Modem XPI Delta

Hey folks... we recently installed a PTP820c and noticed that our XPI indicators are very different between the two radios. Any ideas of what this means and if this is a good or bad thing? If bad, how do we correct it? Thanks!


       At 256QAM modulation the min MSE Down Threshold is -30 so your on the cusp of dropping to 128. For the XPI with that big of a delta one end is hearing more noise as we look for a XPI of 25 or greater. Is it the same on the other end of the link as well?

•XPI: Cross Polarization Isolation

–How much Horizontal signal appears on the Vertical receiver?

–How much Vertical signal appears on the Horizontal receiver?

•Confirm with the following procedure:

–Mute far end V transmitter (Tx). The difference between local H’s RSL and local V’s RSL is the XPI.

–For example, with far end V Tx muted, local H’s RSL is -30 dBm, and local V’s RSL is -55 dBm. (-30 – (-55) = 25 dB)

–Un-mute far end V Tx, and mute far end H Tx. The difference between local V’s RSL and local H’s RSL is the XPI.

•With six foot (6 ft) or smaller antennas, maximize XPI by:

–Aligning the antennas for maximum RSL (as per the alignment procedures)

–Slightly twisting one link end’s OMT

–Instead of slightly twisting one link end’s OMT, ensure that both OMTs are level!

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Thanks for the quick reply Justin.

Here's what the other side of the link looks like:

We're using 3' dishes on each side. This is a 12.6mi link. LinkPlanner shows that we should be getting -37dBm +-4dB. We have ATPC set to -55, but even with this off, it doesn't get close to the -37dBm target. So which side do you think is having the problem and we should try adjusting the OMT? Thanks!