In article <
6kepvd5m3sf4ijcd8...@4ax.com>,
Peter Jason <mmmm> wrote:
>Does this apply to TV interference too? My TV
>works only on some channels and the rest show "no
>signal" or severe pixellation. Also, the trouble
>is intermittent. What can I do? Is there some
>sort of filter to fix it?
The first question I would ask is, "What's your antenna setup?"
For TV, and for FM radio, the most important aspect to getting good
signal quality is having a good antenna arrangement - a proper antenna
mounted where it can "see" the transmitters with a minimum of
interfering solid matter between the two.
Indoor antennas - "rabbit ears", floppy dipoles, and small wall-mount
panel antennas - are usually suitable only for "strong signal" areas
fairly close to the transmitters. Modern buildings are often quite
effective shields against RF transmission - they contain materials
which either absorb or reflect RF - steel beams, wire mesh in stucco
walls, metallized plastic insulation and vapor barriers, and so
forth. Signals from distant stations don't stand a chance... they're
weakened, and also degraded by multipath (multiple RF paths of
different lengths, caused by signal reflections, which result in
frequency-selective signal reinforcement and cancellation).
The results of all of this are bad signals. Analog TV suffers from
noise and "ghosts". FM suffers from noise and distortion. Digital TV
suffers from pixellation, freezing, and "no signal found" problems.
These problems can all be made worse by local interference, radiated
or conducted. They're also made worse by short-term multipath -
e.g. signal reflections from airplanes flying within the
line-of-sight, or even trucks driving by on the road outside. On FM
you can hear a "picket fencing" effect when this happens, on analog TV
you see moving "ghosts", and on digital TV you see pixellation and
freezing. Digital TV receivers do have the ability to detect and
cancel out some multipath reflections, but dealing with rapidly
changing reflections is a "hard problem" for them and they often don't
adapt fast enough.
Filters at the receiving end (TV, FM radio) won't help, except in the
case where the TV is picking up _conducted_ RF interference through
the power line. Can't hurt to try, but don't expect miracles.
Filters at the sources of interference (noisy motors, PC power
supplies, LED lights, light dimmers) may help somewhat. However, even
if you completely filter all local noise sources, there can still be
plenty of noise from outside the house/apartment - neighbors'
equipment, etc.
The real "fix" is to improve the quality of the incoming RF
signal... you want a strong signal with minimal multipath. This often
requires an outdoor antenna - one mounted up "in the clear" (e.g. on a
roof mast). If possible, install a directional antenna which is aimed
in the direction of the desired transmitter - this both boosts the
amount of "good" signal (thanks to the antenna's gain) and also
reduces the amount of "bad" signal (multipath reflections coming in
from other directions, and random interference from sources in the
area). If necessary, install a remote-controlled antenna rotator, or
an electronically-rotatable antenna (if your TV has the ability to
control one of these - most do not, I believe).
If you're getting your over-the-air TV signal via a cable-TV feed, and
the quality is still poor, then check your coax connections, and/or
complain to the cable company.