[opendtv] News: VHF: Now Everything You Know Is Wrong
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: OpenDTV Mail List <opendtv@xxxxxxxxxxxxx>
- Date: Sat, 27 Jun 2009 07:41:11 -0400
http://www.tvnewsday.com/articles/2009/06/26/daily.4/
JESSELL AT LARGE
VHF: Now Everything You Know Is Wrong
By Harry A. Jessell
TVNEWSDAY, Jun 26 2009, 3:23 PM ET
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.
To get a handle on just how much the digital transition has affected
conventional thinking about TV broadcasting, consider the FCC
national TV ownership cap, which is based in part on the now quaint
notion that UHF stations deliver half the coverage of VHF stations.
The rules put no limit on the number of stations any single company
may own. Instead, they say that it cannot own stations reaching any
more than 39 percent of the 114 million TV homes in the U.S.
In calculating reach, station groups may cut in half the homes
reached in markets where they have only a UHF station. For instance,
they would count only 3.7 million homes in New York, even though the
No. 1 market actually has 7.4 million.
This is not a problem that is going to go away.
Fixing VHF for regular broadcast viewers may simply be a matter of
getting them the right antenna, one that can make up for the
insufficient power and poor building penetration.
But the nearly 500 full-power stations with VHF channels may be
struck in a band that puts them at a severe disadvantage in making
the leap to mobile. It doesn't seem fair.
For the new FCC chairman, Julius Genachowski, who's expected to take
office next week, it's one more thing for him to worry about.
Harry A. Jessell is editor of TVNewsday.com. He can be contacted at
hajessell@xxxxxxxxxxxxxx
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