Frequencies above 6050MHz not working on C5c

Right now I have 3 PTP links, all of them with C5c radios and in different sites. But with none of them I am able to use higher frequencies. The higher I go from 6050MHz the higher the signal goes and also modulation and data rate drops. Usually signal would go from -60 to -65+ dBm. Also PER went 6%+. You can see in the spectrum that all those frequencies are supossed to be noise free but I can’t get to use any of these frequencies in any of my links.
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I would suspect your antenna to be at fault. Most of the time the antenna performance is going to change drastically even inside of the frequencies it is certified for. This can be far worse for frequencies outside of the antennas original design specifications.