[TowerTalk] Fwd: Stacking question - another reality data point

[Joe Subich, W4TV]

EZNEC using "real ground" says such a phasing system is not worth
the time/effort.  Remember, the ground reflection is always out of
phase with the "real" antenna so any phase difference one applies
to the higher antennas in the stack is offset by the opposite phase
from the ground reflections.

With HF stacks we're talking about "low" heights - typically less
than 5 wavelengths at most on 10 meters and less than three wave-
lengths (200 feet) on 20 meters.  The answer might be different if
one were considering a stack of 2 meter antennas with the lowest one
at 120 feet (10 wavelengths) above ground - in that case the antennas
would behave more like antennas in "free space."

Lawson's (W2PV) work included attempts to optimize RF at preferred
take off angles by physically tilting the boom of HF antennas.  His
results mirrored that of attempting to do "beam steering" - there
was little difference in elevation pattern with small amounts of
tilt (up to 30 degrees or so) with larger amounts of tilt the peak
gain fell off significantly and the nulls became less pronounced.

In general, with stacks of two or four antennas one can achieve the
maximum practical benefit by simply running one (for a pair) or two
(for four) antennas out of phase.  Try modeling four 24' to 36' boom
6 or 10 meter yagis at 1, 2, 3, 4 wavelengths (evenly spaced) above
ground with all in phase, top two out of phase, middle two out of
phase and 1st/3rd antenna out of phase to see what I'm talking about.

73,

   ... Joe, W4TV


On 8/11/2016 11:48 AM, Hans Hammarquist via TowerTalk wrote:
>
> I have had an idea for some time: When you feed all these stacked
> antennas in phase you will have optimum radiation to the horizon (or
> just above). My idea is to add switchable delay lines to the higher
> located antennas. (You could rather easily replace the damping
> networks in an attenuator with some coax do make this.) Thereby you
> will be able to get optimum angle for "higher up" propagation. You
> should select the steps to be small enough not to get "gaps".
>
> Any taker? (K1TTT?)
>
> Hans - N2JFS
>
>