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The camera is aimed due south. Note the AT&T cable Right Of Way warning sign (but I didn't record what kind of cable. Sorry.)
There are usually three antennas on most routes. One of them is a Space Diversity antenna and usually is 50-100' lower or higher than the other two antennas, as on the shorter tower. It is interesting that on the higher tower at North Bend all three seem to be clumped together.
Multipath Distortion/Space Diversity Explained: Two antennas were installed originally - one to transmit and another to receive the microwave radio signal. Over time, it was discovered that the received signal would fade away momentarily. It turned out that the microwave beam, which is quite similar to a flashlight beam, suffers from Multipath Distortion. Just as you often can see a mirage of water (a reflection of the sky) on the road on a hot day, microwave beams will also reflect off an atmospheric "mirror" just above the ground or a cooler river valley. A receiving antenna will then receive two signals - one directly from the far transmitting antenna, and another which has reflected as a "mirage".
The reflected signal takes a longer path and arrives later than the direct beam such that the reflected radio waves may arrive one-half of a wavelength later and are 180 degrees out of phase with the direct signal. Unfortunately, when received, both radio signals cancel each other out. Then all hell breaks loose: Half of the parties on hundreds of affected calls cannot hear in one direction, and idle trunk circuits - all at the same time - falsely appear to be going off-hook and trying to originate many, many calls into long distance switching systems all over America. The fade would last for a few seconds until a puff of wind destroyed the atmospheric mirage.
Back at the offending towers, AT&T found that the multipath distortion was very localized, such that a reasonably good signal could still be received at a location further down on the tower. Using this knowledge, AT&T added a second receiving antenna (making a total of three aimed in the same direction), and electronic gear to automatically select whichever antenna was receiving the best signal.
There are usually three antennas on most routes. One of them is a Space Diversity antenna and usually is 50-100' lower or higher than the other two antennas, as on the shorter tower. It is interesting that on the higher tower at North Bend all three seem to be clumped together.
Multipath Distortion/Space Diversity Explained: Two antennas were installed originally - one to transmit and another to receive the microwave radio signal. Over time, it was discovered that the received signal would fade away momentarily. It turned out that the microwave beam, which is quite similar to a flashlight beam, suffers from Multipath Distortion. Just as you often can see a mirage of water (a reflection of the sky) on the road on a hot day, microwave beams will also reflect off an atmospheric "mirror" just above the ground or a cooler river valley. A receiving antenna will then receive two signals - one directly from the far transmitting antenna, and another which has reflected as a "mirage".
The reflected signal takes a longer path and arrives later than the direct beam such that the reflected radio waves may arrive one-half of a wavelength later and are 180 degrees out of phase with the direct signal. Unfortunately, when received, both radio signals cancel each other out. Then all hell breaks loose: Half of the parties on hundreds of affected calls cannot hear in one direction, and idle trunk circuits - all at the same time - falsely appear to be going off-hook and trying to originate many, many calls into long distance switching systems all over America. The fade would last for a few seconds until a puff of wind destroyed the atmospheric mirage.
Back at the offending towers, AT&T found that the multipath distortion was very localized, such that a reasonably good signal could still be received at a location further down on the tower. Using this knowledge, AT&T added a second receiving antenna (making a total of three aimed in the same direction), and electronic gear to automatically select whichever antenna was receiving the best signal.