ITU rain regions
rain outage by region
rain attenuation table
A very critical 60Ghz link failed this week due to moderate rain even though vendor techie had "guaranteed" this would never happen based on their in-house calculator.
Vendors use 1970s ITU region charts for predicting how many minutes per year a link could be down in a particular region. El-Nino, global warming, etc has changed the picture a bit.
Needless to say I told the IT guy "I told you" a few times as I predicted this would happen on many rainy days based on this simple chart by ITU/IEEE.
But it is quite easy to do your own due dilligence before spending $$$$$ on a link.
1. Ask vendor to provide realistic SNR margin requirement for highest throughput totally ignoring rain fade
assuming you will deploy in the Sahara desert.
2. Ask if radio automatically adjusts speed as bit-error rates increase or decrease, and the SNR required for each of the lower speeds - again assuming Sahara deployment.
3. The numbers could be like 6dB for QPSK, 12dB for QAM16, 18dB for QAM64 and 24dB for QAM256, etc. You can be more conservative by adding 3dB.
4. Calculate "dry" link margins using as accurate radio and antenna specs as you can get from vendor.
5. Now look up the dB attenuation in various types of rain for your radio's operating frequency from the bottom chart. Multiply by link distance and subtract from "dry" link margin to calculate "wet" link margin - hopefully it is a positive number.