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“Optimal Combining” Diversity ?
I ran across a couple of interesting discussions started by W5UN and K1UO on diversity reception. Below are the links and excerpts from Steve’s (N5AC) replies:https://community.flexradio.com/flexradio/topics/6700_vs_k3_still_no_contest
“The situation is this -- not only is the FLEX-6700 capable of what I would call "antenna diversity with human decoder" where you stick two receivers that are locked, one in each ear (a.k.a. poor man's diversity), the FLEX-6000 has the necessary hardware to support MRC/optimal combining. Poor man's diversity is essentially a form of what is called selection diversity where two ears are used to actively select the best of the signal at any point in time. This is how classic voting receiver systems worked on repeaters as implemented by GE and Motorola in the day. With selective diversity, two signals with different SNRs are presented to a voting system (electrical or your ear) for the selection of best SNR at any point in time.”
“In contrast, MRC/optimal combining is different in that DSP is used to look at the correlated signals (the ones you want) and non-correlated signals (noise) and then subtract out the noise. This nominally provides a 3dB SNR improvement on the signal you give to your brain. This is really a big difference -- it can essentially lower the noise floor by 3dB at your location. Again, this can be 3dB better than the BEST of the two signals you get off the two antennas which is not possible with selection diversity.”
“Additionally, we have a mechanism in the FLEX-6700 to take a single antenna and run it to two data converters. This is also another form of diversity, but it aims to lower the noise floor of the data converters.“
“Two of the diversity forms we discussed -- the linked slice or simple diversity method and the optimal combining method -- made the cut. The first method we plan to do in v1.3 and the second is more of what we call a science experiment. In other words, we want to do some research and testing to find out what works best before we commit to a date. When we do this, we generally do not put the item on the roadmap because we do not want to have to come back and say "well it doesn't look like it will make xyz release after all." Having said this, we have already started work on optimal combining and the quicker that work comes to conclusion, the quicker you will see it in the software.”
Assuming that the current implementation is the “simple diversity” version, is MRC/optimal combining, and/or routing a single antenna to 2 data converters to lower SNR, still in the works, even if in the science project stage?
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