e. Frequency diversity. In frequency diversity, the same information is sent simultaneously on
more than one frequency. Because of lack of correlation of fast fading over a path on different
frequencies, a strong likelihood exists that the carrier and all sidebands will not fade out together, and at
least one frequency will nearly always be received. Such a system is wasteful of bandwidth, but offers
advantages in certain applications where a space diversity system is not feasible. It can be combined
with space diversity further to reduce error rates.
f. Space diversity. This is the only technique that has been used extensively on long-range
tropospheric scatter circuits. It is the most commonly used form of diversity when sufficient ground is
available.
Dual space diversity (use of two paths) receiver-antenna configuration provides
approximately 99.9 percent reliability in a 100-mile point-to-point communications circuit, providing
the scatter volume height and scatter angle are kept low. To obtain the same circuit reliability with a
single receiver-antenna system would require either an increase in transmitter power, a decrease in
receiver noise figures, or an increase in overall antenna gain. In a space diversity system, the outputs of
the individual receivers are switched or combined in such a manner as to ensure the best possible signal-
to-noise ratio in the final diversity signal.
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