Kevin is quite correct. Tis the phasing harness construction that determines downtilt of a corporate feed antenna (or physical tilt of the antenna).
Chuck WB2EDV ----- Original Message ----- From: "Kevin Custer" <[EMAIL PROTECTED]> To: <Repeater-Builder@yahoogroups.com> Sent: Monday, January 24, 2005 5:46 PM Subject: Re: [Repeater-Builder] Re: DB224 "Loop" Lengths for 145.110 Mhz? > > 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 > Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/