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 To: [email protected] 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
