Just wondering i am putting a dipole on the roof of a 12 story building
i'll mount it around 30ft off the flat surface of that roof

my antena will be about 150 ft off the sidewalk


when trying to calculate my dipoles hight is it above the roof surface
or 'real' earth /sidewalk ground that 'counts'??

thanks

On Sat, 05 Feb 2005 19:03:47 GMT, ml wrote:

when trying to calculate my dipoles hight is it above the roof surface
or 'real' earth /sidewalk ground that 'counts'??

Hi OM,

If you were on a step ladder putting up the antenna, which would feel
worse if you fell? Hitting the roof or hitting the sidewalk? That is
how much it counts.

Another point of view is if you were to shine a flash light from your
roof, or from the sidewalk, which would offer a greater chance of
being seen a mile away? That is how much it counts.

However, there are complexities beyond these sophisms. How much
chance would your flashlight have being seen if you were obstructed by
a penthouse? Hence there are factors that reduce the effectiveness of
your antenna on the roof. The question is how much - which is a
question everyone has to answer for their own situation. The
difference here is that even if you suffer equally with everyone else,
you still have the advantage of height. So, barring a horrible
situation on the roof, you enjoy a net sum gain.

73's
Richard Clark, KB7QHC

"ml" wrote in message
...
Just wondering i am putting a dipole on the roof of a 12 story building
i'll mount it around 30ft off the flat surface of that roof

my antena will be about 150 ft off the sidewalk


when trying to calculate my dipoles hight is it above the roof surface
or 'real' earth /sidewalk ground that 'counts'??

thanks

===========================

Just take the geometric mean.

Effective Height = Sqrt( 150 * 30 ) = 67 feet.

But what you do with this number hardly matters two hoots. What do you have
in mind to use the number for?

Just continue to do as you intend and I'm sure the antenna will work fine.
It's very few people who have a starting point of 150 feet.
---
Reg.