Dielectric's John Schadler weighs in on VHF's practicality for mobile TV
May 4, 2010
Last year at the NAB Show, John Schadler,
Dielectric's director of advanced antenna systems development and SPX master inventor, told me that his next research project was determining the feasibility of mobile broadcast with VHF. True to his word, Schadler was on hand this year with new data on the question. His bottom line on the subject is that VHF "may not be practical" for small, handheld devices.
"Circular [antenna] polarization with VHF offers an improvement over horizontal polarization for a small, handheld device," Schadler said. "But the disadvantage is [an] inefficient (small) capture area. So you need more signal strength."
Schadler does the math. "You have 3.5db less variability in mobile signals with VHF than with UHF. But you have a -19.5db loss because of inefficiency: a -16.5db disadvantage," he said. That disadvantage means longer antennas. "The original cell phones had long, extensible antennas and nobody wanted them," he reminded me, adding that the laws of physics don't change with the fashion. "Our world is obsessed with miniaturization, but antennas are immune."
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