|QAM or 8VSB for DIGITAL SIGNAGE?
HD LCD and Plasma televisions have been dropping in price dramatically
over the last few years. Digital television modulators are now also
available at reasonable prices.
By law, all digital televisions must have MPEG-2 decoders and both
8VSB and QAM demodulators.
The marriage of these technologies presents a wonderful opportunity
to create low cost digital signage systems to carry prerecorded
When faced with the decision as to which modulation to use it is
a relatively easy choice. QAM (64, 256) can carry 38 Mbps. and 8VSB
can carry 19.2 Mbps. This means that QAM can deliver two HD signals
to a TV set, whereas 8VSB can deliver only one. In a well designed
content lineup, one can modulate three 12.9 Mbps streams with QAM
but only 12.9 Mbps high definition stream with 8VSB. Basically one
can allocate the 38 or 19 Mbps any way between SD and HD streams.
Conclusion: For Digital Signage QAM Modulation provides better
bandwidth and thus offers better value!
Laszlo (Les) Zoltan, BSEE
Computer Modules, Inc.