[TowerTalk] ridge top derating factors

[Bill Coleman AA4LR]

On 4/13/00 4:13 PM, John Langdon at jlangdon@outer.net wrote:

>Just an unscientific observation, but I am on a not very high ridge, but I
>have seen the antennas on the tower (at various heights up to 195')
>deflecting in two different directions from each other and both different
>from what the prevailing winds were on the ground,

Not unscientific at all. In the aviation world, we call that "wind 
shear". It's layers of air moving in different directions.

> and I have also started
>up the tower in relative calm at the ground level and decided not to work
>because the winds were too much at 90', and found it still calm when I got
>back down to the base of the tower again. Never boring!

Contact with the ground causes the air close to the ground to move more 
slowly, due to friction. It's not unsual to have a considerable gradient 
of wind speeds in the first 200 feet.

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@radio.org
Quote: "Boot, you transistorized tormentor! Boot!"
            -- Archibald Asparagus, VeggieTales


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