TV Transmission: Old & New

Factual Questions
1

As I think about the change from conventional to high-density TV broadcasting, I wondered:
When TV shows changed from B&W to color, was it necessary to change the manner in which TV signals were broadcast? I guess I refer to the transmitter itself as it is being changed now to accomodate HDTV.

By asking this, I am admitting that I am not really sure how the color “aspect” is carried by the signal. Of course, I’m not really sure how HD is accomplished. I mean, heck, an EM wave only has so many characteristics! Well, to the layman, anyway, I guess…

2

High Definition TV, you mean. Television is dense enough already.

Then we’ll turn our tommy guns
on the screaming ravaged nuns
and the peoples voice will be the only sound.
-P. Sky

3

IIRC, the color signals had to be able to be interpreted by existing B/W sets. So the signals did change, but were constrained so that B/W sets would gray-scale the colors.

So even today, a TV set built in 1949 should still interpret today’s signals. How many other technologies have that staying power.

What would Brian Boitano do / If he was here right now /
He’d make a plan and he’d follow through / That’s what Brian Boitano would do.

4

HDTV’s have all sorts of display formats you can choose. Weird.

Shucks, who can afford one anyway? $7,000 for the cheapest one.

5

The TV transmitters themselves had to be changed to transmit color. As AWB said, the signal was (and is) such that a B&W TV only picked up the gray levels (as it always had).

The change from a B&W to color transmitter isn’t nearly as big as the change from color to HDTV.

Arjuna34

6

The system used by RCA to broadcast color was compatable with existing B&W set.

CBS came up with a technically superior color transmission system that actually got FCC approval, but it was incompatable with B&W. RCA convinced the FCC to rescind its approval and go with their system.

“What we have here is failure to communicate.” – Strother Martin, anticipating the Internet.

www.sff.net/people/rothman

7

if you are talking about the different formats, like the lines of resolution and how it scans (interlaced or progressive), you don’t chose them, the networks do (or station) technically you could have 3 or 4 of the signals that we’re used to (as far as resolution goes) broadcast over one HDTV signal

8

It could have been worse. We could have got stuck with Rube-Goldberg-vision, the color system from the forties that used a big spinning color wheel in front of the B&W screen!

“Smells like the TV’s burnt a bearing…”

I for one welcome our new insect overlords… - K. Brockman

9

Geez… This bugs me just a little bit… I don’t mean to pick you apart, but it seems to me any of our successful technologies qualify.

Radio, radar, sonar, automobiles, airplanes, helicopters, rockets… not to mention simpler “technologies” like brick and mortar, forged steel, carpentry, etc. (Hey, at some point, somebody was amazed by the great advance of hammer and nail…)

Weapons come to mind as well… Tanks, circa 1917; AK-47’s, IIRC were developed in 1947; H-bomb in 1949. I’ll leave it to the reader to decide whether they consider those “successful” though…

I know your point was that, “Wow, it still works,” but so do a lot of things. Just my $.02.

[/hijack]

10

It is my understanding that the CBS system was the colorwheel.

Note that we paid a price. Until the 70’s, color reception was generally crap, and due to the color signals having to be stuffed in between the gaps of the B&W signal. (It wouldn’t have worked at all, if the human eye/brain system didn’t automatically adjust the colors it sees to match the B&W it sees.) Eventually, tricks involving extra color signals and circuits that automatically adjusted the television so that everything almost flesh-colored came out flesh-colored cleaned it up, but it took decades. That’s why NTSC is traditionally said to stand for “Never Twice the Same Color”.

John W. Kennedy
“Compact is becoming contract; man only earns and pays.”
– Charles Williams

11

The CBS system did have a mechanical wheel, but I think it was behind the screen, not in front of it.

“What we have here is failure to communicate.” – Strother Martin, anticipating the Internet.

www.sff.net/people/rothman

12

ubermensch, I don’t remember all the specifics, but HDTV’s can do formats like wide screen, letterbox, black frame, you know things like that to fit in non-hdtv programs.

13

*AWB: So even today, a TV set built in 1949 should still interpret today’s signals. How many other technologies have that staying power.

**mrblue92:
Geez… This bugs me just a little bit… I don’t mean to pick you apart, but it seems to me any of our successful technologies qualify.

Radio, radar, sonar, automobiles, airplanes, helicopters, rockets… not to mention simpler “technologies” like brick and mortar, forged steel, carpentry, etc. (Hey, at some point, somebody was amazed by the great advance of hammer and nail…)**

Yeah, I guess I was a little too glib in my statement. I was thinking of things like computers (IBM PC, XT, AT, 286, 386, 486, Pentium I, II, and III all within 20 years), music recording (cylinders, phonographs, 16, 33, 45, 78 RPM albums, 8-track, cassette, CD, DVD), and video (broadcast, Beta, Laserdisk, VHS, DVD).

