8VSB Broadcast TV System

Since the start of Television in the late 1920’s the consumer has selected the channel to view by selecting a number on the TV such as channels 2 to 13 for VHF and 14 to 69 for UHF. With the advent of cable TV this has changed somewhat with channel options from 2 to about 125. The average consumer has become very comfortable with this system.

When the industry began development of digital TV and compression they had to develop a new system. The standard that was developed was established by the Advanced Television Standards Committee (ATSC).

For broadcast television the ATSC committee selected a broadcast modulation standard called 8VSB. Quite often this gets called ATSC which is incorrect as the ATSC standard is also part of the Satellite modulation standard “QPSK” and the cable standard “QAM”.

Because digital compressed TV is now capable of transmitting more than one program on a TV channel it was decided to give the program a Major channel number and a Minor channel number separated by a period (.) For instance a digital program that is carried on VHF channel 6 would be called 6.1. If there was a second or third program being transmitted they would be called 6.2 or 6.3. If they were transmitted on a UHF channel they would be 45.1, 45.3 and 45.7.

As the industry transitioned to Digital broadcast many broadcasters had to move to a UHF frequency. For instance Channel 3 in Philadelphia transmitted their old analog signal on channel 3. When they went digital they moved there service to UHF channel 26 yet they still call themselves channel 3, Very confusing indeed.

This means that if you put a antenna up and tuned your TV to channel 3 you will get no reception but if you tuned it to channel 26 it will receive the signal but labeled as channel 3. This is extremely important if you are using a meter to test for signal reception. A digital TV will automatically scan and set itself up but a meter is tuned manually so you need to know where to look in the channel spectrum for the channel you need. This link to the government digital TV broadcast web site can help http://transition.fcc.gov/mb/engineering/dtvmaps/

TV Antennas

The type of antenna needed at a specific location depends on geographic location and other factors, such as the presence of nearby structures etc.

Check the signal strength of local stations in a geographical area:

· Enter Location using address, zip code, city, state – Click GO

· A map of the entered location and a list of available digital TV signals will be displayed.

Tip – If the tool doesn’t put the marker in the right place, click and drag it to correct it.

· The digital TV signals are color coded by signal strength

Clicking on the call sign for a station will place the station’s transmitter location on the map, provide information about its signal strength at the entered location, and provide the RF (“radio frequency”) channel used for the digital transmission.

Click on the call sign for all stations of interest in order to map the full range of transmitter locations that the antenna would need to cover. This will help to determine whether a directional or omni-directional antenna is appropriate, and whether an antenna rotor might be needed.

Determining the signal strength of the weakest signal will help to determine the minimum receiving antenna capability (including, possibly, an amplifier) that might be needed.

The list of RF channels will assist in determining whether an antenna with both UHF and VHF capability is needed.