## Monday, December 1, 2014

### Sky Wave and Space Wave Propagation and Modulation

Sky wave propagation

There are different ways of propagation in this sky wave propagation. The first possibility is to use a particular tower who can communicate with the help of a tower of a particular height.

This kind of the signals are released into the space are to be further communicated to a specific region. The distance up to with the signal can reach depend on the height of the tower as well as the radius of the earth which is of course a constant value.

Once if you know the distance up to where it can travel, taking the point of the tower as a reference and the distance is a radius we can draw a circle and that is the area up to where the signal can be reached.

If you know the number of the people existing in the given place per unit area which is also called as population density,we can calculate the total number of the people that can receive the signal with the help of this tower. This is simply done by multiplying the area with the population density.

We can use line of sight concept by using the two Towers as a part of a sky wave propagation. Here instead of one tower we will use two towers therefore we can increase the range of the signal communication significantly.

The concept is actually the same but just at the ending of the transmitting range of the one tower we are going to put another tower who is having a beginning of the receiving range. Thus we are able to cover the double area that what we have covered in the previous case therefore it is more reachable to people. The maximum possible distance between the two Towers shall be the sum of the distances up to where the first tower can send the signal and the second tower can receive the signal.

Problem and Solution One

Here we are going to solve small problem basing on the concept of the height of the tower  or  the transmitting antenna. When the distance up to where the signal has to be reached is given,we can calculate the corresponding requirement of the height of the tower as shown below.

Problem Two and Solution

Consider solving one more problem basing on the concept of the line of sight as shown below. In this problem we would like to calculate the height of the transmitting antenna as well as the receiving antenna when the maximum distance between the towers is given to you and the ratio of the heights of the towers is given as shown below.

There is a third possibility in the sky wave propagation that is by using the particular layer of the atmosphere that is there. Above the surface of the earth we have different layers.We can use ionosphere as a reference which can reflect a particular signal frequency. Of course this can do the job only for a particular frequency and once if that frequency range is crossed, the signal is going to overshoot the layer therefore it will never reach the destination and the receiving antenna.

Space wave communication

In this kind of communication we are going to depend on satellites rather than depending on the nature like ground and space. An artificial satellite is a man-made satellite that is being sent into the space for the particular needs and satisfactions of the communications and for some other purposes.Now a days we are having a satellites called as geostationary satellites.They always appear stationary from the surface of the earth. It is just because they have the time period similar to the  earth  that is 24 hours and rotating from west to east.

This kind of satellites will have dedicated transponders who can receive and send the signals of particular frequency ranges. Using a transmitting antenna on the ground and the receiving antenna in the devices we can use a satellites very effectively for a very nice communication.This is the most dependable communication kind of the system  as of now and are used very much widely for Telephonic  communications  like cell phone communications, Internet communications and the TV.

When you are sending the signal via the space wave communication there is one important issue that the signal itself is not good enough to travel for that much longer distance and come back via the satellite.We need to give enough strength for the signal to travel to this much long distances by adding extra career to that and the phenomenon of adding a career like this is called as modulation.

Technically there are different types of modulations like amplitude modulation, frequency modulation and phase modulation. In the case of the amplitude modulation we are going to add a particular signal who is having a higher amplitude to the massage signal, in the case of a frequency modulation we are going to add a high-frequency signal to pass the massage signal.  Phase modulation is a way of modulation such that will be passing the message from one place to another place by adding a specific phase.

At the input level,with the message signal this modulation signal is also attached with a device called modulator.This will add the required carrier signal to you the strength for communication and then further passed to a transmitting antenna. At the receiving level there will be another demodulator which can eliminate the carrier signal therefore the original message signal can be reached without any serious loss.

Amplitude modulation

The phenomenon of adding a higher amplitude to the original message signal as a carrier signal is called as a amplitude modulation. The impact of the message signal on the carrier signal is as shown below.The amplitude modulated signal will have a range of angular velocity as the sum and difference of the angular velocity of the message signal and the carrier signal as shown below.

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