cable TV. Okay, now, everybody who actually
reception, keep your hands up. Not many, are there? That's what I
thought.
Most videophiles I know have a love-hate relationship with cable
TV: they
they
static, and the periodic cable outages that only seem to come up
when you're trying to record the last showing of your all-time
favorite film from pay TV.
Can anything be done to improve the quality of cable TV?
Plenty...but unfortunately, most of it has to be done at the
end>, which is the central receiving office of the cable company.
Without a good signal to begin with, the best-quality cable
amplifiers and wires in the world can't bring a decent picture
into your home. In addition, many cable companies operate under-
less-than optimum budget conditions, preventing them from using
state-of-the-art gear, for everything from inadequate line
amplifiers on the telephone pole to shoddy channel-selector boxes
in your home.
There are a couple of things you can look for to help the cable
repairman solve the usual problems: perhaps the biggest is
or video noise, which is generally caused by inadequate signal
levels. Most experts advise that an average tuner needs at least
.1 millivolt of signal to produce an acceptable picture. A little
more, like around .3 mV, is even better. Cable TV companies
routinely use amplifiers in their lines placed at regular
intervals so that people far away from their headquarters will
a block from the head end.
If a little signal is good, then a lot of signal must be even
better, right? Wrong. In VHF/UHF transmissions through cable, the
biggest loss is with the high frequencies, especially channels 25
and up. The cable company's amplifiers use special "tilt"
equalization to help peak these frequencies, which helps reduce
the loss over a long distance. If the cable amps are improperly
adjusted, the lowband channels (2-13) suffer, resulting in a lot
of ghosting and intercarrier interference. The latter is the
typical "buzzing" you hear when bright titles pop on the screen.
Another problem is "tearing," when bright signals streak or smear
from one side of the screen to the other.
You can cut back on the cable line's signal with a inexpensive
device called an
that screws directly between your cable and the tuner input. An
attenuator works by reducing signal strength with an electrical
filter, sort of like using an adjustable spray nozzle on a garden
hose. Attenuators are rated in decibels (dB), and range from as
little as 5 dB all the way to 20 dB and up -- the higher the
number, the more severe the effect. Sometimes, just
the signal to several TV sets or VCRs will help cut down the
signal to a proper level, too, using a multi-output RF splitter,
available for about $20 from Radio Shack and other companies.
If your cable pictures are marred by snow and ghosts, you've
probably got the opposite problem:
Recoton and several other accessory companies make consumer
VHF/UHF signal amplifiers which can help strengthen weak cable
signals. But it's easy to misadjust these amps and create some of
the problems mentioned above. Experiment carefully, and make sure
the reception is clean on
setting for your system. This is especially important when
connecting more than two or three devices to one cable signal.
Another common cable TV problem is
like large horizontal bars rolling through the picture. Usually,
these roll rather slowly, which are a sign of 60 Hz hum (the same
frequency as AC current). Hum in cable systems like this happens
when your house current is grounded differently than the cable
system's current. This visual hum is often accompanied by low-
frequency hum or buzzing in the audio, and is particularly
annoying when heard through full-range speakers.
One solution for this common cable ailment is the
This fix consists of two 75-ohm to 300-ohm transformers, also
known as "baluns," which are included free with virtually every
VCR to help connect them to older TV sets with 300-ohm jacks. To
make this device, simply connect the four 300-ohm leads together
so that the round 75 ohm terminals are open. The cable TV signal
goes into one end, and the other end goes to your VCR or TV set.
Voila: the hum is gone, since this double-transformer breaks the
cable's ground and isolates it.
With my own local cable signal, I use Sony's EAC-25 [shown in the
photo], which neatly fits a variety of conventional baluns. The
only drawback with this fix is that you'll lose about 3 dB of
signal, which may introduce a small amount of snow in the picture
if your signal is weak to begin with. Another potential problem is
that the 300 ohm wires may pickup stray transmissions in your
area, which means that strong local stations may affect similarly-
numbered channels on the cable. But that's a small price to pay,
considering the immense improvement for the rest of the stations.
Some cheap baluns that don't use transformers may not fix the hum
problem, but there is a company called Gemini Electronics who
manufacturers a direct 75 to 75 ohm "ground breaker" called the
model #CV89. Their address is Gemini Industries, Inc., 215 Entin
Road, Clifton, New Jersey 07014. This device is a more
attractively packaged and is virtually guaranteed to get rid of
the hum from all but the worse cable systems, with a little less
signal loss than the above method.
And there's one more device you can use to get better cable
quality: the telephone. If you're having severe cable reception
problems, make sure your cable company and local utilities are
aware of the situation. Sometimes, a call to the chief engineer of
your local cable company can work miracles. Just as a squeaky
wheel gets the grease, even the best cable TV company in the world
can't fix problems they don't know about.
[Special thanks to reader Bob Katz of New York, NY for providing
some of the background information for this column.]
# # # # # # # # # #
(Portions of the above appeared in the October '88 issue of VIDEO
REVIEW magazine.)
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