[TowerTalk] Non-vertical stacking question

[Jim Lux]

At 12:33 PM 7/6/2004 -0400, TexasRF at aol.com wrote:
>Regarding Bill's non-vertical stacking question:
>
>In the directions that the antenas deliver in phase signals to the combining
>device, the stacking gain should be there and normal. In the directions the
>signals are out of phase, there wil be a null. In between directions will 
>give
>in between results as well.
>
>This would be a great application to use one of the variable delay line units
>to vary the phase of one of the antennas to allow proper in phase combining.
>There was an ARRL Antenna Compendium several years ago, authored by W5AH on
>such a unit to be used with two vertical antennas. The unit used several 
>relays
>to switch different lengths of coax sections in/out to accomplish the 
>variable
>phasing effect.


Switching coax in is all well and good, but if there's any mutual 
interaction between the antennas, then you wind up with weird power 
distributions and unexpected phase shifts, because the impedances at the 
feed points aren't 50 ohms.

The antenna Compendium article that I think you referring to actually used 
a modified antenna tuner as a pi network phase shifter, and I think he had 
the antennas far enough apart that the mutual Z was low.