[TowerTalk] Ground level and sea level

Lee Buller k0wa at swbell.net
Fri Jul 8 14:38:46 EDT 2005


Back in the 80s when I was in broadcasting, the FCC
always looked at height above sea level...even in
Kansas.  The FAA seems to be very interested in ASL
also. (Something about NOT fly planes into mountains) 
I think that surveyors use ASL as a constant that
works anywhere on earth.  That way, the FCC (or
anyone) can then calculate Height Above Averate
Terrain or HAAT.  HAAT seems a little more interesting
to me because it reflects or describes the actual area
of your tower or antenna.  HAAT is calculated on
several radials from the tower and then an average is
taken.  At Kansas State University, KSDB (student run
radio station) had at HAAT for -38 feet.  Yep, they
were broadcasting in a hole or a bowl.  Coupled with a
100 watts and 600 feet of 1" hardline...we could get
out to the city limits of Manhattan.  I moved the
station to a 200 foot tower outside of town on a high
bluff.  One side of the tower was 350 feet above
average terain...but on the south side of the tower
the average was 105 feet.  I cannot remember how many
radials I had to run, but I think it was 8 or more 
Mahattan is located in a river valley (not all of
Kansas is flat either and 14% is forest land as well).
 So, knowing the ASL of a given point then you can do
the simple math of finding HAAT...which I think
matters more...especially on VHF/UHF....and maybe HF.

Your mileage may vary

Lee - K0WA


Common sense is in short supply - get some and use it.
If you can't find any common sense, ask for help from 
somebody that has some common sense. - Lee Buller


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