THE best ideas are often the simplest—and a new patent designed to
quell the spread of cellphone and digital TV masts could be one of them. Instead
of building unsightly new cellphone towers, says British electricity utility
Norweb, why not put the antennas on electricity pylons?
Rising demand for mobile phones means that cellphone network operators are
building more antennas. Rival networks don’t like sharing transmitter sites
because each wants to offer better coverage than its competitors. To complicate
matters further, a “third generation” of digital cellphones will soon be added
to the existing four networks, and the government’s Independent Expert Group on
Mobile Phones may make new safety recommendations for the siting of cellphone
towers, in a report due out in April or May.
Digital TV is also creating a demand for more transmitters, since only 85 per
cent of British homes can receive the transmissions at the moment. Chris Smith,
Secretary of State for Culture, Media and Sport, told 91av:
“Analogue TV reaches 99.4 per cent of the population. Covering the last 15 per
cent with digital transmitters would be horrendously expensive and would litter
the countryside with masts. We need to look at other options.”
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Electricity pylons are not tall enough to transmit powerful radio signals
over a wide area, but digital signals are weaker—with more restricted
cover to avoid interference with analogue services elsewhere on the same
frequencies. Cellphone transmitters are even weaker still—so shorter masts
are acceptable there, too.
Norweb, part of the United Utilities conglomerate, supplies electricity to
the north-west of England. Paul Brown, the inventor of Norweb’s system, has
since left the company.
Brown found that although pylons are earthed to make them safe, it is
possible to stop a radio signal leaking into the ground via its earth cable by
carefully choosing the height at which the antenna is mounted. Because the radio
signal creates a “standing wave” in the earth cable, the points at which the
wave reaches a null point can be made to sit at the base of the mast—so no
energy leaks into the ground.
But a spokesman for NTL, which transmits Britain’s commercial TV and radio
signals, is not impressed with Norweb’s idea. “The power cables are at high
voltage and the transmitter needs low voltage. Security is an issue too. Pylons
are not tall enough or in the right places,” he says.
Brown thinks NTL is wrong. “Towers for 132-kilovolt cables are between 22 and
44 metres tall. They run along roads and into urban areas, where the signals are
needed,” he says. Digital TV is hard to receive in hilly areas, but pylons
bringing power along the roads could be used to overcome this problem. In
addition, Brown says, transmission amplifiers can be located at substations
which are already secure and equipped with low-voltage power. “No planning
permission is needed for the pylon because it’s already there,” he says.
