Hi.
I have a bit of a general MT wireless question. I have run MT gear for a long time(10 Years now!) and have seen this wireless link phenomenon notably in my long distance links(7KM's+), but never understood why this occurs. This is notable when I am passing little to no traffic.
If I have hard set the Band to say 5GHz -ONLY-N on both links, why is it that I see Rx rates drop back to an 'A' mode momentarily and not to say a lower 'N' speed ?

What is on your advanced WiFi configuration data rates? The lower rates are to reduce power usage and minimal control (beacon, etc).
If you want always high transfer rates, you need to disable the lower data rates manually, at the cost of stability considering the signal quality and noise.

Rates will always drop to lowest, if there is no need for higher rate (if there is no traffic). This is also to save power. If you will have traffic, it will auto adjust to highest.