Transmitter power is more likely 10-20W per carrier into one of three 12
dBi sector antennas. This amounts to soumething on the order of 300-400
watts effective radiated power(ERP).
However, the antenna gain which produces the 12 dBi sector pattern
actually means that the 20 watts coming out is spread over a larger,
rather than a smaller (dipole sized or 1.5 by 3 inches at 1900 MHz).
This means that even a bird sitting on the antenna, is potentially
intercepting a much smaller fraction (12 dB would be about a factor of
1/16 ) that it would have seen with a lower gain antenna.
Even if the bird managed to absorb the maximum possible, it wouldn't
be enough power (1 watt territory) to do much. While there might be
several carriers on the one sector antenna, the bird doesn't absorb all
the power and ismore in danger of being seen and eaten by a hawk than
getting injured by RF.
The cell transmitters run more power than handsets because for voice
calls, they are serving ~60 or so users and for data calls, they have to
get more signal to the handset in order to be able to deliver higher
data rates in the voice-only coverage area. For a loaded
CDMA carrier,
the base power could be as low as 20/60 = .33 watts which is about the
same as the handset would max out at. This makes sense since for a
voice call, the 10 kbps data to support voice has to be fully
bi-directional. For a data call, most systems are assymetric and offer,
for example, 600 kbps down and 100 kbps up.
g
>>>> I saw several birds happily sitting on a cell phone tower yesterday.
>>>> They were sitting right on the antenna panels! Why didn't they fry and
>>>> fall-over dead? Don't these cell phone panels radiate about 100 watts
>>>> of power?
>
> I believe it's more like 40W, so you might as well think of it as a bird
> sitting very close to a 40W light bulb: That's a small enough power source
> that they'll probably feel themselves getting hot (and move!) well before they
> "fry." This also assumes birbs absorb heat well at cell phone frequencies,
> although this is probably a good assumption.
>
> Pager towers used considerably more power (a couple hundred watts), if I'm
> remembering correctly.
>
>>> Why? It seems to me(not knowing) that they wouldn't need much more than a
>>> given Cell phone outputs. I mean, if a Cell phone uses anywhere from .06
>>> to .6 watts of power to contact a given Cell tower, why would that tower
>>> need more than that to transmit to that given Cell phone?
>
> Cell towers transmit far more power than cell phones transmit because the
> phone is at a distinct disadvantage when trying to *receive* that signal: They
> only have one, small antenna. (Whereas, when the tower has to receive from
> the handset, it has *multiple* *large* antennas to do so with.) Hence, as the
> tower isn't particularly power constrained, it uses additional transmission
> power to make up for the poorer receive abilities of the handset.
>