Tag: television

How does the picture get to the TV itself? How does a radio wave make a picture?

Lou Bloomfield Leave a comment

How does the picture get to the TV itself? How does a radio wave make a picture?

The television can reconstruct an image from a series of brightness measurements. It takes these brightness measurement and uses them to control the electron beam as it sweeps across the screen of the picture tube. It paints the picture one dot at a time and then starts over when it has finished. Thus all that the radio wave has to send to the television is a series of brightness measurements and some synchronization information (when to start a horizontal scan and when to start a vertical scan). It uses an AM technique to send the brightness measurements on a radio wave. The transmitter’s power varies up and down to indicate brightness just as an AM radio transmitter’s power varies up and down to indicate which way to push the speaker cone.

How does the picture tube know where to push the electrons onto the right areas/…

Lou Bloomfield Leave a comment

How does the picture tube know where to push the electrons onto the right areas/dots?

The television and picture tube simply scans the electron beam across the screen, one horizontal row after the next as it moves “slowly” down the screen. When it gets to the bottom of the screen, the picture tube brings the beam back to the top of the screen and starts over again. While the TV is scanning the beam across the set, it uses the signal from the television station to control the intensity of the electron beam and those the brightness of the spots on the screen. It also watches for sync information to know when to begin new horizontal lines and vertical sweeps.

How does the television camera record the picture?

Lou Bloomfield Leave a comment

How does the television camera record the picture?

Like the television picture tube, the camera generates a signal that indicates the brightnesses of individual spots one at a time. It first measures the brightness of light reaching it from the upper left hand spot, then the spot to its immediate right and so on horizontally across the field of view. It then moves down to a low horizontal line and repeats this sweep. It eventually records the light levels from the entire scene in front of it and begins again. It detects this light using an optical system that forms an image of the scene on a light sensitive surface. This surface may be part of an imaging vacuum tube (sort of a reverse picture tube), or it may be a semiconductor device that resembles a vast array of tiny photocells.

If black is a high current from the television’s radio receiver and white is a l…

Lou Bloomfield Leave a comment

If black is a high current from the television’s radio receiver and white is a low current, why do you get a bright spot when you increase the flow of electrons at that instant. Isn’t white a bright spot?

Yes, white is created by a strong flow of electrons. There are two separate circuits here. The current from the receiver section of the television isn’t what is sent through the electron gun. Instead, that current controls the electron gun. When a large current arrives at the electron gun (actually the grid) from the receiver, the flow of electrons toward the screen is pinched off and a dark spot is created. When a small current arrives from the receiver, the electron beam remains intense and a bright spot is created.