I have a 6GHz 820 1+0 link with lpp predicted -47 and actual -50 on both ends. Problem I am experiencing is that when I’m in adaptive mode one side of my link is defaulting to the lowest modulation. The MSE on the higher tx mod side (512QAM) is -36, but on the lower (8psk) it’s -17. I am assuming that the -17db MSE is the reason for the low mod setting but can’t understand 1. why it’s low, and 2. why is -17 worse than -36? Seems to me that a number closer to 0 on the MSE would be better but I’m no expert.
Check your alignment, the MSE should be near identical on each end.
Make sure your using the correct diplexer on each radio.
Check your licenses, make sure they are installed on the correct radio.
Make sure your ATPC is set correctly on both ends.
Alignment is good. They should have used larger dishes but for what we have it matches linkplanner within 3db.
Wouldn’t an incorrect diplexer reveal itself in the RSL?
Have checked licenses and they are clear.
I have ATPC disabled. I don’t know enough about this setting to understand how it would affect adaptive modulation.
Thank you
MSE is kind of like SNR. You want your MSE in the 25-40dB range and ideally same on both sides 30dB is pretty typical for us… if it’s between 40 or higher it means that you have poor signal and at 90, no signal lock. MSE lower then 25dB means you’re experiencing interference. That would explain why the side with -17dB MSE’s modulation is so poor.
You should work with a frequency coordinator and try to find another channel you can temporarily test on. If that channel works well, good modulation, and MSE is back to normal, then make the changes permanent with your coordinator.
That’s a good point for finding another channel to rule out interference. That’s been my gut as the MSE seems to move from 17 to 20ish and for some reason gets better in the rain. 
ATPC is notbdirectly related to modulation but can affect it.
What thisbsetting does is tells the slave end to set its tx power so that the master end does not receive the slave tx singal any stronger than the configured value.
This has the benefit of ensuring that the salve is not running full power if it does not need to and that any rain fade will cause the radio to automatically increase power to maintain that signal level.
This is where it affects modulation since signal level plays a part in how high of modulation rate the radio will go, if you set the atpc setting to -70 but a modulation wont work until -68 then the radio will not go to that modulation.
Thanks for the explanation on ATPC. What are your thoughts on potentially a wrong diplexer causing low RME values? Seems to me a wrong diplexer would distort signal as well, not just RME?
Having a wrong diplexer may not distort your signal, but it will a attenuate it in odd ways. The purpose of the diplexer is not just to combine the two radio paths but it also provide frequency rejection by way of tuned cavity filters. This is why they come high-low and low-high. You can also have the wrong diplexer by frequency as there are multiple sub bands to a given band.