[TowerTalk] 2 element quad on a 17.5' roof tower?

[Jim Brown]

On Wed, 21 Apr 2010 00:34:02 -0700, Jon Knodel wrote:

> My question is, how much interaction with the roof will I have and how 
>much will it degrade performance with the bottom of the loops being so 
>close to the roof?  I figure the bottom of the 20m loop will be roughly 
>8' above the roof.  The house is typical wood construction with asphalt 
>shingle roofing.

There should be no interaction with this sort of construction unless there 
are some conductive elements in it that are close to a half wavelength (or 
multiples). If you don't live in "flatland", in addition to NEC, it is also 
worth using HFTA to study how your planned mounting height will work with the 
terrain. HFTA is written by N6BV, and is distributed free with the ARRL 
Antenna Book. Many of us in N California have used it and found to be be a 
very good predictor of the performance of horizontally polarized antennas. 

73,

Jim K9YC