When did B/W broadcasts stop?

[Steve D.]

Hey Pete,

I'm not so sure those old 50's color programs aren't still inside my CT-100 somewhere.
I remember the movie "Contact", where an Earth bound SETI scientist received tv images from the 1936 Berlin Olympics being returned to us from a distant galaxy. Fascinating stuff.


-Steve

[old_tv_nut]

OK, I couldn't resist:

photon energy = hf = 0.4136e-14 electron volts x f

supposing 500 MHz (about channel 19), hf = about 2e-12 ev

putting that into joules (so we can work in joules/second or watts):
photon energy = 3.3e-31 joules.
Then assuming 500 kW effective radiated power, to a receiver in the beam this looks like 5e5 joules/second or 1.5e36 photons/second into a full sphere.

Distance to nearest star, proxima centauri = 3.8e16 meters, so the sphere at that radius has an area of 1.8e34 meters.

To reconstruct the signal we need about 12 million samples per second, and each sample needs about 900 photons to get a 30:1 signal to noise ratio. (This assumes a photon-counting detector, and ignores thermal noise - a big assumption, but let's go with it.)
That means we need a total of 10.8e9 photons per second, so we need a dish of area
(1.8e34)(10.8e9/1.5e36)=130e6 square meters, or about 6.4 kilometers radius.

If we only want to detect the carrier with a 1 Hz bandwidth, we could get by with a one or two meter dish (really would use a more conventional UHF antenna).

This says that the signal does not get very far in galactic terms as a watchable program. It also says something about why space probes use digital signaling and error-correcting codes, so they do not have to reach the high signal to noise ratio needed for analog transmission.

[Sandy G]

Awww, shit ! Killjoy ! It's a LOT more fun to think somewhere out there some little green whatzit is laughing his asses-all 3 of 'em- off at "Milton Berle" or "I Love Lucy"...<grin>-Sandy G.

[Aussie Bloke]

I personally don't know when American B&W broadcasts stopped but I guess main networks like CBS and ABC would of went full colour by 1967-69 period. I read that NBC was in full colour for all programs by 1966 being the first all colour station, well it's obvious for NBC to be first to drop B&W broadcasts as it was first really give NTSC colour technology a fair go unlike the other networks !

In Australia, us being the LAST developed country to get colour television , between the beginning of colour broadcasts on 19th October 1974 to the opening day of colour 1st March 1975 B&W broadcasts gradually reduced and on 1st March 1975 (the opening day of colour) all networks went full colour for all TV shows except for older repeats! Though some commercials were still done in B&W right into 1976 a mate told me.

Cheers
Troy

[oldtvman]

for the most part after nbc crowned itself the full color network in 1966 everyone else followed suit even cbs

[nasadowsk]

Actually, doesn't NTSC still transmit the full B&W signal anyway? Color's just something added to the mix - you could say B&W broadcasting never stopped

[old_tv_nut]

Turn on the weather report, then turn the color control to zero, and note that there is no longer any great concern for distinguishing between chart colors on a B&W set, although they usually avoid using equal-luminance colors for titles/backgrounds. So, some of the practices of black-and-white broadcasts, like checking contrast on-camera, have disappeared.