Tune in and Drop Out

so you see how a picture is recreated in a Cathode Ray Tube, but how does it get to your television set?

Television broadcasting is based on a signal, much like radio. However, a monochrome television signal is comprised of three pieces, and a colour signal is comprised of four.


The different pieces of a television signal are:

* Intensity Information
Intensity information is used to tell the television how bright or dark the phosphors need to be at a given point.
* Horizontal Retrace Signals
Horizontal retrace signals tell the television when it is time to move back to the left side of the screen after is has completed a line.
* Vertical Retrace Signals
Vertical retrace signals occur in the broadcast signal 60 times per second, and tell the television to move the beam back from the bottom-right side to the top-left side so it can paint a new image.
* Chrominance Signal
A Chrominance Signal is added to a monochrome signal to add colour to the image. Essentially, it is a separate frequency that tells the television how to modulate the electron beams so that they will produce the right colour combination for each pixel grouping. This part of the signal is ignored by old monochrome televisions.


So, if you take these four parts, add another frequency modulation for sound, and a vestigial sideband, and you have a full television signal. Your television takes in all that information, interprets it, and turns it into your favourite programs. Sounds like a lot of work, right?

Now think about that effort going into all those annoying commercials you see on television. Sheesh!

This is the basic principle behind image reception for televisions, and all the signals you receive basically operate in this same fashion, from using an antenna to pick up the Saturday night hockey game to receiving satellite broadcasts on your high-definition widescreen television set.