# range calculation

Discussion in 'Cisco' started by herodot, Jan 27, 2005.

1. ### herodotGuest

i ve a The Cisco Aironet 1200 Series(2.4 ghz) and my antenna is 12 dbi
omni i want to buy amplifier 1 watt and 16 dbi amp2440 or amp2441 how
can i calculate the extend area i mean how much km extend ?? (the
formula"?)

herodot, Jan 27, 2005

2. ### Walter RobersonGuest

:i ve a The Cisco Aironet 1200 Series(2.4 ghz) and my antenna is 12 dbi
mni i want to buy amplifier 1 watt and 16 dbi amp2440 or amp2441 how
:can i calculate the extend area i mean how much km extend ??

If you want to be able to extend to kilometers, then instead
There are a few reasons for this:

1) If you are in the USA, Canada, or urban Australia [and likely
a bunch of other places] you are limited to 1 watt EIRP
(effective radiated power). Thus if you were using the amplifier
on what you transmit, then if you are in one of those jurisdictions
you would have to turn down your transmitter power to 0 dbi.
The restrictions in Europe are stricter; I do not recall the
exact figures offhand, but you would probably have to turn
down your transmitter to at least -9 dbi.

2) Amplifiers amplify noise as well as signal. You want more of
the signal to get through, not more noise. Directional antenna
are good for getting more signal through.

3) If your endpoints are fixed, then it is a waste of power to
send the signal out in all directions as an omnidirectional antenna
would: you just want to send to where your other endpoint is.
If your endpoints are moving around, then an omnidirectional
antenna might be suitable, but when your endpoints are moving around
you have the likelyhood that they will move into areas that do
not have a big enough line-of-sight to the base location. A simple
laser-like glimpse of the base location is not good enough:
for radio, you need a bigger clear pathway, known as a Freznel Zone
[which has to do with the fact that radio bounces off objects as
the waves spread out, and the bounced waves can have the effect
of cancelling the original waves.]

4) If you do want to get into long-distance mobile endpoints, then
you are better dropping down in frequency such as to 900 MHz and
a Motorola Canopy system. Lower frequencies are better at penetrating
through obstructions such as buildings and leaves.

Walter Roberson, Jan 27, 2005