[TowerTalk] Site Elevation and TOA

[Bill via TowerTalk]

According to N6BV, who knows his stuff...
 
Beyond approximately14000 feet has very little effect on the TOA  for HF.  
Close in is far more important.  You can test this by making  up a file with 
hypothetical elevations and putting it into N6BV's  program
 
Bill K4XS

 
 
In a message dated 6/17/2014 9:47:04 P.M. Coordinated Universal Time,  
w9ac at arrl.net writes:

I'm  trying to locate land in south GA for a remote Internet station.  Two  
self-supporting towers are ready for installation.  Tower #1 is 140 ft  and 
Tower #2 is 100 ft.  A full-size, 4L 40m monoband Yagi goes on the  top of 
tower #1.  A 30m-10m LPDA goes on tower #2.  Siting has  become a lot harder 
than I imagined.  Here are my siting  constraints:

1) Low noise in the immediate area;
2) Easy utility  power access;
3) High speed data access over FTTH or CATV.  No DSL  unless I really get 
desperate.  Too many future applications will need  the extra throughput;
4) High land that either remains flat for the TOA  distance or slopes 
downward.  
5) Land that fits within the project  budget.

Sounds easy. Way harder than you think -- unless a home goes up  on the 
property and I move there where I have more options due to the higher  price of 
properties.  Moreover, many counties won't allow a telecom  shelter or 
other structure as a primary use without first establishing a  residence through 
placement a house or manufactured home.  I don't want  that.  I want a 
remote site only.  My main focus is Brantley County,  GA.  There's no zoning in 
the county.  There's also super-high-speed  fiber supplied to the entire 
rural county by the local telco.  The telco  bet big and lost when they assumed 
a housing market explosion in 2005 that  turned into an implosion.  Along 
the county highways are dozens of  started subdivisions that are now ghost 
towns.  Cheap land, but the  developers recorded much of it early on with deed 
restrictions.  Once  just a few owners take possession, changing the 
covenants is a  nightmare.  It's one thing to take up the cause when you already 
own the  land.  It
's insane to consider restricted land when you're looking to  buy from the 
start.   

After looking at dozens of parcels,  I've found a few that might work.  
Here's my question: In terms of  wavelength, at what distance is the TOA set 
for elevated, horizontal  antennas?  I realize that the TOA is composed of 
near, intermediate and  far fields above elevation, but there must be a 
distance where say...90% of  the predicted TOA occurs.  What is that distance in 
wavelengths from the  antenna?

Paul,  W9AC
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