It's 11 Dec 96  19:40,
We'll return to Richard Trostel and Wayne Sarosi's
discussion of [LOW BUDGET ANTENNAS-
 RT> Would a beam provide enough gain to make the desired signal strong
 RT> enough to override the interference?  Is the RS antenna sensative
 RT> enough for the job? It seams to be built on a log periodic principle.
 RT> Would it be better to build a beam with alot of gain that is designed
 RT> for the  Frequency intrested in?
You might be able to phase a couple of antennas, so that the unwanted
station is nulled out (i.e. design the pattern so that a deep null
appears in that direction).  This could be done with a pair of co-phased
beams, spaced so that they are 1/2 wavelength apart, in the direction of
the interfering signal.
That's a bit hard to draw in ASCII, but a good book should be able to
show the details.  Anyway, here goes. :-)
                          /
                 | | |   / Distance = 0.5 wavelengths between
                 +-+-+  /        antennas, as seen from interfering
                 | | |        /  station.
                             /
                            /                            X (desired
                           /                                station)
                          /
                 | | |   /
                 +-+-+  /
                 | | |
                                   Y (interference)
          Actual spacing will be 1/sin (angle between interference
          and desired station * 1/2 wavelength).
Hope that's right, just did a quick derivation from first principles.
:-)
So, if the interference is at 90 degrees, then the spacing is 1/2
wavelength, if the interference is 45 degrees from the desired station,
then the spacing between the antennas will be 1/2 * 1/sin (45d) *
wavelength, or about 0.7 wavelength. :-)
Of course, it goes without saying that the feedlines used in the phasing
harness need to be exactly the same length for each antenna. :-) ).
... I'm a proud member of Mensa that forgot to renew my membership!
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