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What is the concept of "true diversity reception" in wireless microphones?

ITdrummer

What is the concept of "true diversity reception" in wireless microphones?
Thank you,
Mike
September 25, 2012 @03:32pm
JeffBarnett

What is the concept of "true diversity reception" in wireless microphones?
Thank you,
Mike

True diversity is a technology built into most quality wireless mic receivers. In a true diversity system, two antennas are used, spaced at least a few inches apart, each receiving the same signal from the transmitter. The receiver constantly measures the signal strength coming from both antennas, and switches to whichever antenna is picking up the stronger signal.
The reason for this is that as RF energy from the transmitter bounces around various surfaces in the room, sometimes reflections can interact with each other destructively, and cancel themselves out. This causes what is commonly called a "dropout" - a momentary loss in signal. Dropouts are location-based, and dependent on the placement of both the antenna and the transmitter. When one antenna experiences a dropout, it is likely that the second antenna will have a strong signal. While a true diversity system doesn't guarantee that there will be no dropouts, it will dramatically reduce them.
A diversity scheme is "true" diversity if the two antennas are connected to independent receiver modules. In less-effective diversity schemes, the two antennas are connected to a single receiver, which cannot monitor the signal strength of both antennas at the same time. In these "quasi-diversity" systems, if the signal drops below an acceptable level, the receiver will switch antennas blindly, not knowing what the signal strength on the other antenna is until the switch is complete. This sometimes can make things worse, not better.
There are even a few non-diversity wireless systems out there (thankfully not many any more) which appear to have two antennas, but actually just have one antenna which pokes out of the chassis in two places. In these systems, no signal switching is possible since the two antennas are really just a single antenna. Sometimes this is called "passive diversity," but it's really not a diversity scheme at all.
September 25, 2012 @04:15pm
Dave Burris

There are a couple of varieties of diversity, thus the term "true diveristy" is a bit confusing. There are also differences in the way diversity is used in combination with other features to offer seamless protection against most RF dropouts. Some of these schemes work better than others, along with the increased cost and complexity of the solutions, thus the variance in price.
Jeff's description is reasonably accurate. The exception is the description of switching diversity. In this case, there is only one receiver with two antennae. Both antenna are not monitored in this case because to do so would require switching to an antenna with a potentially bad signal (dropout). The approach relies on the detection of the signal on the active antenna being monitored for what appears to be a dropout. This case relies on the statistical probability that the inactive antenna is receiving a better signal that the one about to go bad. It assumes reasonable signal levels and dropouts caused by reflections, etc.
The variety and cost of diversity schemes vary in their affectiveness in eliminating dropouts in less-than-optimum signal conditions. The more advanced schemes offer better signal-to-noise performance, better end-of-range performance, and less audio artifacts during the switch, along with some assurance that you are indeed switching to a better signal.
I believe a quick web search would turn up some white papers on the topic that offers much more detail of the technologies in question.
Added note:
On second reading of Jeff's post, I will repeat that it is a reasonably accurate description of some of the methods available.
September 26, 2012 @12:00am
ITdrummer

Thank you guys for the help!
September 27, 2012 @02:01am