User guide

Designing Your Canopy Network March 2005
Through Software Release 6.1
Issue 1 Page 99 of 425
Canopy System User Guide
6. Click Enable again.
RESULT: The system measures RSSI and dBm for each frequency in the
spectrum.
7. Travel to another location in the area.
8. Click Enable again.
RESULT: The system provides a new measurement of RSSI and dBm for each
frequency in the spectrum.
NOTE: Spectrum analysis mode times out 15 minutes after the mode was
invoked in Step 5.
9. Repeat Steps 7 and 8 until the area has been adequately scanned and logged.
As with any other data that pertains to your business, a decision today to put the data into
a retrievable database may grow in value to you over time.
RECOMMENDATION:
Wherever you find the measured noise level is greater than the
sensitivity of the radio that you plan to deploy, use the noise level (rather
than the link budget) for your link feasibility calculations.
12.2.2 Anticipating Reflection of Radio Waves
In the signal path, any object that is larger than the wavelength of the signal can reflect
the signal. Such an object can even be the surface of the earth or of a river, bay, or lake.
The wavelength of the signal is approximately
◦ 2 inches for 5.2- and 5.7-GHz signals.
◦ 5 inches for 2.4-GHz signals.
◦ 12 inches for 900-MHz signals.
A reflected signal can arrive at the antenna of the receiver later than the non-reflected
signal arrives. These two or more signals cause the condition known as multipath. When
multipath occurs, the reflected signal cancels part of the effect of the non-reflected signal
so, overall, attenuation beyond that caused by link distance occurs. This is problematic at
the margin of the link budget, where the standard operating margin (fade margin) may be
compromised.
12.2.3 Noting Possible Obstructions in the Fresnel Zone
The Fresnel (pronounced fre·NEL) Zone is a theoretical three-dimensional area around
the line of sight of an antenna transmission. Objects that penetrate this area can cause
the received strength of the transmitted signal to fade. Out-of-phase reflections and
absorption of the signal result in signal cancellation.
The foliage of trees and plants in the Fresnel Zone can cause signal loss. Seasonal
density, moisture content of the foliage, and other factors such as wind may change the
amount of loss. Plan to perform frequent and regular link tests if you must transmit
though foliage.