russ wrote:
>Hey every one,
>Let us not forget that they change the spacing to get down till on the DB-224.
>
Wrong.
The only way to get downtilt on a binary fed exposed dipole array is to
either build the phasing harness so the electrical length feeding each
element is slightly longer in phase with respect to the one next to it,
or mechanically tilt the array if it is a cardiod pattern. Varying
spacing between elements has little effect on the vertical beam pattern.
There is very little difference in the performance of a dipole array
with varying amounts of spacing between the elements. Most
manufacturers shoot for about 80 to 90% of a full wavelength between
elements, but the spacing is really not that critical. Also, the amount
of pipe above the top element is not critical as long as there is enough
to maintain the impedance of that element. It could be 2 inches or 2
feet, as long as the match is okay it doesn't matter.
The spacing of the element from the mast (reflector) affects impedance
greatly. Don't try to mount your Cushcraft AFM-4DA or 44DA on a
fiberglass or plastic mast pipe. It won't work....
Kevin Custer
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