Functional Block Diagram - Blonder Tongue Laboratories Inc.

Broadband Specification Guide
Digital Off-Air (8VSB) Reception - Digital Viewing (8VSB)
Functionality
This system will allow you to receive the local, digital (8VSB) off-air broadcast programming that is available
in the market and distribute it through the facility in it’s original digital format. This signal can now be handed
off to a traditional coaxial distribution network or a hybrid fiber/coax distribution network within the facility.
A digital television with an 8VSB tuner is required to display this channel. The main component difference
between a digital and standard analog channel in the headend is the channel processor. Because of signal
format differences, the digital signal requires a digital channel processor that is specifically designed for digital
off-air broadcasts. It is important to note that standard analog channel processors will not work on digital
channels and standard television sets will not receive digitally transmitted programs.
In Depth Discussion
Antennas are selected based on the frequency/channel that is to be received, not the content, all off-air/
broadcast antennas will receive both analog and digital signals, however receiving the new digital off-air
channel may require a new antenna because of the new channel frequency assignment of the digital channel.
Since the necessity of a pre-amp cannot be determined until a site survey is performed, it is advisable to specify
one “as required by site survey”. The pre-amplifier is mounted outside on the antenna mast, and requires
a separate power supply that is mounted in the building. The appropriate power supply for the preamplifier
being used must be specified separately. The digital processor is the system component that filters and
amplifies to condition the particular channel being received. The processor can convert the received channel
to another channel for output onto the system. It is common practice to convert desired local UHF channels
to non-broadcast VHF channels in the market. This is done to minimize losses, and make it easier to construct
and manage the distribution network. When the new channel is combined with other channels in the facility
it must be done at the correct level so that the signals do not interfere with each other. Digitally modulated
carriers (ATSC, 8VSB, QAM) should have an output signal level that is about 10 dB less than it’s equivalent
analog channel. Selecting one product from each category on the following page will insure you will have all
the necessary components for a working system. Once all of the products are identified, the specifications can
be looked up in the specification library at the end of this publication.
IMPORTANT NOTE:
The Federal government has set February 17, 2009 as the digital cut-off date. This means the current
simulcasting of both analog and digital HDTV/SDTV broadcasts will end and only digital broadcasts will
be available over the air.
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