about how good it was to my close friends, who immediately requested copies. Then they wanted more of them so they could hawk sell them in bars, so I started charging money. Basically, they got into the habit of selling these things to pay for their evening at the bar. Drinkin' for free!

Then a lawyer relative of mine wanted a couple for himself and a buddy so I honored the request. Now the lawyers want more, and one for a federal judge who heard about these thing through the grapevine and requested a copy. Gotta keep the lawyers happy!

So I went into mass production and dropped my price to wholesale. I mean, I don't want to retail these thing MYSELF! Too much risk! I bought and used up a thousand foot box of RG59 to make 2 foot jumpers c/w connectors. I bought several hundred lots of connectors, caps, trimmer pots and PCB by the 3' x 6' sheet until the supplier ran out of 1 oz copper PCB.

I'd organise my free time every day for a new batch.

Day 1: Cut board stock to size with a jig saw and guillotine paper cutter. Mask both sides with wide masking tape.

Day 2: Cut out circuit pattern on every board with an Exacto knife while etching loads of 5 boards in a GC Electronics bubble etching tank filled with ammonium persulphate. I won't use ferric chloride. It stains my clothes.

Day3: Drill and assemble/solder all the parts.

Day 4: Make hands sore by cutting and crimping 2' sections of RG59. Test and tweak on the rumpus room TV in the basement.

There was a newspaper article about the cable company trapping out channel 7 on whole streets because nobody was a pay customer. At that time, I made a decision to move to a better climate. The winters and summer biting insects prevented me from enjoying my speedboat.

Then one evening as I was tweaking a briefcase full of my new batch in the basement, I heard someone coming downstairs. I saw a dark blue uniform with a big silver badge on its chest appear. My subconcious panicked. I just about jumped out of my skin and my eyes near exploded. Then a loud voice said Hi! Where's the gas meter?

It just paid for my moving expenses to this city. I got a job right away at another TV station. 14 months later in November, the union struck and I was out on the street, getting warm by burning wood in a steel drum on the picket line. Luckily, while the strike was on, I got another job quickly and for more money....at the cable company's community access channel.

Of course that pay TV scheme didn't last. Looking back with hindsight, the cable company should have just shuffled the channel to a different one, but I guess that would have made their own "descramblers" useless too.

Do any of you have an old skeleton in YOUR closet?

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Post by Robert Reed » Sat Sep 13, 2008 3:48 pm

Bob
In our area the OTA pay TV which was superceded cable TV was established using a different scrambling method. They attenuated the horizontal sync pulse prior to modulation of the signal at the station, thus producing a very scrambled picture on non subscribers receivers. A group of us at the time came up with a novel Hor. Sync. restorer that had minimum invasion to the recevers circuitry. Then about a year later the station added video inversion to the transmitted signal. I went to work and designed a simple circuit to reinvert the video to its proper polarity. Unfortunately this required a bit of electronic skills to install in any given receiver, so it was not for everyone. Back to enjoying my "free" pay TV when not more than 6 mos. passed and they began to toggle those inversions about every 10 minutes.The solution here was a manual control as automating would have been too complicated. This cure required a 10 foot cord from TV to my easy chair and simple switch to keep in step with their toggling (i.e.-they toggle, I toggle). A few months later, their toggling changed to a rapid and random rate. At that point, I gave up as I couldn't keep up with it any longer. It was almost as if there had been a spy in our midst, reporting our actions to the station and them taking corresponding steps.
God, but I miss those "war games" as the veiwing wasn't important - it was the little victorys we scored.
P.S. The most memorable moment I had was in watching the Sugar Ray Leonard fight. Not only did I not pay for their service, but I did not have to pay the extra $10 just for the fight. All the paying customers had to shell this out if they chose to watch that match.

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