Quote:
Originally Posted by Stuart
The science is simple... The Antennas used only transmit from the side (note: The Antennas I refer to are inside the protective casings we see mounted on the Mobile base stations). As such, they are oriented so that they transmit out of the side of the base station, where the signal will reach the most users, rather than downward, where the only thing receiving the signal will be the earth and a couple of people standing by the base station.
To ensure that the signal reaches the maximum amount of people possible, the base station is normally mounted quite high, as gravity does (slowly) affect the path taken by radio signals.
As such, by putting the mobile mast next to the school, the signals it generates will be flying several metres over everyone's head.
TV and radio transmitters also suffer the same limitations, but they have to transmit over a wider area, hence they can be hundreds of feet tall (600 odd in the case of Crystal Palace).
That's a gross simplification, but I believe I've explained the basics quite well.
|
Gravity?????
It's down to the horizontal polarisation of the base station aerials which is by design. Known as Beamwidth or lobes. They are designed for location and channels they can handle.
There are normally three aerials/operator/base station to give you 120 degree segments.
Rural base stations are high for reasons you state, but you get micro/pico cells to cover a very small specific areas. I live close to a microcell and the mast is about 50 feet high and probably can only handle about 16 simultaneous calls. The aerials will be designed to have short range but large bubbly lobes that extend down to about 10 feet at close range. The high base stations hand signals down to these. Known as Umberellas.
You cannot have large lobes that travel a long way (like TV transmitters) without maxing the output power. Crystal Palace in is the order of 5Megawatts IRRC as it covers out as far as Hampshire.
A school base station (picocell) could easily be the size of small cabinet in a school room.
However with kids these days and the amount of phone use at schools, you may need a full power base station/desk
Normally Wikipedia can contain trash explanations, but I believe as an engineer is a pretty good simple explanation in para 1.
http://en.wikipedia.org/wiki/Picocell