Okay, I get the gist of it, there's just a little part that I don't understand. My book says that modulation is the process of putting information onto a high frequency carrier for transmission. How exactly is this done? How are the signals combined?
2007-08-27 15:27:12 · 4 answers · asked by Galbadian 2 in Science & Mathematics ➔ Engineering
In current technology, AM signals are mixed with the carrier frequency and then amplified. This "mixing" is basically non-linear. The 2 signals are simply added to each other. At one time this mixing was done by using a transformer in the output line of the RF amplifier that was being operated in a class 'A' mode. The modulation signal was forced onto the un-modulated carrier wave by virtue of the transformer effect. The problems with this was efficiency, as well as the power needed from the audio source. For a 1000 watt transmitted signal, you needed 500 watts of audio power. The new methods of adding the carrier to the modulating signal means that less power is needed, and more efficient amplifiers can be used to increase the transmit signal strength.
FM modulation is done in the carrier generator itself. The carrier frequency is changed at the same rate as the modulating frequency. Basically, a variable capacitance diode is used to alter the frequency of the carrier with the modulating signal fed to the diode, which is connected in parallel to the oscillator.
2007-08-27 18:16:36 · answer #1 · answered by Anonymous · 0⤊ 0⤋
How exactly it is done depends on the type of modulation to be used. The carrier signal has three characteristics that can be varied: amplitude, frequency, and phase.
For amplitude modulation, the process mathematically appears like a multiplication, or often an addition and a multiplication together. So a circuit that acts as a multiplier could theoretically be used. But any non-linear element should work, such as a diode.
The mathematical constructs for frequency and phase modulation are more complex and so is the circuitry. However, simple circuits are also available. There are a number of good books available. But a web search on "modulation circuits" should reveal some also.
2007-08-27 22:42:48 · answer #2 · answered by joe_ska 3 · 0⤊ 1⤋
Signals are modulated by a process knowing as mixing. A mixer is used or basically a multiplier that allows the low frequency signal to ride on top of the high frequency signal.
The carrier signal is also known as the local oscillator...this signal is mixed with your message signal. Then they are amplified and transmitted. On the receiver end they are mixed with the local oscillator again to retrieve the message signal. That signal is then amplified for the output to recognize.
2007-08-27 22:31:54 · answer #3 · answered by Anonymous · 0⤊ 0⤋
Two common techniques are amplitude modulation (AM) and frequency modulation (FM). They do what the names sound like. With AM, the signal is multiplied by the modulating signal. With FM, the frequency is varied slightly.
2007-08-27 22:37:01 · answer #4 · answered by ancient_nerd 2 · 0⤊ 0⤋