[c-nsp] High-power 802.11b/g repeaters

[Jay Hennigan]

Howard C. Berkowitz wrote:

> I have an application where a WLAN repeater will be in a high outdoor 
> location (e.g., a tethered balloon), and, as I understand, there is a 
> way to make certain repeaters run higher power than is advisable 
> indoors. Can anyone point me to a document on the settings and range 
> assumptions (of course, the latter is antenna-dependent).

Transmitter output power is a function of the hardware, although 
typically adjusted by software.  There are regulatory limits as to the 
amount of transmitter power that one can run without an FCC license, as 
well as regulatory limits for human exposure to electromagnetic fields. 
  As a rule the human exposure limits are not going to be a concern with 
low power unlicensed radios.

However, range is dependent on effective radiated power which included 
transmitter output power and antenna gain as well as feedline losses. 
Effective radiated power is also regulated by FCC.

Your problem will be with the antenna gain.  Antenna gain is achieved by 
concentrating the beam.  A theoretical isotropic antenna radiates int a 
spherical pattern.  An actual dipole radiated more in a pattern shaped 
like a torus (donut).   By "squashing the donut", you can concentrate 
energy at the horizon as opposed to warming the ground and sending 
unwanted energy into space.

If your desired receiver is in a specific place, directional antennas 
can concentrate the energy to a specific horizontal azimuth.  This also 
helps reduce interference and if used at the receive side increases the 
effective sensitivity of the receiver.

However, with a tethered balloon, unless it is gyro-stabilized, antenna 
gain is likely to do more harm than good as the tilt and rotation of the 
balloon in the wind will result in highly variable results.

Short answer, transmitter power is usually adjusted in software but may 
have preset limits for regulatory compliance below what the actual 
hardware is capable of producing.  Procedures for adjusting will depend 
on the radio that you are using.

-- 
Jay Hennigan - CCIE #7880 - Network Administration - jay at west.net
NetLojix Communications, Inc.  -  http://www.netlojix.com/
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