(May 16, 2015)
After compiling a lot of video evidences, the facts suggest that, although "MNR" is a very useful index to represent Maximum Non-Reciprocity, "MNR" does not tell the whole story... As demonstrated in this video and also in "Section 7", even when MNR shows that Non-Reciprocity should not be a concern (i.e. low MNR dB values), Non-Reciprocity can still be very severe and "lethal".
Why is that? The explanation is simple. The Maximum Non-Reciprocity (MNR) index assumes that Faraday Polarity Shift from Station A to Station B will be identical on the return path, that is from Station B to Station A. Contrary to Spatial Polarity Offset, Faraday Polarity Shift does not "unwind" on the return path. But the question is, in practice, is Faraday Polarity Shift from Station A to Station B really "identical" on the return path from Station B to Station A? The cumulative evidences are overwhelming at this point and they show that more often than we think, it is NOT the case at all. Is this really surprising? Probably not.
Watch this video for instance of a Non-Reciprocal QSO I made with VE1KG (Serge). The MNR index was showing a Maximum Non-Reciprocity of only 1.6 dB. However, considering the outstanding signal from Serge and the relative ERP of our respective stations, it is very clear that the "true" Non-Reciprocity was much much higher than what MNR was suggesting! In fact, a 55 degrees polarity offset between TX and RX was needed in order to enable the QSO between us.
Serge has an excellent station with a 4X17H array. His transmissions were almost all audible despite a strong birdy which was in the way. See his antenna array on the picture to the right.
Another example of this phenomenon is shown in "Section 7", where despite a very low MNR index (0.7 dB), I had to decouple and set a polarity offset of 90 degrees between RX and TX in order to enable a QSO with G4SWX! The collected evidences are overwhelming, and indicate that "MNR" is NOT an absolute measure of the "true effective" Maximum Non-Reciprocity in Earth-Moon-Earth communications.
This finding is very troubling and consequential where this leads us to ask a fundamental question:
How often Non-Reciprocity is much more severe than what MNR is suggesting, and the inability to make an EME QSO is blamed on "high degrade", "poor conditions today" or simply concluding that the station on the other side has "bad ears"...? May be this phenomenon is much more widespread than originally thought!
 Stay tuned...
***WARNING: For Best Resolution for the videos below, it is critical to select 720p HD resolution in the youtube "settings" at bottom right of the player. The 360p default setting won't yield good enough resolution to see the details. It will take several seconds before the High Resolution kicks in, so you will need to restart the video from the beginning when the High Resolution is active and select to view the video in "Full Screen Mode" for best experience...***