You'll find the site here.
These figures assume a basically horizontal path across the earth and are in addition to the normal free space path loss (which you have to add on). The gas loss figures are directly proportional to the distance. i.e. for a 10km path just divide the figure by 10.
Today I've added another page to the site that will calculate the total path loss based on the weather condition you enter. Additionally, if you enter the TX power, and the TX & RX antenna gains, it will calculate the received signal strength.
This calculator accessible using the 'CALC' link at the top-right of the web page.
Note: There is very little checking for 'silly' input data.
If you manage to crash it can you please let me know how you did it.
