Differences in Analog & Digital TV Signal Frequencies

Written by jeff mcdonald
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Differences in Analog & Digital TV Signal Frequencies
Most televisions today have a built-in antenna to receive digital signals. (Plasma panel image by Nikolay Okhitin from Fotolia.com)

The differences between analogue and digital television are many. It's easy to become overwhelmed when trying to wade through the facts regarding digital and analogue television and the differences between the two. Analogue and digital signal transmissions are actually very similar. Digital signals initially were broadcast on higher frequencies when digital and analogue television both were being broadcast. The major difference now is the way channels are displayed.

Transmission Overview

Analogue and digital television signals are transmitted in megahertz (MHz). This is the same way that radio signals are transmitted. For TV there are three bands -- low VHF, high VHF and UHF -- each with its own MHz range. Low VHF covers the range between 54 and 88MHz; high VHF is from 150.8 to 174MHz; and UHF is between 470 and 890MHz. When digital channels were introduced, they used the UHF frequencies, while analogue signals were broadcast in the low VHF and high VHF ranges. Now that all television signals are digital, many broadcasters have reverted to their low VHF and high VHF frequencies.

Channels Display

One difference between analogue and digital television channels is how they are displayed on a TV. If you are a cable or satellite subscriber, your channels are listed by numbers designated by the service provider. If you use an antenna to receive television signals, there will be a difference in the way your television displays channels compared with when analogue channels were broadcast. Analogue channels were displayed as 2, 3, 4, 5, etc. Digital channels are displayed as 2.1, 2.2, 4.1, 7.1, etc. Digital broadcasters are allowed to divide their channels into sub-channels, since only one channel can be transmitted on a single frequency. Each sub-channel carries a different signal from the same broadcaster, a process known as multicasting. Broadcasters use multicasting to provide different content or to transmit standard-definition and high-definition broadcasts of the same show.

Digital Channel Examples

These examples of digital channels will use the Buffalo, N.Y. area's programming to demonstrate how digital broadcasters multicast using sub-channels. Channel 2 is made up of three sub-channels -- Channels 2.1, 2.2 and 2.3 -- that broadcast different programs. Channel 2.1 is NBC, 2.2 is Universal Sports and 2.3 is the Retro Television Network. Channel 17 also comprises three sub-channels -- Channels 17.1, 17.2 and 17.3 -- that use both methods of multicasting. Channel 17.1 and 17.2 are the high- and standard-definition broadcasts of PBS, while Channel 17.3 is Think, the Public Broadcasting Association's children's channel.

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