On Saturday, February 2, 2013 6:10:44 PM UTC-6, Jeff Liebermann wrote:
I'm often impressed with the ability of some antennas (mostly

mobile antennas) to send most of the RF towards the sky, while leaving

little towards the horizon. However, that shouldn't matter here,

where a hemispherical pattern, that covers the entire sky, is the

goal. Maybe a discone?

Dunno.. I've done a lot of air band listening, and myself, I
think it's best to concentrate of the tower, and letting the
airborne chips fall as they may. Unless one is real close to
the airport, the tower, ATIS, and other ground signals will
usually be the toughest to hear.
The idea of using a *short* yagi actually works quite well in
most cases. You can hear the ground stations, and still most
of the others in the air also. Most of the airborne signals
will be fairly stout, and a rubber ducky would pick them up.
The more gain the yagi has, and the tighter the pattern,
the better the tower, but the worse the airborne.
This is why I would stick with short 2-3 el yagi's if going
that route. You don't want too much gain.

I've got a simple 3 el yagi cut for 2m, and I'd often use
it for air band. I could tweak the direction for best tower
signals, and with the antenna out of tune, the pattern is
not sharp, and would pick up most everything well enough.

Using that, I could receive ACARS from cruising jets up to
about 300 miles. From Houston, to about the OK border or so..
I could follow Southwest jets from KHOU to KDAL, and I could
hear them going into Dallas until they descended to about 9000
feet or so. And that's with the 2m yagi in no particular direction,
or aimed to favor Hobby.. With an out of tune yagi, sometimes
the max signal does not jive with the normal direction..

Anyway, I've found that it's best to favor the ground signals,
and not worry much about airborne. You will hear those with
little trouble. And this is the main reason I take the
decoupling into consideration if using a simple vertical.
You will want good decoupling to do well on the low angle
ground signals. A sky warmer will not be your friend in this
case.