Aaronia SPECTRAN HF-2025, Руководство пользователя

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15.3 Cell towers
Cell towers can be seen nearly everywhere these days.
There are only a few places (like large woodlands) which
are still “radiation free”.
The most obvious installations are the up to 100m high cell
towers (base-stations). In case of only a few customers
needing service, these base stations consist of so-called
omnidirectional antennas (mostly one transmitting antenna
in the middle and two reception antennas at either side).
Here, the radiation spreads almost equally in all directions.
Most base stations however can provide service to a much
larger amount of customers. In these cases, a group of
antennas (so-called radio cells) is installed on radio towers
which then only provides service for a certain direction (so-
called sector). Here, when doing measurements, you will
measure different amounts of radiation depending on the
position of the antenna group (see also the radiation pat-
tern on the left). Using this antenna technology, a signifi-
cantly higher transmitting power is possible, using the
same amount of space and the same licensing class. In
most cases, you will find the version with three radio cells
(triangular installation with 3 sectors spanning 120 degre-
es each, see image). Here, you will find a transmitting
antenna on every side, with two similar reception antennas
on either side of the transmitting antenna.
Construction of these “antennas” is very different from that
used for “regular” rod antennas (see picture). They rather
resemble some kind of “fence post”.
All radio cells together make up a huge transmitter network
available all over the country, always appearing as a
single, always optimally working radio cell to the user. In
practice, this works as follows: Say you are walking
through a pedestrian area, placing a call with your cell-
phone. Your phone will automatically recognize which cell
is closest and yields the best reception, and constantly
“jump” automatically to that with the best reception quality,
such that you will always have an optimal, drop-out-free
reception. This whole procedure happens unnoticeable for
the user.
Omnidirectional base
station with a single cell
Sector-base station with
3 radio cells. Each cell
serves a 120 degree
sector
Layout of the base stati-
on shown above
Cone-shaped radiation
diagram of a sector
(seen from above)
15.0 RF exposure in practice
53