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components that were used as well as the mast height should be noted at this time.
You should also create a simple drawing of the antenna installation, including
structural supports and ground system relative to the layout of the house, generally
drawn on the back of the work order.
Testing for Signal Strength with a Site Survey Rig
The first step of the site survey is to verify where the best signal reception is
accommodated on the customer’s home. Most installers are provided with a test kit that
includes a lightweight, telescoping, fiberglass push-up mast with attached antenna.
The antenna gain should be specified by the system engineering staff.
The most satisfactory method to ensure clear and adequate system performance is to
achieve a signal-to-noise (S/N) ratio of at least 30 dB. This ratio is measured using a
signal level meter/QAM analyzer and may be calculated for California Amplifier
transceivers with reasonable accuracy, using the formula below:
S/N = 25 + Transceiver IF Output Level (in dBmv)
TECHNICAL TIP
: When reading signal levels, an installer must always be aware of
physical factors that can affect system performance. Microwave signals are highly
susceptible to absorption by trees and other foliage. A wireless antenna thus cannot
view the transmitter from behind a tree. Distant trees can also cause reception
problems. While they may not be visible to an installer, they may still lie in the
transmission path.
Signal fluctuations exceeding 2 dB during a survey may be an
indication of distant foliage problems
.
Foliage from winter to summer will affect the strength of the received signal. Trees that
are barren in the winter present very little signal attenuation. In the summer when the
trees are full of foliage the attenuation can be as high as 10 dB per tree in the line sight
path. NEVER attempt to receive a signal through a barren or partially barren tree.
Of course, hills and large buildings can completely obscure or deflect microwave signs.
Still other interesting problems can result when the microwave beam grazes the top of
a hill or building, partially deflecting the beam, or when reflective surfaces (bodies of
water, buildings, etc.) cause multiple signal paths from the transmitter into the receive
antenna, a problem known as “multi-path” can occur.
Never use a signal received from a reflection as its reception characteristics can change
drastically over time. Only line-of-sight signals should be used.
