Link Engineering and RF Path Planning
Alignment and interference

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.