What is the relationship between MSE, XPI y Defective Blocks

Hello friends,
I’m aligning two spokes and but I have different values in MSE, XPI.
I was wondering, what is the role of MSE, XPI and Defective Blocks. What does each one measure?

Hello Mack,
Looks like this is an IP20C? I see that radio 1 is 30dB lower than radio 2. In IP20C/PTP820C radio 1 is H-pol and radio 2 is V-pol when interfacing to an OMT kit that then connects to a direct mount antenna. Since the radios are 30dB apart this indicates that you’re interfacing the dual core radio to a single-pol interface on the dish. This is especially true since dishes are V-pol by default and your H-pol radio, radio 1, is the one that is 30dB lower. You will have to replace the rectangular flange that ships with the dish with the dish manufacturer specific OMT interface.

To answer your question about MSE, XPI, and defective blocks, MSE is the Mean Square Error, which is basically a measure of signal quality in log scale. The closer the symbols are to where they’re supposed to arrive in signal space, the smaller the measured delta, which is a good thing. A small number less than 1 converted to log scale will be a large negative number. -42dB is the optimal MSE. In the field you should shoot for around -40dB.

The XPI is the cross-pol isolation, or the difference between the signal strength of the two signals on the V and H polarizations that are sharing the same frequency on an XPIC link.

You can find more detailed information in the user guide as well.


Hello Cambium_Brian,
thanks for taking the time to reply.
Yes, it is an IP20C radio.
For aligning two PTPs, the MSE was observed and the XPI is greater than 25 and less than 30 with a range of (+/- 3). Until now the MSE was not clear to me, but I see that it measures the quality of the signal and apparently after reading other answers, I understand that when you have a bad MSE it is due to interference and/or modulation problems.

What I still have doubts about is the XPI, what is its role in a link and why do they not accept a value (>30dB).

Thanks for your comments.

Hi Mack,
XPI is Cross-Polarization Isolation and cross-pol signals are typically about 30dB isolated from each other in the real world when the same frequency is reused in XPIC setups like what you have.

If you’ve aligned your link well and done a good job of adusting the OMT and radio setup to isolate the V and H signals then when you mute one radio core you should see self-interference from the other radio core at a signal of 30dB lower. If your V-pol signal is arriving at -35dBm for example, when the H-pol is muted your H-pol RSL should be about -65dBm and vice versa.

If you have greater than 30dB XPI that is typically due to transmit levels being different between the polarizations. If your V-pol is transmitting 10dB higher than your H-pol at one end then at the other end you’ll see a 40dB XPI on the V-pol and 20dB XPI for the H-pol signal.

Hope that makes sense. There’s good info on XPI adjustment in the user guide.