[TowerTalk] TowerTalk Digest, Vol 50, Issue 56
jayt at arraysolutions.com
Sat Feb 24 09:43:09 EST 2007
The best way to answer these questions is to get a copy of HFTA,
which comes with the ARRL Antenna book. It lets you model the pattern
of stacked antennas, varying spacing, etc., and factoring in your
terrain, as well. You just select the kind of antenna (e.g. 5
element beam), and the heights and frequencies, and it plots out
patterns (using generic patterns based on nominal performing antennas).
Unless Dean Straw has changed HFTA it doesn't stack the antenna
correctly. It alway assumes max stack gain. It's purpose is primarily
for take off angle estimates.
So you should model the stack first over flat ground in NSI or EZNEC, or
whatever NEC software you like.
I guess onl AO Wires will do a good job too, and then adjust the hights
to your satisifaction over ground.
A wise man W2PV gave us the stacking formuala years ago.
Optimum stacking distance in Wave Length is the SQ Root of boom length
in Wave Lenths.
So a 1 WL long antenna will stack just fine at 1 WL.
A .5 WL long antenna will be fine at .7 WL
Regards to all
972 203 2008
Military Communications Systems, Phased Arrays, RF Switches, Antennas & Towers
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