I know this isn't really radio related but it's similar to the other TV thread....

Are there any TV station engineers out there?

If so, I have a question for you.

Way back when, before cable and satellite delivery systems, and everything (or most everything) was off-the-air they used to put some coding at the bottom of the vertical blanking bar, you could see it if you turned the vertical hold control (remember those?) slightly and brought the picture down from the top.

Some of the coding that they used to put in there was if it was the TV program or if it was a commercial. I'm really stretching but I think I remember they would also put in there if it was a network program or local program.

After that long discourse, what I'm asking is; Does anyone know if they still do that.

I believe they use the vertical interval for closed captioning.

Really? I thought it was on another part of the tv signal. When Closed Captioning first surfaced, there were two competing (and incompatable) systems of doing the captioning and the CBS-backed system eventually lost out. Maybe this is where the CC for that system was. Anyway, I've no sure answer on this.

I was hoping that they still put some kind of identifier there that would indicate whether it was program or commercial.

I remember a long, long time ago in either Popular Electronics or Radio and Electronics they published an article with a circuit that would detect the commercial then mute the audio.

It was something you had to build and it was long enough ago that the TV's still had tubes in them.

I'd love to find something to automatically mute the commercials!

When you diddle the hold and allow yourself to see what you describe, you are looking at the top of the scan (the first lines) or the bottom lines depending which side of the black bar you refer to. These are inactive (no video) lines. They are used for various test signals and closed captioning on line 21 and 22.

NTSC (analog) has 486 active lines of video (out of 525 total lines) although SDTV (digital) has 480.

The terms 'underscan' and 'overscan' are used to describe the active video resolution for NTSC and PAL modes. Underscan means that the active video area appears in a rectangle centered on the screen with a black surrounding area. This ensures that the entire active video area always is displayed on all monitors. Overscan utilizes the entire possible video area for NTSC or PAL. However, most monitors or televisions will cause some of this video to be lost beyond the edges of the display, so the entire image will not be seen.

Consumer devices are set up using some overscan so you don't see the edges of the image and hence the data dancing up on the top lines. Broadcast monitors have an underscan switch to allow to see the edges for maintenance and set up. Also, in CRT lifetime, the ability to maintain the plate voltage will decrease (go soft) and become less able to draw cathode current causing the image to shrink, so manufacturers will set the overscan up so the image will still fill the screen as old age sets in. Eventually the image will noticeably shrink (if the flyback transformer doesn't crash first).

For an explanation of blanking and retrace, I've already got that typed up on my website. The big shift to digital presents a whole new litany of techbull reductions for me to write and publish.

I used to enjoy watching on "underscan" for boom operators sneaking their microphone into the shot just a tiny bit. They'd do that to find out how tight they could go before they were in the shot. It was figured that everyone at home was watching on overscan and wouldn't notice. I don't think booms are used as much these days.

Andy, Great Web site! I book marked it. I'll visit it often! Thanks.

"Some of the coding that they used to put in there was if it was the TV program or if it was a commercial. I'm really stretching but I think I remember they would also put in there if it was a network program or local program. "
No!!! People thought that. There is no reason to put that kind of code out. Why would we want to do that?
There are test signals in that area. Closed Captioning is there, as Andy mentioned. The signals vary depending on the network when a network program is on. However, there is no reason to put up there what kind of program it is or its source or if it were a commercial. The purpose of commercials was to have you watch them. Why would we tell your system it was a commercial so you could turn it off? Advertisers don't pay if people don't watch the commercials.
We didn't have servers in those days. All material was directly from individual tape machines, film projectors, slides, etc. We switched each element individually. The tape machine did not know whether it was playing a program or a commercial. The switcher didn't know or care, either. The projectors were the same. Some commercials were done entirely by a slide or sequence of slides. How would the camera or projector know what type of source it was? The MCR switcher (person) was too busy to fool around with some identifier switch/encoder for no reason.

Some may have experimented with it but generally, the answer to your question is no.

Some switchers were not all framed/gen-locked/synced and hence would cause a glitch when changing sources. Some of those early commercial killers were using that to determine when to start and stop. Same with some early decks. Some used other methods. They weren't always reliable.

Cable, on the other hand, stripped some of the vits and inserted their own information into them. That is one way the early cable systems would scramble/unscramble their video. They used combinations of inverted frames, no sync, reverse sync, too much sync, etc. They would put the info for each frame on one line. With some knowledge and a handful of parts, one could build a decoder to get around that. It was not sophistcated. All you needed to do was observe that line(s) and see what the picture was doing and put some timers, J-K's, some gates, video amp ic's on a little board and you could have free cable. That was some time ago and they don't do that anymore. It was something to do on a rainy day just to see if I could do it.

A couple of years ago, on Channel 32 (and 5, respectively) I remember seeing a "KWBP-TV PORTLAND" printed across the top VBI if you'd set the vert hold off a little, if that counts.

However, from what I have seen recently they don't seem to do that any more.

Inserting call letters into one of the unused video lines came about as a way of identifying uplinks. It is probably still required for all uplinks to have an identifier separate from active video being transmitted, but where they put it in the digital signal is unknown to me at this time. Probably the same region to preserve the overscan/underscan scenario. I think it used to be line 5, or, um, line 7.

This wasn't on an uplink, it was on channel 32! (I didn't have satellite at that time, so I wouldn't know if their satellite simulcast on Galaxy [I think] C-band had it or not.)

But I did know the OTA 32 had it......I might even have videotape somewhere with recorded material from that time....I would have to look.

Andy, wasn't there a time in the past when all local TV stations had to ID that way? I think I remember reading that somewhaer, but I may be mistaken.............

I realize it wasn't an uplink, but the source of the ID can be inserted in the chain at many points within the video network of the broadcast facility, and once it gets on the tape or is introduced into the program chain, it stays.

I don't know about what the current requirements, but I do know that shortly after Captain Midnight, all uplinks had to have their call sign encoded into the test signal lines of the video so that all signals illuminating satellites could be identified and located.

"Tech Firms Push to Use TV Airwaves for Internet"

http://www.washingtonpost.com/wp-dyn/content/article/2007/03/12/AR2007031201395. html

On one hand, I think this is a potent tech. Given we are not gonna be doing nearly as much with this spectrum, TV wise, as we could be, I'm ok with the Internet access.

On the other, it reeks of the larger corporations really wanting a chunk of spectrum that is regulated so they can deal with the 'freebies' found on the current spectrum.

There have been, and will continue to be, lots of battles about that. Maybe this will cool their jets some, leaving the wireless spectrum to people, more than corps.

I'm at odds with losing traditional broadcast television. I still think canning NTSC is a big mistake, but it's done and over it seems. I watch so little local television, maybe it's time for new things.

I'm curious about how backhaul is achieved. Up until this year satellite broadband delivery required a phone line for backhaul. Two companies are currently rolling out bidirectional satellite service, with every download user has an uplink capability for backhaul. If you use e.g., ch 2 for download, how do they propose to receive and manage the backhaul using another? VHF slot emanating from 1000's of points?

I'd guess some kind of spread-spectrum technology, allowing all of the backhaul links to be handled as a single "signal" by the sat and then seperated afterward once it gets back to the ground station.

Perhaps land line backhaul/uploading will be replaced with cellular technology, or something similar?

not likely... cellular bandwidth is just too precious/expensive. I know DirectWay at least sends it's backhaul right up to the bird somehow.

Maybe "spot beams" in reverse?

THis is interesting.

A system very similar to this (if only in idea, not necessarily in technology itself) was deployed by Microsoft, Intel (I believe) and PBS in the late 1990s, called "Wavetop" as part of PBS' National Datacast Service. (Some of you might remember this as a component of the "Webtv for Windows" software that shipped with Windows 98.)

Needless to say Wavetop had several severe tech limitations, being broadcast above the viewable picture area of a PBS television channel (hence its name) it had very limited bandwidth and was a one-way only system. (Supposedly with a modem connection, it *could* be used as a crude two-way system but I doubt if this was ever used a lot.)

It was able to pipe HTML content, pictures, TV listings and possibly short video clips directly to your computer through the TV tuner on a video card. Unfortuantely WT couldn't display the actual TV broadcast while it was running.

You could think of it as a sort-of "Directband-like" system for computers over TV airwaves/cable channels, instead of an SCA channel.

Ultimately WT had proven to be a total market flop and was discontinued several years ago.

(Did OPB ever have a Wavetop feed??)

For what it's worth, I have run across some VCRs that can automatically set their clocks using information broadcast by PBS stations.

I have two VCRs that can do that--my 2000 (?) Panasonic PV9662 and (very old) 1995 RCA VR652HF.

I can in fact confirm that OPB does indeed currently broadcast a time signal. (Not certain of code format--might be an IRIG-based coding or something like that.)

The Panasonic apparently has a function that can programme its VCR Plus system with a "channel map" supposedly also carried along PBS' datacasts. It also has support for a "TV-guide-like" EPG, supposedly also provided by PBS. I have tried setting these up a couple of times in the last year or so (just on a whim) but it doesn't appear channel 10 has these services any more.

I thought the auto clock feature through the local PBS outlet had been standardized into VCRs for years! All of mine have it and some are pretty cheap.

Actually, closed captioning (at least its technology) is a child of the time-sync service, though they gained public notice (and may also have been implemented) in opposite order.

The National Bureau of Standards (the WWV folks) researched distributing time signals via network TV, and called the development "TvTime." It was actually ABC-TV who made the initial inquiry into applying the technology to CC; a CC'd episode of "The Mod Squad" was broadcast as a demo in 1971.

(About this time the BBC was experimenting with CeeFax, predecessor of TeleText, which is similar but more complex than CC. This followed various GPO experiments in England and France in phone-based VDT info retrieval--in France, Minitel terminals were distributed to eliminate the cost of printing phone books. Somewhere along the line CC, known there as "subtitles," were incorporated into the Teletext system in Europe, and is therefore incompatible with our CC system.)

The Secretary of Commerce's petition to the FCC for CC service failed, but was noticed by PBS, who was experimenting with open-captioning from 1972 (first the French Chef, then ZOOM, then a captioned rebroadcast of ABC's evening news, etc.), and thereafter worked through WGBH's Caption Center with NIST (the NBS' new name them) to refine the system, which was approved in 1976 and became operational in 1980.

http://www.itl.nist.gov/iad/itaccess01/Presentations/KBRemarks.htm
http://interactive.wgbh.org/wgbh/pages/captioncenter/milestones.html
http://www.davehowe.com/#3._Television_Time
http://en.wikipedia.org/wiki/Ceefax

I can't find a year for TvTime's development but it appears to have been 1971.