What would Brian Boitano do / If he was here right now /
He’d make a plan and he’d follow through / That’s what Brian Boitano would do.

14

To clarify the answer to the original post, the transmitters *did[/] have to be modified when color came along, at least part of them anyway. The big power amplifiers and the antenna itself didn’t.

That an old B&W TV can properly receive a color broadcast is due to the way the information is encoded. If you try to imagine the frequency spectrum around a TV carrier frequency, I’ll try to describe it. A B&W broadcast has the “luminosity” amplitude-modulated on the radio signal, meaning that as the luminosity is brighter, the radio signal is bigger. If you look at its frequency spectrum, this causes the single carrier freq to spread out around it, taking up more bandwidth. The parts of the spectrum farther from the carrier correspond to the sharper aspects of the picture. After you get 2 or 3 MHz away, the signal is much smaller there because the high-frequency components will always be smaller.

Now you want sound with that picture? They just AM-modulate the sound, and stick that 4.5 MHz above where the video is, so there it won’t interfere with the picture and vice-versa. Have you ever seen a picture with lots of sharp edges that cause the sound to get noisy? The reason is that the sharp edges go up in frequency to where the sound is supposed to sit.

This was the way it was before color. To add color to it, they decided to leave the luminosity as it was, but add color information (hue and saturation). These are both encoded on a separate signal, which is then placed 3.58 some-odd MHz above the video. The hue information is phase-modulated onto this extra signal, and the saturation is amplitude-modultated. The reason that an oddball frequency offset (3.58…) was used has again to do with the spectrum of the luminosity. The luminosity will be approximately a repeating signal, repeating at the line scan rate, because one line won’t usually be too different from the previous line. The spectrum of a repeating signal looks like a series of spikes in the frequency domain, with the spikes being spaced apart by the repeat rate. The color signal is made to sit between where two of these frequency spikes will be located, so that there will be the minimal interference. The color signal doesn’t have nearly the bandwidth that the luminosity does, but that’s OK because your eye can’t tell whether color is high-definition.

15

RealityChuck:

It did have to be something other than just the color wheel in front of the screen as that system was totally compatible with B&W. The only thing you needed to add to the signal was a timing pulse to keep the wheel in front of the TV screen in sync with the one spinning in front of the camera lens (essentially your TINT or HUE control).

I for one welcome our new insect overlords… - K. Brockman

16

Remember, CBS built its system from scratch and their goal from the beginning was to have full color. So the specifications were nothing like those RCA has used when it was developing B&W TV. The wheel was a part of it, but the broadcast methods were nothing like RCAs.

Remember, these were two companies that couldn’t agree on the speed at which a record would be played . . . :rolleyes:

“What we have here is failure to communicate.” – Strother Martin, anticipating the Internet.

www.sff.net/people/rothman

17

Just remember by 2008 none of your TVs now will be functionable. This HDTV thing is going to be a mess. They are still arguing over why the USA chose an HDTV system that is inferior to Europes (of course not everyone agrees)

Over on usenet they are saying the thing about our current HDTV broadcasts is that you either get it or you don’t. It doesn’t fade in and out like our tv does now if the signal goes weak. Once the signal gets weak it fades out.

Chicago TV was supposed to have been upgrade to all HDTV by now but it hasn’t (all top 10 markets are supposed to but NYC and CHI were given waivers as they have to cope with buildings)

They wanted to build a huge tv tower on the west side of the city but locals complained as the sight of the tall towers would hurt the atmosphere of the ghettos and slums over there

18

don’t want to get into how they did it but you can thank your lucky stars that the FCC back then was powerful enough to set the standard so that color and b&w would both work. If they hadn"t we would still be in the development of color.It definately helped to get color tv’s into American homes.
HDTV is a little scary in that it will be so expensive at first. Not everyone can afford this luxury. Also with HDTV comes manditory pay tv. :cool

19

This I doubt. Watch as the final “cutoff date” gets pushed back again and again, in recognition of the fact that HDTV sets are prohibitively expensive.

–It was recently discovered that research causes cancer in rats.

20

I think AWB was mainly referring to downward incompatibility in audio recording systems.

But, besides the CBS color-TV system, there was another poor attempt – Philco’s Apple System. During a pre-graduation industiral-coop semester and then again fresh out of undergrad engineering school (mid '50s), I worked on that system a little at the then Philco Corporation’s plant at C and Tioga Sts. in Philly. That system was also a Rube Goldberg scheme which registered accurately the picture pattern on a CRT screen having a set of three vertical primary-color stripes, by means of an IF-frequency feedback system from an aligned fourth set of screen stripes which produced electrical outputs as the electron beam crossed them. That system, having its feedback signals out there flapping in the breeze in front of the tube, was never able to be shielded suffiently from other signals from the same set or from other sources. The lab knew at the time I was there, that the thing could never go anywhere. . .but we had fun. :wink:

Ray (TV or not TV. . .or somewhere in between.)