When aligning antennas, be sure that the two antennas for the link are not
cross-polarized. Next, ensure that each antenna is pointed or aligned to
maximize the received signal level. As shown in Figure
, a signal
strength tool is provided, which gives a reading of the received signal level.
At one end of the link at a time, the antenna pointing direction is carefully
adjusted to maximize or peak the reading on the signal-indicator tool.
After this is done for both ends, it is very important to obtain the actual
received signal level, in dBm. This is to verify that it is within 0 to 4 dB of
the value obtained from the link-budget calculation. If the measured and
calculated values differ by more than 8 dB, check the antenna alignment, and
then look for a defect in the antenna transmission line system. A wireless link
path crossing through the path of another link will not cause interference.
This is because any type of radio or other electromagnetic signal that is
propagating through space or air will be unaffected by any other signal that
crosses the same point in space. This can be demonstrated by using two
flashlights. Shine one flashlight onto a wall. Hold the other flashlight a
distance away from the first, but point it so that the two light beams cross.
Notice that the beam from the second flashlight has no effect on the spot on
the wall from the first flashlight. The same is true for radio signals of any
frequency. If the second flashlight is shined onto the same point on the wall,
the spot will appear brighter. Likewise, if the beams were radio signals of the
same frequency, and if the spot on the wall was a receive antenna for one of
the links, the second beam would likely cause interference. Note, however, that
this is a different situation than when the beams are crossing in space.
A wireless link path is usually unaffected by utility lines that run
perpendicularly through it. This is because the wires appear to be infinitely
long conductors. This causes a slight diffraction effect on the signal
propagating across them. This slight diffraction is usually immeasurable.
For RF systems, rainfall and other precipitation attenuation is not
significant below 10 GHz. Figure
graphs
how rainfall affects higher frequencies more than lower frequencies.