The Magic of TV – How Signals are Transmitted

Before you can understand how TV signals are transmitted and received, you need to know the different systems used. Each system transmits signals in a different way.


Cable Television


Television programs are uploaded to satellites circling the planet. The channels compiled are sent to the satellite dish of the cable company. The data is broadcast along with channels that are local. The data is transmitted in compressed format to the cable subscribers. This is done via coaxial and fiber optic cables.


Satellite Television


Satellite TV works this way: satellites beam programming at a height of over 22,000 miles. These machines orbit at 0 degrees latitude. If you can see these satellites, they will appear to be standing still. It is this near-stationary movement that makes it possible for a dish to lock in on it. Adjustments to the satellite are made so it can receive the Ka, Ku and C radio bands. The data is converted to video and audio.


Antenna (over the air)


The antennas used by local TV stations work via over-the-air digital radio signals. These are transmitted from the station’s transmitter towers. The information is received by your antenna. The antenna sends the signal to the cable where it is decoded. The signal is sent to your TV directly or a HD TV receiver box. Digital TVs have replaced analog as the standard across America.


What are Television Transmission Bands?


Bands / frequencies are used for transmission. Bands III to V are used in the US. The UHF and VHF signals are included here. Band I has the smallest bandwidth. Band II in the US transmits FM radio. It is optimized for audio signals; putting video on it will result in quality degradation.


Standard TV sets use bands III, IV, or V. These bandwidths have to carry video and audio. The video portions of television signals have 4MHz of video bandwidth. For audio it is 2 MHz, making for a total of 6 MHz. Every television channel has 6 MHz as per the FCC allocation. The lineup is as follows:


Band V – Channels 14 to 83 (470 to 890 MHz)

Band IV – Channels 7 to 13 (174-216 MHz)

Band III – Channels 2 to 6 (54 to 88 MHz)


UHF, VHF and Higher Bands


VHFs (very high frequencies) channels typically have the 2 to 13 channels. Channels 14 to 83 are in the UHFs (ultra high frequencies) level. UHF and VHF are very popular because of their extensive range. Bands at higher frequencies are less like radio waves and more akin to light waves. Satellite signals can use these frequencies but special utilities are needed.


NTC Standards


The National Television Standards Committee (NTC) is the regulatory body governing television signals in America. NTC specifications state that the resolutions for video lines have to be 525 lines and 3.58 MHz chroma carrier. The cycle has to be 60 per second.


The specifications also state frame displays have to be 30 fps. These standards were developed so television sets will have no trouble receiving signals. Note that these standards are for analog television signals.


While it is fairly easy to learn how TVBoman Rustom Irani signals are transmitted and received, the standards are more complicated. There are four digital television terrestrial broadcasting standards (DTTB). They are Digital Terrestrial Multimedia Broadcasting (DTMB), Terrestrial Integrated Services Digital Broadcasting (ISDB-T), Digital Video Broadcasting-Terrestrial (DVB-T) and Advanced Television System Committee (ATSC). This means a universal standard is unlikely.


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