Far from Omni!


#1

Hi Folks, just a little confused that when I rotate my Flightaware 26" antenna my coverage area changes quite dramatically, although it is clearly a Omni design. Any thoughts as to why?


#2

It does not make sense, but I wonder if I’m experiencing the same thing. Minor changes, like turning it around, or slanting it a bit, result in big differences. I thought it was due to the fact that my antenna is indoors. I’ll pay more attention from now on.


#3

i think it does (have witnessed it often) specially if its is slightly tilted towards the furthest point on the horizon with the most traffic, due to the lobes (seen in graphs).
as most of the signal is received around 90° and 270°. if the earth was flat wouldn’t be a problem but…and by tilting it, becomes short of ‘directional’ and not omni.


#4

OK, thanks - back up the ladder this weekend … this time with a spirit level!


#5

What do you consider “slightly” when you say " … if it’s slightly tilted towards the furthest point … " ??


#6

In my case it’s currently tilted around 30 degrees towards the house. I should try tilting it in the opposite direction, towards the air traffic, and see what happens.


#7

If the antenna is just slightly not vertical, it can have large effect of the reception - will favor one direction (where the directivity lobes are in the air) while un-favouring other (where lobes are pointing in the ground).
abcd567 did some simulations about those lobes.


#8

5°-10° max, towards the desired direction.

did not touch gain ( is set at 29.7).

tilted%20cantenna

with at least 3 comm towers within 300m and 1 radar site (old ATH airport) within 2km.