"Reg Edwards" wrote in message
...
The two antennas behave as one, [...snip...]


How come no one told me what an SEM is??

There will be one null only if there is one noise
source.

Reg explains well, but I don't believe this item is, in general, true.
One example case could be two identical verticals where you wind up with
them fed 180 degrees out from each other. There will be two nulls broadside
to the antenna and 180 out, in direction, from each other (an Adcock).
Change the phase and both nulls tilt toward the direction of one antenna or
the other...untill they coencide and you have the cardioid.
With at least one directional antenna, the "other null" may be where
there is little pickup from the directional antenna and therefore non equal
signals and the "noise sense" antenna signal would dominate, in essence
hurting the directivity of the "main" antenna. (Because there isn't enough
from the main antenna to cancel what comes from the noise antenna.) Ya
gotta have both to cancel.
Therefore, it's a bit more complex as well, but killing the noise may
far outweigh other problems. But as Reg says, you want to maximize the
niose pickup in the noise antenna and minimize the desired signal in the
noise antenna.

Automatic systems like this are used on "radio gun ships" Lotsa radios
trying to interfere with each other. Sample the offending transmitter at
its output and cancel it at the problem receiver.


--
Steve N, K,9;d, c. i My email has no u's.