Milt, You gave an excellent description of the problem, and I agree that a lower gain antenna is called for. However, there is a "dirty little secret" regarding fiberglass vertical antennas with electrical downtilt: Their vertical patterns are quite "spoky," meaning that there are many peaks and nulls. For example, one of the local radio clubs has a Celwave Super Stationmaster antenna with electrical downtilt on a nearby mountaintop repeater. The downtilt was chosen in good faith to provide close-in coverage of users living near the base of the mountain. Over time, we found that there were many areas where you had line-of-sight to the repeater but could not get into it from a handheld. But, you could move closer or further away and then get in, full-quieting. This phenomenon was repeated at intervals.
Bottom line: Electrical downtilt is not as simple as it sounds, and it should be employed only after careful study of the antenna radiation patterns and the desired coverage areas. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of men...@pa.net Sent: Saturday, October 10, 2009 6:20 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: feeding two 120 degree sector antennas If i read your post correctly, you are trying to achieve omni coverage and downtilt while maintaining a high level of antenna gain. I think that you will only achieve what you want by using electrical downtilting in the antenna. Otherwise you are going to have to trade off something. I might try using a lower gain omni antenna since the concept of antenna gain is basically "squashing the doughnut" (if you have seen the illustration of a doughnut on it's side as representative of the pattern of the antenna radiation pattern for an omni antenna) in that as antenna gain increases, vertical beamwidth decreases. Try a 6dB or 3dB omni (if available for your frequency range) and see if that improves the closer coverage. It might also have the benefit of reducing interference from distant stations. In re-reading you original post I see that you have 2-120 degree sector antennas spaced 60 degrees apart. While this is an area that I don't have practical experience in, I recall that overlapping antenna patterns can be additive or subtractive. I would change the spacing so that the antennas are 120 degrees apart and see if that doesn't improve the overall performance. Milt N3LTQ Quoting Matthew <kc7...@hotmail.com <mailto:kc7eqo%40hotmail.com> >: > I am trying to achieve an almost 360 pattern with some gain and down tilt. > Right now I have a vertical antenna at 11 dBi with no down tilt, so most of > my gain is shot out in the horizon. So the area I am trying to get my > maximum gain is from under my antenna (Red in attached pic) to 7 to 15 miles > out which requires either electrical down tilt of the antenna or a > mechanical one. I drew a very crude picture to show what I am trying to do. > See attached or embedded. > > > > Thanks > > > > 73 > > > > Matthew > > KC7EQO > > > > PS the null is not critical, just trying to focus the energy to the area I > am trying to serve. > > > > > > > > _____ > > From: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > [mailto:Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Barry > Sent: Friday, October 09, 2009 8:04 PM > To: repeater-builder@yahoogroups.com <mailto:repeater-builder%40yahoogroups.com> > Subject: RE: [Repeater-Builder] Re: feeding two 120 degree sector antennas > > > > > > How about some indication of what you hope to achieve > I use a skelol slot I made on .70cm with great success and have used a > refletor with good gain on a vertical in the past for a null > B > > > fyi http://www.patentstorm.us/patents/5477224/claims.html <http://www.patentstorm.us/patents/5477224/claims.html> > > _____ > > To: Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > From: kc7...@hotmail.com <mailto:kc7eqo%40hotmail.com> > Date: Fri, 9 Oct 2009 23:25:31 +0000 > Subject: [Repeater-Builder] Re: feeding two 120 degree sector antennas > > > > LOL thanks for your honesty. I am sure someone here can help with my > questions. > > Oh BTW I have have not slept at a Holiday Inn Express either :) those are > funny and creative commercials too. > > 73 > > Matthew > KC7EQO > > --- In Repeater-Builder@ <mailto:Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > > yahoogroups.com, "Chuck Kelsey" <wb2...@...> wrote: >> >> Actually Jeff Depolo is much better versed to explain this than I am. >> Hopefully he can enter into this thread. I don't have an engineering >> background, and don't play an engineer on TV. I haven't even stayed at a >> Holiday Inn Express :-) >> >> Chuck >> WB2EDV >> >> >> >> ----- Original Message ----- >> From: "Matt" <kc7...@...> >> To: <Repeater-Builder@ <mailto:Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > > yahoogroups.com> >> Sent: Friday, October 09, 2009 6:55 PM >> Subject: [Repeater-Builder] Re: feeding two 120 degree sector antennas >> >> >> > Thanks for replying Chuck. The antennas are not perfectly back to back. >> > More like 60 degrees from each other. >> > >> > I would have thought I'd have a null in one direction. Is there a better > >> > way to do this? >> > >> > I want close to the 11 dB gain my omni has, but with more down tilt. >> > >> > Thanks, >> > >> > 73 >> > >> > Matthew >> > KC7EQO >> > >> > --- In Repeater-Builder@ <mailto:Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > > yahoogroups.com, "Chuck Kelsey" <wb2edv@> >> > wrote: >> >> >> >> Are the two antennas pointed the same direction? If they are back to >> >> back, >> >> I'd guess that your results are what I'd expect. >> >> >> >> Chuck >> >> WB2EDV >> >> >> >> >> >> >> >> ----- Original Message ----- >> >> From: "Matt" <kc7eqo@> >> >> To: <Repeater-Builder@ <mailto:Repeater-Builder@yahoogroups.com <mailto:Repeater-Builder%40yahoogroups.com> > > yahoogroups.com> >> >> Sent: Friday, October 09, 2009 2:29 PM >> >> Subject: [Repeater-Builder] feeding two 120 degree sector antennas >> >> >> >> >> >> >I am experimenting with some 3 Ghz antennas. I have a 2 way power >> >> >divider >> >> >feeding two 120 degree sector antennas rated at 15 dBi each. I have a > 11 >> >> >dBi omni that I am comparing it too. It seems the omni is getting > better >> >> >performance then the array is. I am seeing more than a 4 dB > difference, >> >> >loss. My goal is to get more down tilt in my antenna pattern, as the >> >> >sectors offer a mechanical down tilt. >> >> > >> >> > Am I doing something wrong? >> >> > >> >> > I am feeding the antennas with LMR400 and feed is short as possible. >> >> > Each >> >> > feed from the divider is 15 inches long to the antenna. The insertion > >> >> > loss >> >> > in the divider is <0.4 dBi according to the spec sheet. >> >> > >> >> > Thanks in advance, >> >> > >> >> > Matthew >> >> > >> >> > >> >> > >> >> > ------------------------------------ >> >> > >> >> > >> >> > >> >> > Yahoo! Groups Links >> >> > >> >> > >> >> > >> >> >> > >> > >> > >> > >> > ------------------------------------ >> > >> > >> > >> > Yahoo! Groups Links >> > >> > >> > >> > >> > > > > > > _____ > > Check out The Great Australian Pay Check Take a > <http://clk.atdmt.com/NMN/go/157639755/direct/01/ <http://clk.atdmt.com/NMN/go/157639755/direct/01/> > peek at other people's > pay and perks > > > >
