North Queens TV White Space Trials
These trials where started in early October at a time when the trees still had most of their leafs, we went back and retested some of the links 6 weeks later after nearly all the leafs had fallen.
The average 5km link saw an increase in signal strength of 5-7dBi with the results being dependent on the types of trees and amount of free space in the signal path, we have marked the tests that have had this 2nd round of testing with an * on the test site 2 results page.
A bigger surprise has come with the early results of our long term tests, these where started in early December long after all the leafs where gone and we didn't expect much variation in signal strength, we were wrong.
Over a one week period we have seen a variation in signal strength of 12dBm over a 9km link fortunately higher than our initial test. The weather has been a significant factor we have seen the following conditions
Cold -15C windy blizzard conditions signal -70dBm
Heavy snow fall no wind -5C signal -78dBm this increased to -74dBm after a wind came up
Calm high humidity and rain, temperature around freezing, signal -82dBm
Rain windy humidity 97% +12C signal -81dBm
Our current theory is that unlike conventional links where most of the signal path is through free space a lot of the signal path is through vegetation specifically evergreen trees. As the illustration below shows a significant part of the signal path is skimming through the tree tops where a build up of snow or moisture would have a noticeable affect.
During rainy humid weather we have a combination of higher free space loss and greater attenuation in the trees.
The signal path showing how over 1/2 the signal path is through the tree tops.
This turned out to be one of the links which for it's length had one of the smallest changes in signal path loss when the leafs returned only 3-4dBm. It would appear the satellite data is correct and most of the signal path is through or just above the trees which are mainly evergreen.
This is certainly an effect an installer would want to be aware of when deciding if a location had sufficient signal for a permanent installation