Hi to all,
I have 65km 5.8 GHz link between two cities. Each side has 32dbi parabolic antenna, 532A, Compex miniPCI 200mW. Thats all works fine at ~ -65-70dbm but sometimes i have very large floating of signal. It happends that link works fine for 5 days at -65 and than start to going down to -80, -90 and in the end, completly losing signal. After few minutes, things came back to normal and everything working ok. Sometimes need to pass even half an hour and more to things came back to normal. All this happends no matter what the weather is, tempeature, preasure, time of day and i couldn't find any reason for this. Terrain between towers is mostly fields and some small forest.
Also, signal strength sometimes goes up to -55 (?!). What is the explanation for this floating and how can i fix this? Polarization is vertical, is it better to use horizontal for long link? Antennas on each side are well fixed.

As far as the polarization goes, its not a matter** of which is best but rather which is less prone to interference... More than 90% of wifi equipment and other manfucturers utilize vertical polarization in their antenna design. Experimentation or a spectrum any. is the only way your gonna find out which polarization is "better". My guess is that you are experiencing some noise in your band. Suggestion: Switch the polarities of both antennae to hori. and that shud help... if it doesn't then check pigtail/cable/connector configuration as these problems are quite common, and also the 5.8 band is not so forgiving when it comes to cable errors


Regards

IMHO it is another issue, require space diversity actual for 5Ghz links (but not very for 2.* ghz).
It means depends on weather conditions possible path of signal changes.
But this is just an idea.