- The selected RF signal is amplified and sent into a demodulator which separates the AM or FM carrier signal from the audio signal (subtracts the carrier signal out).
- The AF (audio Frequency) signal remaining is amplified and sent to a speaker.
- With a television, two signals are demodulated and one is sent to the speaker and the other to the display.
- The CRTC, and the American equivalent, regulate carrier frequencies and power outputs.
- In addition to radio and television bands, frequency bands have been assigned for cell phones, citizen bands, ship-to-shore radio, aircraft, police, military, amateur radio etc.
- Digital Signals (Signals now used)
- Digital signals are now used throughout North America, and there are some important differences to the analogue signals of the past.
- Normal sounds and pictures that we want to transmitt start as analogue signals. To transmitt them as a digital signal, they first have to be converted into digital format. This is done with an analogue-to-digital converter.
- Analogue signals can have a wide range of continuously changing values. When converted to a digital signal, this wide range of values needs to be converted to a limited number of discrete values. In fact, the numbers used are zero (0) and one (1).
- All mathematical numbers can be converted to a binary number.
EG. The mathematical number 12 in the binary system of numbers is 1100 where as the
number 9 would be 1001. The numbers from one to thirteen in the binary system are;
1, 10, 11, 100, 101, 110, 111, 1000, 1001, 1010, 1011, 1100, 1101. Hopefully you can
see the pattern.
- Therefore, all sounds (frequency, loudness etc.) , and all parts of a picture (location in the picture, color, brightness etc.), can be assigned a number value which can be written as a binary number.
- The advantage of the binary system of numbers is that there are only two numbers 0 and 1.
- Zeros and ones can be easily represented in electronic circuits as a switch. A zero would be an open switch, and a one would be a closed switch
- A single frequence of electromagnetic waves can also be used to represent ones and zeros. A zero would be the electromagnetic wave turned off, and a one means the electromagnetic wave is turned on.
- Therefore, the number 90 can be represented as an electromagnetic signal like this.