Doug - Do you know how the phasing harness was constructed for the three-element version? I don't, and that's why I suggested to Norm that he go with four - the phasing harness is easy.
Or, he could use two elements for transmit and one for receive. I don't know how much isolation he'll need, but he might just get away without a duplexer if there's enough tower. Chuck WB2EDV ----- Original Message ----- From: "Doug Rehman" <[email protected]> To: <[email protected]> Sent: Monday, August 30, 2010 2:28 PM Subject: RE: [Repeater-Builder] DB212-3 > In a previous life I managed the communications for a state police agency. > We used 45 MHz for our main system and had forty some odd tower sites, > almost all running DB212-3 antennas. > > Two of the sites were on 1000+ towers and used a single DB-212 element due > to the large tower face and the great height. One was a repeater using a > receive antenna at 1450' and a transmit antenna at 1350'. The other was a > remote base station with the single loop at about 850'. > > As we were an investigative agency, almost all of the mobiles were using > AM/FM disguise antennas. (Yeah, I know, but we were stuck with the band > that the State Division of Communications had dictated...) Despite the > radiating dummy load antennas, we had excellent mobile coverage in > virtually all of the state. > > A consideration for DB212 antennas is that lining them up on one leg can > make them pretty directional. > > For towers that were very close to the coast, I would put all three > elements on a single leg, but skew them so that only one was pointed > directly off of the leg. This seemed to give me a somewhat cardioid > pattern, but with a little better pattern to the back than if all three > elements were in line. > > Another consideration is that they were designed to be used on Rohn > 45/55/65 sized tower. If you put them all on one leg, a larger tower face > doesn't matter much except that the rearward pattern will likely have a > larger null. Mounting them on all three legs of a larger face tower will > result in reduced gain and a pretty messed up pattern. > > I don't know if I'd worry a whole lot about adding a fourth element- the > three element antenna will deliver excellent results. > > Doug > K4AC > (Running for ARRL Southeastern Division Director- please check out my > website at www.k4ac.com)
