PTP 800 Link Bounce

I've got a PTP800 link on the 11Ghz band at about 3 miles that has ben stable for the past 5 years.

Now the link is bouncing (link loss while it shifts QAM settings). Both ends were set to 256QAM.

Now, to get the link to stop bouncing I need to set one end to limit at 128QAM or the other link at 64QAM.

If I configure Unit A to 256QAM and Unit B to 128QAM, both units settle on 128QAM.

If I configure Unit A to 64QAM and Unit B to 256QAM, that is what I get.

If I configure Unit A to 128QAM and Unit B to 256QAM, It starts bouncing and is unuseable.

I suspect there is an issue with Unit B, but I have no idea where to look or how to resolve.

Any Ideas?

Is there an Alarm in the home page of the radios? When you click on it, does it indicate an error? I suggest to look at the diagnostic plots for Vector Error, Receive Power and Link Loss. This will give you an idea of the RF conditions. In 5 years things can change like an increase presence of RF interference, path obstructions, etc. Also look at the detailed counters to see packet drop count on RF and Ethernet.

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