Cisco BR1400 Deployment Manual page 21

It is possible to create a nearby bridge link through a window
Figure 16.
4.1 Determining Line of Sight
Since radio waves used by the BR1410 are very high in frequency (5.7 GHz / 5700 MHz) the
radio wavelength is really small, therefore; the radio waves don't travel nearly as far given the same
amount of power as radio waves on lower frequencies. This higher frequency range makes the
Bridge ideal for unlicensed use as the radio waves do not travel far unless a high gain antenna is
used that can tightly focused the radio waves in a given direction.
Tip: High gain antennas can focus radio waves allowing them to go much further similar to
adjusting the focus of a flashlight from a flood type light into a tight beam.
Line of Sight disappears at 6 miles (9.6 Km) due to earth curve.
Figure 17.
The higher the frequency used the more dependent you are upon line of sight, and the BR1400
Bridge using 5.7 GHz requires line of sight for successful operation. As the low powered radio
signals degrade over distance, this is known as free space path loss or simply path loss. It difficult
to acquire and sometimes easy to lose a bridge link when attempting to transmit radio waves
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