Topband: beverages: Diversity / Phasing

[Ken Brown]

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Hi Tom,

It seems like people are using the term "diversity" incorrectly. I don't 
have an authoritative definition. It would be interesting to know what 
people think diversity is. I can think of a few things which are NOT 
diversity. Adding the RF from two or more antennas (perhaps using 
combiners, phasing lines, variable attenuators, or phase shifting 
networks) is a "phased array" and is not diversity. It is my 
understanding that "diversity" choses the signal from the antenna which 
has the best S/N ratio or bit error rate. This is often done using 
separate receivers AFTER the signals have been demodulated and are 
audio, or a data stream. If some kind of control is selecting the best 
antenna going to a single receiver, it might also be called diversity. 
In microwave communications the terms "space diversity" and "frequency 
diversity" are used. Space diversity uses two antennas, two receivers 
and some sort of "voting" system to select the better signal. Frequency 
diversity requires all of that and two transmitters at the other end on 
two frequencies. If the "selection" of best signal is done in the 
operators head, using separate signals in each ear, maybe that is also a 
form of diversity. Perhaps a phased array with some kind of control loop 
dynamically adjusting the relative phase and amplitude from the two or 
more antennas would also be a correct application of the word "diversity"?

I would be interested to know what is the real defintion of the word 
diversity in the context of RF communications?

Ken N6KB