| Video Noise February 2003
Infrastructure and
Digital/High-Definition TV
There are technical issues to consider when moving into the
digital-TV and high-definition-TV era. Obviously, equipment is the thing people think of
first. But you also have to consider small details like the cables you use to connect
everything. Your S-video cables are not going to be useful for HDTV connections, for
example. Your old VCR won’t record HDTV, and the new D-VHS recorders will record HDTV
only if you very carefully select the source/tuner. There are lots of details to keep you
busy doing research. And if you do your homework, then blink too many times before making
your move, the entire playing field changes and all your research will have to be done
again. There is a lot of change going on in the digital TV and HDTV arena, and it will
continue for years before things settle into something more stable and predictable.
There’s a detail that’s right inside your house
that you may overlook, causing all sorts of unexplained headaches when you make the move
to digital. It’s your "infrastructure" -- in this case, all the cabling,
signal splitting, and other signal distribution inside your home. Adding services,
primarily digital TV and HDTV, raises the bandwidth of the incoming signal. Parts of your
infrastructure may not be capable of handling the higher frequencies. To get glitch-free
digital distribution you may very well need to change some elements of your
infrastructure.
 Standard-definition cable TV (analog
channels) and broadcast TV antenna-distribution systems typically have a bandwidth
(frequency range) of 500,000,000Hz to 600,000,000Hz (500MHz to 600MHz). These systems
typically use RG59 coaxial cable to carry these frequencies. The RG59 cable is usually
terminated with metal F-connectors. The F-connectors are crimped into the shield of the
cable, and the center conductor of the cable forms a "stinger" that penetrates a
small hole in the middle of the mating connector. The F-connector is threaded internally
and the mating connector has external threads. You shouldn't ignore the screw-on/off
F-connector's role in your transition to higher frequencies for digital signals, including
HDTV.
New digital signals including HD can extend up to
950,000,000Hz (950MHz is almost equal to 1GHz). There is good news and bad news in this.
The good news is that the RG59 coax cable that is probably in your walls, attic, basement,
or crawl space is perfectly fine for carrying signals with frequencies that high. The only
problems that might affect the cable would result from physical damage, like cuts that
penetrate the shield. A cut in the cable may not be a problem at lower frequencies, but at
higher frequencies you could have a significant signal loss. The bad news is that the
older F-connectors on the ends of the existing RG59 coax may not be performing especially
well at frequencies approaching 1GHz. There are new F-connectors on the market that deal
with higher frequencies quite well. The new F-connectors are identified by their longer
body, the special compression tool used to install them, and their rating for use up to
1GHz or higher. You cannot use the same old crimping tool you may have used with older
F-connectors though; you need to use the new compression tool with these new
F-connectors.
If a distribution system is feeding a number of outlets in
your home, it may not be designed for operation at higher frequencies approaching 1GHz.
Distribution systems can be as simple as signal splitters that sell for $1 to $8, or as
complex as a video-amplification and distribution system that has four to twelve amplified
outputs and can distribute video from a number of sources (DVD, satellite, etc.) to any
room in the house.
Signal splitters almost always have their operating
frequency range marked on the label. If the high number is 500MHz to 600MHz, the signal
splitter(s) will have to be replaced. Your choices for replacements are 1GHz splitters
that cost a bit more than their lower-frequency predecessors, or fancier videophile
splitters. Monster Cable makes the most readily available fancy models that have a
bandwidth of 2GHz and are gold plated. You’ll pay $15 to $40 for these splitters. My
experience with the Monster Cable 2GHz splitters is that they are definitely worth the
expense for rooms where video quality is important. I use one of their four-way splitters
in the basement to feed each room that has a TV, and use a two-way splitter in the
home-theater room to allow the use of the PIP function in that TV.
Video amplifiers and video-distribution switchers have a
bandwidth limitation just like signal splitters. If that gear doesn’t have a high
enough operating frequency, you will suffer significant signal losses at higher
frequencies. The signal losses will show up most often as momentary pixelization of
digital images. This could affect small areas of the picture or the entire screen. In HD
signals, you may experience loss of lock on the Dolby Digital audio signal causing periods
of silence. In severe cases, you may lose a digital or HD channel completely.
If you use cable TV as a source, you may have one of their
new DVR (digital video recorder) boxes that work like TiVo or Replay TV. These record
digitally onto an internal hard disk using a flexible menu system to allow automatic
recording of shows you want. They are then available to you at any time. These devices
also let you "pause" live TV and do instant replays if somebody does or says
something you missed. The DVR devices receive their programming directly from the cable
connection. If your infrastructure can’t deliver the full 950MHz bandwidth, you can
have all sorts of problems with the DVR. It may record shows you didn’t request, drop
shows you did want recorded, and fail to accept new shows into the scheduled recording
list.
How do you get your infrastructure tested and updated? To
know for sure whether you're receiving the maximum bandwidth, you need a professional.
They have equipment that will test the line, measure the signal strength across the full
bandwidth, and tell you without question whether the existing infrastructure is up to the
job. If updates are needed, they can pinpoint the problem areas and install new connectors
or recommend which components need changing to higher-bandwidth devices. If you decide to
add digital cable, HD cable, digital satellite, or HD satellite equipment, use their
installer. The installer will test the existing cabling and look at the splitters and
amplifiers. If he tries to leave without doing that, stop him and ask to have them
checked. The installer can quickly replace F-connectors on your coaxial cabling and
determine whether there are bandwidth problems with existing splitters or distribution
amplifiers. The result will be improved color and noise in the analog channels, and
infrequent or nonexistent pixelization or sound-loss problems on digital or HD channels.
...Doug Blackburn
db@hometheatersound.com |
