[opendtv] House Commerce Committee Probes DTV Transition
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 14 Nov 2008 16:01:49 -0500
Would be nice for those DTV stations moving back to their VHF channels,
but at much lower power than their analog VHF is currently using, to do
a short term test. To me, the plan for the DTV transmitter to go back to
VHF, at power levels that are 13 to 18 dB below that of the analog
transmitter, is a *far* more likely way to lose coverage area, compared
with staying UHF and going up to 1 MW ERP.
I also think that relying on the SFN idea is a losing proposition if
your goal is to increase coverage *area*. If you want to allow reception
in the entire market area, with ATSC or DVB-T, it's not practical to
space the transmitters of the SFN very far apart. That would create
zones where reception becomes difficult, probably only possible with
very directional receive antennas. Seems to me that whether you're
talking true SFN or low power gap fillers, the further you go to the
edges of coverage the less effective these multiple on-channel
transmitters become. *If* you are after coverage without gaps.
Doug Lung says:
"While the FCC may have underestimated the impact of white space devices
on cable and off-air TV reception, they have adopted rules for the use
of distributed transmission systems."
I'd restate that to say, "Just as the FCC has underestimated the impact
of WSDs on OTA reception, the FCC is overestimating the increase of
coverage area that an on-channel DTS configuration is likely to offer."
However, in their defense, the FCC did also mention translators as part
of this DTS idea.
Bert
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http://www.tvtechnology.com/article/69160
House Commerce Committee Probes DTV Transition
by Doug Lung, 11.14.2008
Many viewers of Wilmington, N.C., TV stations found that even with a DTV
converter box, they were unable to receive some stations' programming
when analog broadcasting was shut down in that market on Sept. 8.
NBC affiliate WECT moved its Channel 44 UHF DTV antenna closer to
Wilmington to provide better coverage for its community of license, but
was unable to deliver a satisfactory DTV signal over the rural areas
previously served by its Channel 6 analog transmitter.
Except for a few markets where transmitting antennas are located on high
mountains, it's impossible to cover the same area on UHF DTV as was
covered on analog VHF with one antenna. People will watch a weak and
noisy analog signal, but with DTV that's not an option. As the DTV
signal drops below the noise limited threshold of the tuner the picture
will fill with artifacts or disappear completely.
The problem is not limited to Wilmington RF Report has discussed and
linked to articles describing DTV reception difficulties several times.
Last Friday, the House Committee on Energy and Commerce looked at this
and other lessons learned from the Wilmington analog shutdown.
"The Wilmington test identified many problems related to the DTV
transition, including matters concerning rescanning analog-to-digital
converter boxes, adjusting or acquiring antennas and changes in the
areas where stations' signals are available," committee Chairman John
Dingell, D-Mich., and Ed. Markey, D-Mass., chairman of the
Telecommunications and Internet Subcommittee, said in letters to the
major broadcast networks and affiliate organizations, NAB, the National
Telecommunications and Information Administration and the FCC. They also
asked each stakeholder what steps it will take to avoid similar problems
on Feb. 17, 2009.
The letters to the broadcasters asked stations with DTV coverage areas
smaller than their analog coverage areas what they intend to do to alert
fringe analog area viewers to the post-transition signal loss situation.
The letters also asked what steps were being taken to make viewers aware
that antenna reorientation or new antennas will be needed to continue
receiving TV.
The problem is most serious for low-band VHF stations (Channels 2
through 6) that are moving to UHF channels that depend on tower height,
rather than mountain height, for coverage. In some markets, such as
Washington, D.C., increased tower height may not be an option.
Some years ago in my RF Technology column, I addressed the channel
congestion in the northeast United States. Squeezing all of the stations
into the core spectrum (essentially those operating on channels 7-51)
would increase interference, making it difficult for some large market
stations to up their power to match their low-band VHF coverage without
causing excessive interference to stations in adjacent markets.
While the House Commerce Committee letters did discuss antenna issues,
they did not specifically refer to what I expect to be one of the
biggest problems on Feb. 18-the loss of stations vacating UHF channels
and returning to their former VHF analog channels. In many markets,
including New York and Los Angeles, all DTV stations have been
broadcasting on UHF and many viewers installing antennas for DTV
reception have purchased UHF-only models.
The analog "soft shutdowns" being conducted in many markets will help
viewers identify problems with DTV reception, only to the extent that
the stations remain on their current channel or, at least, stay in the
same band on Feb. 18.
However, the news isn't all bad for UHF DTV stations migrating to VHF
channels. While viewers closer to the transmitter may lose indoor
reception, more distant viewers with outdoor VHF antennas may find they
can receive a reliable DTV signal from the station's VHF channel when
they couldn't receive it on UHF.
While the FCC may have underestimated the impact of white space devices
on cable and off-air TV reception, they have adopted rules for the use
of distributed transmission systems. Although this may not be a
practical solution to reach everyone predicted to lose TV reception on
Feb. 18, it does provide a way to reach heavily populated areas outside
DTV service contours.
There's one other bit of good news. On a trip to the East Coast in
October, I found I was able to get UHF DTV reception in Hagerstown, Md.,
of some Washington, D.C., analog VHF stations, with far better picture
quality (low-band VHF analog was barely watchable), even though I was
outside the predicted noise-limited DTV coverage contour. Fortunately,
interference was not a problem. For the checks I used an Artec T19ARD
USB receiver, an Artec AN-2A amplified indoor "post card" antenna in a
third-floor room and with an outdoor antenna and preamp 30 feet up in a
residential neighborhood.
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