In my RF Technology columns in TV Technology, I’ve outlined some of the problems that I anticipated in connection with VHF DTV broadcasting, I was surprised at the large number of complaints about VHF reception after the June 12 analog shutdown. Stations moving from a pre-transition UHF channel to a post-transition VHF DTV channel appeared to be most affected. UHF-only outdoor antennas perform poorly at VHF, and indoor antenna reception turned out to be even more of a problem. Inefficient antennas, amplifiers with too much gain and interference from a wide range of household devices have created problems even in areas where strong signals were predicted.
Charlie Rhodes, in his articles in TV Technology, showed how FM stations could create interference not only to DTV stations operating on Channel 6, but also to higher VHF channels due to intermodulation and harmonics generated in receivers and antenna preamplifiers.
As a result, many VHF DTV stations have filed petitions to move to UHF channels. Others increased power or added circular polarization. The FCC granted several VHF stations authority to increase power. From the reports I’ve heard, both of these measures have helped, with circular polarization providing significant improvement.
DTV broadcasters with VHF channels considering expanding their services with mobile DTV are facing another problem--the laws of physics make it very difficult, if not impossible, to build an efficient VHF antenna inside a cell phone or smart phone. However, VHF mobile DTV service should work fine, perhaps even better than UHF, in reaching automobiles or other vehicles where larger external antennas can be used.
