Basketball Song Playlist 2010

AM (amplitude modulation) PROBE

you ever you wondered Why, the reason or circumstance that has only satellite radios for AM are cheaper than those receiving FM or both?

Well first let's see how the world is currently about radio receivers.

Beginning with the news that the AM band will soon be removed from the air (if you can call it that) as its transmission is expensive compared with the results of transmission and of listeners he has, after all who has not heard stations that listen to our grandparents and even our parents.

This music most of us do not like, but in the end, music is there and pass it to the few who listen,

We describe various phenomena occur with AM signals, actually it is produced, what we mean generation is far less expensive than FM, since it only requires a multiplier, or the two waves together in a single conductor, while in FM is needed gives a wave circuit variant frequency as the input voltage.

The real problem facing broadcasters against the transmission over the air, since for AM it requires higher power than FM, since it is being transmitted amplitudes and frequencies respectively. In FM, as the frequency changes are those that carry information, the amplitude can be smaller by reducing the transmission power.

you noticed that AM stations are heard best when it is night or in cold weather, this is because the scale is important and not the frequency, when cold, the air particles are closer together (this is a concept of heat expansion of gases), then the wave riding is better, ie it can pass without much trouble, this phenomenon is the solar radiation noise ( sunlight interference on the transmitted wave).

also mention, why not, the fact that the AM band can be heard beneath the bridges where the FM band can not be heard, since the amplitude is important in AM, as already mentioned, you can move walls, floors and ceilings with fewer problems than the FM, in the latter are reflections, wear and other circumstances that make little wave and disappeared.

Well, we could continue with the advantages and disadvantages, if we see it, a band over another, but that's not the question that concerns us, the problem with our attention is the price AM receptor, then begin:

In a radio, the equipment is in charge of making (creating) the AM wave will be transmitted via antennas outside the premises ( the building of the radio booth.) We then define several concepts:

1. Modulation Amplitude is controlled cause changes in the amplitude of a signal using a modulating properties to be transmitted over an analog channel from the transmitter to the receiver.
2. Size: The height of the signal.
   

3. Signal: Graphical representation of energy.
   

4. Carrier: The signal to be transmitted, which carries the information.
   

5. Modulating: generally constant signal amplitude and frequency.
   

6. Frequency: number of turns in a second signal.
   

7. Channel: Middle of transmission of a signal.
   

8. Analog: For each time value is a value in range, and all are different.
   

9. Information: The set of data to be transported from one place to another

After the AM signal is created and transmitted, what comes out of the antenna is something like the following:

The first figure is the transmit signal (carrier), the second is the modulating signal that we have defined, and third is the result of multiplying the two signals.

As you can see, the modulating signal has a specific range (high change) and their frequency is also well defined, the carrier signal (transmitted) is the one that has many variations in amplitude and frequency . An important fact is that in the result, it takes the form of the modulating carrier in addition to the wave acquires a kind of mirror that makes it reflect on the horizontal axis.

important thing to mention is that the amplitude of the carrier should be the same value of amplitude modulating the information full reach its destination. In addition to the modulating frequency should be the Mayos carrier frequency at least twice.

This is the basic principle that AM receivers are cheaper. There are two techniques (at least they are the most used) to receive AM: Detection and Sensing Recticifación Surround (Carrier), the latter the most hackneyed, the circuit to receive the signal by this technique is as follows:

The diagram shows schematically the action of each of the elements on the AM signal (input signal)

a) The diode is an element usually made of silicon material, which cuts the signal allowed to pass only the positive or negative signal depending on its position on the source (input), the position is in the figure is to let the positive side, the opposite would happen the negative.

b) The capacitor is another element that serves to store (save) energy (usually voltage) with every little half-wave of the modulator, which now has twice the amplitude of the signal be transmitted (carrier) rises, the capacitor is charged and keeps the maximum value of each half wave of the carrier.

c) resistance is a means to discharge the capacitor, we must remember that this is an element that depends on the time to download if you have no means of discharge and to store energy for a long time can have side effects.

d) Each time you get a half-wave to the capacitor, this is loaded with the last remaining peak of the wave came and starts downloaded, when it comes to another wave, loaded again and takes the maximum value (highest) of the wave came, and so on.

e) the end we obtain the carrier signal (which is transmitted from the broadcaster, the defect it has is a DC level (an energy step of separating the signal from the horizontal axis by a specific amount) which in this case numerically equal to the amplitude of the carrier signal.

f) The latter problem can be solved by placing a DC source circuit reversed at the end of the signal back to the horizontal axis, or we can hold this level for the amplification CD back of the received signal, since the gain is only increased levels of CD in the alternating signal.

In conclusion, since the circuit for envelope detection (carrier) are nothing expensive or difficult to obtain as channels for AM reception, resulting in cheaper devices.

Bibliography:

Enrique Herrera Pérez, Communications 1 Signal Modulation and Transmission, An introduction to theory modern electric communication. Limusa Noriega Editores, 2006. Pp. 149-180

Author:

Samuel Perez Cedillo