[TowerTalk] How High is enough

[David Gilbert]

Not only are the optimum takeoff/arrival angles that are built into the 
"Figure of Merit" calculation in HFTA based upon averages, they are 
based upon monthly averages computed from VOACAP over an entire 11 year 
sunspot cycle.  On top of that, one of the original contributors to 
VOACAP (I believe it was George Lane) has pointed out that of all the 20 
or so parameters that VOACAP can address (signal strength, SNR, path 
loss, etc), TANGLE (optimum takeoff angle) and RANGLE (optimum receive 
angle) have the least rigorous data to substantiate them.  I love HFTA 
and I think it does a pretty fine job of computing takeoff angles over 
varied terrain, but I take the optimum angle figures with a grain of salt.

Besides, as you say, the optimum angle at any moment is dependent upon 
many factors.  Generally speaking, very low angles will do a better job 
when the band is opening/closing, but often have less of an advantage 
(and for some paths even a disadvantage) during the midpoint of an 
opening.  Also, long path openings that depend upon gray line chordal 
hop propagation can sometimes do just fine with surprisingly high 
takeoff angles.

In general it's tough to beat raw height, but as you and others here 
have said ... it all depends.

73,
Dave   AB7E


On 7/31/2013 5:32 PM, Rick Kiessig wrote:


Regarding HFTA, while I think it's a wonderful tool, be aware that the
arrival angles it uses are based on VOACAP, which means they are averages
only. There will be (many) times when those numbers don't apply -- which is
another reason some flexibility is ideal.


73, Rick ZL2HAM (ZM1G/ZL1G)