At 07:30 AM 4/6/2006, Bill wrote:
>Tor N4OGW Stated
>"Also note that the phasing for the cardioid array shown in that
>report is incorrect. You can't just add a "delay" line of 1/4 wavelength
>to get 90 degree phasing." and
>"Two verticals, 1/4 wave spacing, 90 degrees out of phase."
>withour any explanaiton.
>Please explain Tor. It has worked for me.
There's some examples of this in the ARRL antenna book, with lots of
examples of what kind of pattern you get with "causually designed feed
networks". Forward gain isn't much affected, but the depth of the null is.
If you have two verticals a quarter wave apart, and you feed one with a
transmission line that is 90 degrees longer than the other, you *might* get
the right relative current phases and magnitudes and you might not. The
antennas are close enough that the mutual impedance is almost as big as the
self impedance. There IS a cookbook length for quarter wave spaced
verticals that achieves the right phasing and magnitudes called the
Christman phasing. Using 50 ohm feedlines, one antenna gets a 84 degree
long line and the other gets a 161 degree long line, they're joined at a
T. However, I suspect that if your antennas are non-ideal, it might not
work as well. For instance, if the loss is higher, the effect of the
mutual coupling is less.
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