Hi Guys, Thanks for the info on the 224 - there's not much behind us that we really want to cover, so it's not a big deal.
Since we're putting up a couple of antennas (one of which I have the final say so), I'll humor the old salt on his, & do all 4 straight aligned on mine. :-) Thanks again! Tim --- In Repeater-Builder@yahoogroups.com, Jacob Suter <jsu...@...> wrote: > > Theres a lot to account for in this: > > A> side-mounting on self-standing towers with significant amounts of leg > angle will reduce the 'total blockage' of the antenna in any direction > at one time. As long as one dipole is visable on your antenna you can > still calculate for that one dipole's gain alone. > > B> not all towers are equal. You're going to see a lot more random > reflection/attenuation from a tower thats 'coated' with coax or internal > structure vs one thats practically bare. > > C> offset mounting length can make all the difference in the world. a 4 > ft offset at 927 mhz is significantly more wavelengths than a 4 ft > offset at 2M/220/440. > > D> most towers tend to have less cable hanging on them the farther you > go up (or even switch to a smaller structure...) > > Just a few more things to consider... > > JS > > > > > > Roger White wrote: > > > > > > Our 145.43 MHz repeater has been on a self supporting tower 450 ft. > > high, at the 250 ft. level ( a Stationmaster at first and a dB224 > > later) and now at the 350 ft. level (dB224). The tower face at both > > heights was considerable (well over 20 to 25 ft. wide). The antenna > > was offset from the tower leg a considerable distance in both > > instances and the dipole elements were orientated for a omni > > pattern. My guess is that the tower face is so big where we have had > > the antennas at that the effect off offsetting the dipoles in one > > direction is minor compared to the effect that the large tower face > > would have on the pattern. > > > > As you would expect, the pattern nulls off the backside > > are considerable, but not severe enough to limit communications. The > > higher frequency you go, the less the effect is. We have a 224 MHz > > repeater (dB224JJ set for an omni pattern) at the 300 ft. level and it > > seems to do quite well hearing off the backside. Our 927 MHz repeater > > at 400 feet (using an unused paging antenna) seems to hear off the > > backside almost as well as it does off the front side. > > > > Since beggars can't be choosers, we have over the last 25 years on the > > tower accepted the pattern deficiencies. I can take a few pics if you > > would like to see how they are mounted. > > > > Roger W5RDW > > Murphy, Texas > > DFW area > > > > ----- Original Message ----- > > > > *From:* tahrens301 <mailto:tahr...@...> > > *To:* Repeater-Builder@yahoogroups.com > > <mailto:Repeater-Builder@yahoogroups.com> > > *Sent:* Tuesday, June 30, 2009 2:35 PM > > *Subject:* [Repeater-Builder] DB-224 patterns on side of tower. > > > > Hi Folks, > > > > We are putting up the DB-224 on the side of the tower, > > which is one of those large 3 legged towers. (like you > > see at microwave & telephone sites). > > > > I have the DB-products data sheet on the 224, and it > > has some plots for side mounting on the tower. > > > > The plot in question is the 224E (all in line, pointed > > away from the tower). > > > > According to DBprod, it would give the appropriate pattern > > for our desired area. However, one of the old salts here > > (who has final say-so) says that you really have to put some > > left and right angulation on the elements to get that pattern. > > > > I guess the real question is how positioning on the side of > > the large tower affects the pattern - if the elements are > > directly perpendicular to the tower leg, versus having some > > rotation on the leg. > > > > I'm thinking that we will probably just have to experiment > > with what we get per old-salt's method & see how it works. > > > > Anybody have any other ideas? > > > > Thanks, > > > > Tim W5FN > > > > >
