[TowerTalk] Take-off angles & Modelling Tri-Banders

[Andy Cook, G4PIQ]

Firstly, thanks to those of you who pointed me in the right direction
when I was looking for take-off angle data some months ago. The data
certainly is there inside the VOACAP reports, although from looking at
the coverage maps, the model does seem to generate dead zones which I
suspect don't actually exist. It looks like the model is only
considering the dominant mode as contributing to the field strength at
any point, and it looks as if you get strangly located and very narrow
'dead zones' around the boundaries between one mode and the next higher
order mode kicking in. 

I was originally asking for statistical data on how the arival angles
change form day to day over a particular path. I still don't feel that I
have that data, but maybe the question is wrong and what we really have
is differing dominant modes from one day to another.

However - what I was really trying to tap the collective towertalk
consciousness for this time is whether there are any EZNEC models
kicking about for common tri-banders. I can see that it should be
possible to develop them, but it may not be an easy task. I'm
particularly interested in the KT34-XA, TH5 and A3.

If proper models for these antennas aren't easy, what would you
recommend doing when trying to match take-off angles with propagation. I
guess running with a monobander of similar boom length and height would
be a good start.

Comments anyone.

73,

Andy Cook, G4PIQ
g4piq@blacksheep.org

Oh yes - hope to work a few of you in WPX SSB in a fairly casual MS
effort as M8T.

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