oldhandPremium
join:2003-05-16
Saugus, MA
| Back to technical reality... In the 5 GHz band, line of sight often isn't sufficient, primarily due to the ease with which the RF signals are reflected. The problem is that each reflection causes a polarity reversal that can lead to signal cancellation by the out-of-phase reflection. As reflection efficiency is very high in this region of the spectrum, the 30-40 mile links described in prior posts often depend upon dual receive antennas vertically separated by a distance calculated so that only one antenna can receive a cancelled signal at any given time. Even with such extreme measures, high-gain parabolic antennas (typically 6' to 8') are required at both ends so that when combined with low-power transmitters, the spectrum isn't swamped for other users. The bottom line is that this frequency band will only be practical for broadband use if power levels are severely limited, and even then, spread-spectrum technology would ideally be implemented to limit multi-path anomalies.
Regarding another posting, the primary path length limit for a microwave signal is rainfall attenuation, which increases as a function of frequency. Even though a transmission to a satellite may cover a long distance, the only area of rainfall attenuation is in the lower atmosphere, which rarely exceeds 10-miles. |
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 FobulousPremium
join:2002-08-14
Missouri City, TX | am i wrong or does 5 ghz have shorter range than 2.4gh. |
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oldhandPremium
join:2003-05-16
Saugus, MA | When rain is present, a 5 GHz signal will indeed deliver a shorter range than a 2.4 GHz signal. As the frequency increases, the size of the raindrops approach that of a theoretically perfect antenna. At that point, the transmitted power is effectively just warming the rain. |
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