TV AERIALS -- HINTS AND TIPS
Itís surprising how many
people are prepared to spend a thousand pounds or more on a large-screen
television, then expect to get a decent picture from a twenty-year old TV
aerial, gently corroding on their roof. Modern TV tuners are extremely
sensitive and very good at eliminating ghosting effects but TV reception doesnít
only mean picture and sound, NICAM digital stereo signals can be adversely
affected by reflections and multi-path transmissions, but the most vulnerable
part of the signal is teletext data which is easily corrupted, even when the
picture looks reasonably good.
Obviously it is important
to have a good aerial, but what exactly does that mean? For someone living in
the immediate vicinity of a TV transmitter a high-gain antenna can actually be
a disadvantage; too strong a signal can produce just as bad a picture as a weak
one. Within half a mile or so of the Crystal Palace transmitter in South
London, a two-inch nail stuck in the TVís aerial socket is usually more than
sufficient... (Just a joke, please donít try it or weíll be had up for
something or other).
Choosing the correct TV
aerial neednít be difficult though; to get a rough idea of what needed take a
look at whatís on the neighbourís roofs, it can tell you a lot about local
reception conditions, including the direction and proximity of the TV transmitter
serving your area; however, if you see a lot of complicated aerials on long
poles, pointing in different directions youíre almost certainly in a fringe
reception area, and you will definitely need specialist help, weíll come to
that in a moment.
You can usually tell how
good or bad the signal is by looking at the construction of your neighbourís
aerials. TV aerials have three basic parts, the spar, a reflector and the elements.
The spar holds everything together, the reflector is mounted at one end, itís usually
a perforated flat plate mesh or two smaller spars with rods radiating sideways.
The elements are a series of horizontal or vertical metal rods, spaced along
the length of the spar. In strong signal areas 10 or 12 elements are the norm,
but as the signal gets weaker more elements are needed, 14 with a medium
strength signal, and 18 when the signal is struggling to get through. If the signal
is really poor or there are local problems with buildings or structures in the
way it might be necessary to fit a really elaborate high-gain aerial, and
possibly a booster amplifier as well.
If thereís only a few small
aerials to be seen signal strength is probably very good, or youíre in a
conservation or housing association area, where the houses are served by a
communal aerial or cable TV. If thatís the case youíll probably have to comply
with local regulations, otherwise, when thereís a good strong signal you have two
alternatives. The best one is a loft aerial, these can be ordinary 10-element
aerials installed in the roof-space. If thereís a problem with cabling or you
donít have a loft, the last resort is an indoor set-top aerial. Set top aerials
prove that thereís still a strong element of witchcraft in antenna design, take
manufacturerís claims with a hefty pinch of salt, especially those that purport
to perform as well as loft or rooftop aerials, they donít. You can also give
any set-to aerial fitted with a miniature satellite dish, a very wide berth,
not only are they incapable of picking up satellite TV they usually not much
good at receiving terrestrial signals either.
Installing a rooftop aerial
yourself is not a good idea; apart from the obvious safety implications, itís
no fun running up and down ladders if you havenít got the proper tools and
equipment. It is usually best to leave this kind of job to the professionals,
at least youíll have someone else to blame if it falls down or goes wrong. Aerial
installers can be a funny bunch, though, so talk to at least a couple of local
firms and consider any personal recommendations, before you make up you mind.
If youíve got a choice, go for the one whoís a member of the CAI (Confederation
of Aerial Industries), they should have demonstrated a minimum level of
competence, and should have the necessary insurance cover.
ANTIFERENCE Telephone (0296) 82511
BLAKE AERIALS Telephone (0742) 759729
CONFEDERATION OF AERIAL INDUSTRIES. Telephone 081-902 8998.
MAXVIEW AERIALS Telephone (0553) 810591
TRIAX AERIALS Telephone (0763) 216755