Wednesday, December 12, 2012

Genuine Safety Electronic :How do TV Antennas Work ? has great information for everyone:

some of us may already know the dish that captures the TV broadcast that we can enjoy this time, wanted to know how the system works, well, let's discuss in this post.

Satellite Signals

Satellite signals are beamed around us, at us and through us all the time. Look in the night sky on a clear night and you'll see several steadily moving pinpoints of light---sunlight reflected off non-geosynchronous satellites. Many more satellites hold stationary orbits and look, to us, like stars. C-band and Ku-band are measurements of the signal wavelength along the electromagnetic spectrum. To put it in perspective, red light is a long visible wavelength; infrared is longer, and microwaves are longer than that. Radio waves are longer than microwaves. C-band and Ku-band are microwaves of differing lengths. With all those signals of various types beaming down all the time, how does a satellite antenna catch the correct invisible low-level microwave signal?

Signal Comes In

Picture a signal beamed toward Earth from a geosynchronous satellite. Geosynchronous means that a satellite matches the Earth's rotation, so that from the ground, the satellite appears stationary. Television broadcast satellites are a good example of this, which is why once a TV satellite mini-dish is installed it does not move; the Ku-band signal arrives from a fixed point in the sky. Older model satellite TV dishes, called C-Band for the signals they were designed to catch, did need to rotate to catch signals from different satellites in order to change channels, but each of those satellites was geosynchronous.

Antenna Catches the Signal

Satellite antennas are dish-shaped for a specific purpose. The "dish" is a parabolic reflector. If you remember high school geometry, a parabola is formed when you toss a ball up and it comes back down. As long as the ball moves away from its point of origin (not straight up and down in the same line), the u-shaped flight path is a parabola. The parabolic reflector catches the signal when aimed correctly. The signal should be coming straight at the antenna. If you imagine an open umbrella, the handle would show the correct angle of the signal beaming toward the reflector. The incoming microwave signal bounces off the metal reflector. The parabola shape is important here because no matter where on the dish the signal strikes, it bounces off the dish to the same exact point.

Antenna Focuses the Signal

For prime-focus antennas (see Resources for other types of satellite antennas), the signal is focused at a point out in front of the dish reflector, again just like the handle on the umbrella. The satellite antenna will have a collection device at that exact point to catch the signal, called the "feedhorn." The feedhorn sends the collected signal to a low noise block (LNB) which translates the C-Band or Ku-band signal into L-band wavelengths, a signal the receiver will be able to further manipulate.

Signal is Transmitted to Translation Device

The LNB transfers the signal through cabling to the receiver, which translates the L-band signal into a television picture or computer image or sound, whatever the signal was at original upload. has great information for everyone: