[TowerTalk] [CQ-Contest] Stacking on separate towers, take off angles?

[Jim Lux]

On 3/16/13 7:55 AM, Jim Brown wrote:
> On 3/15/2013 8:19 PM, David Gilbert wrote:
>> No way that the respective wavefronts will add in all of those
>> directions.  Geometry alone would tell you they are much more likely
>> to cancel in some directions.
>
> Yes, we can drive two or three Yagis pointed in the same or different
> directions, but HOW they combine to form a pattern can be as close to
> the infinite number of monkeys and typewriters as it is to how the
> operator thinks he is aiming them.
> \

when you start spacing at more than a wavelength, you're really building 
an interferometer, so you'll get some interesting combination of grating 
lobes and the element patterns.

There are some generally useful cases, though.. two fairly high gain 
antennas pointed in fairly different directions.  There's not much 
interferometer/grating lobe effect because in the main lobe direction of 
antenna A, the fields from antenna B are small.   So want you get is 
something with two big lobes and a lot of little stuff.

Maybe you're in a geographic location and you want to set up HF links to 
two other places and don't want to have to worry about switching 
antennas, etc.

A similar use case at VHF is where you have two big cities  that are 
90-100 degrees apart from your distant location, and you want OTA TV. 
Two fixed LPDAs one pointed at each city and a power combiner and you're 
good to go.   Say, if you were in Orange County  and wanted to receive 
the Los Angles and San Diego stations.  (in this case, the "LA" antenna 
could probably be a piece of wire or the back lobes of your SD facing 
LPDA, though)