VHF: Now Everything You Know Is Wrong

Every so often, when I was a kid, my mother would start vacuuming while my brothers and I were trying to watch TV. The picture would tear and roll, even though she was in another room in the house. "Mom, Mom, you're wrecking the TV and it's the best part," we'd scream. Unappreciated in her efforts to keep a home with six children, Mom ignored us. She had work to do and didn't even care if it was reruns of Gilligan's Island she was trashing.

I was reminded of this slice of life by all this talk about how VHF in digital isn't what it used to be in analog.

It turns out the vacuuming problem has a technical name: impulse noise. It does terrible things to VHF signals and the TV pictures they produce and comes not just from vacuums, but from other electrical appliances with motors, florescent lights, power lines, radios -- the whole shebang of man-made interference.

The impulse noise is all around us and probably much worse today than it was 40 or 45 years ago when I was dead serious about my TV viewing.

The impulse noise is killing digital VHF reception, particularly on channels 2- 6. Stations don't have enough power to overcome the noise and, in the on-off world of digital, too much noise and not enough signal means loss of service.

When the FCC handed out digital channels, it had to limit the power of VHF stations to prevent interference among stations in the more tightly packed digital broadcast band. VHF signals do propagate well and so are more likely to interfere if power is not reined in.

VHF stations have other problems that attenuate what power they do have. Because of the long wavelengths of VHF signals, they have trouble penetrating homes and apartment buildings. What's more, many committed over-the-air viewers were sold UHF-only TV antennas or all-band antennas with small, lousy VHF elements.

It all explains why viewers are calling hotlines wondering what happened to their favorite stations and why broadcasters are looking for solutions.

Stations that have experienced significant loss of viewership since the switch to digital-only broadcasting on a VHF channel have been running to the FCC for help. Some want more power; others want to move back to their old temporary UHF assignment or find a permanent home in the UHF band.

Since the June 12 analog cut off, the FCC has granted extra power to three VHF stations (ABC's WPVI Philadelphia; Schurz's KWCH Hutchison-Wichita, Kan.; and Sunbeam's WSVN Miami) and has received requests from 11 others.

Post-Newsweek, for instance, asked the FCC two days ago if it could kick up the power of WPLG, ch. 10 in Miami, from 22 kW to 60 kW, assuring the FCC that it would not interfere with any other station.

The FCC also says that it has granted several requests from stations to retreat to their pre-transition UHF channels.

I heard the tale of one broadcaster with a major market duopoly who intends to ask the FCC if it can switch the stations' channels so that its Big Four affiliate would be on a UHF channel and its netlet affiliate would be on the VHF assignment.

The VHF problem turns everything I know about RF TV reception (and it isn't much) on its head. For the past 30 years covering the TV business, I had presumed that VHF was better than UHF. It gave you the same coverage for a fraction of the power of UHF and those long radio waves could reach farther.

I also recall that in the olden days UHF stations were harder to tune in. You clicked the dial to the VHF channel, but you had to tune in the UHF stations on a continuous dial as you would an AM or FM station on the radio. For whatever reason, UHF reception was always lousier.

Now, it seems UHF is the place to be -- and not only for regular broadcast service.

From what I'm hearing from RF engineers who are obsessed with this issue right now, VHF is going to have big trouble in mobile DTV, which is being hyped as the second coming of TV broadcasting.

"There is not an engineer -- a sane engineer -- who would disagree with that," says Sinclair's Mark Aitken, a member of the technical advisory committee of the Open Mobile Video Coalition. "VHF is not king in the mobile world."

According to Aitken and others, the problem is a function not just of power, but of wavelength. The tiny antennas being squeezed into cell phone and other mobile devices will have a tough time capturing VHF signals with their long wavelengths. The shorter waves of UHF are far more compatible.

"VHF mobile is going to be a real stretch," says William Meintel, a consulting engineer at Meintel, Sgrignoli & Wallace.