> Cort Buffington <[EMAIL PROTECTED]> wrote: > Repeater Builders, > I pose to you all a question. I have two UHF duplexers, both 4 > cavity pass-reject. One is a Wacom (the ubiquitous 3U rackmount > guy) and the other is from a Motorola MSR2000.
Both very fine units for what they are. > I have really poor equipment, and don't necessarily "trust" > manufacturer specs. Anybody have an opinion on which one is > better, or pros and cons to each? Nothing bad to say about each one... > The rest of the RF equipment are Hamtronics T304 and R305 > and a Mirage D-1010-RN. The T304 is "throttled" back so > that the Mirage is making about 55-60W. I'm currently running > on the MSR2000 duplexer, not tuned as well as it could be. > Some desense, and some is probably curable with better tuning > of the duplexer, Nat's-a$$ alignment of the duplexer including the notch positions will make a large difference in the overall system performance. > helical preselector on the front end, etc. Depends on how the helical pre-selector is constructed. Some designs have active included active preamplifiers and some are straight forward filters, which are "only so helpful". > But so far, I'm finding the additional receiver sensitivity > (over say a Mitrek/MSR or Micor) is far out-weighing the desense > 73 DE N0MJS > Cort Most of the current Hamtronics Receivers are red-hot in the sensitivity department, pretty fair in the 3rd order intercept performance and "fair" in the "blocking" performance spec. The elephant in the room is the 60 watt output PA and the relatively unprotected receiver front end. A complete/proper duplexer alignment will be the most bang for your buck. In specific you need to ensure the duplexer band-reject notch frequencies are properly spaced. A non-technical broad statement regarding duplexer notch and band-pass operation. Relative to the grand scheme of things more relative performance is often gained with strong/deep notch-out performance (of the unwanted other frequency) versus band-pass only (of the desired frequency). Folks with modest resources often adjust band-pass, band-reject duplexers using the max power into a watt meter/load method. Much system performance is lost when the reject-notch tuning is discounted or ignored for lack of proper test equipment. Unless you know for sure someone has properly aligned the duplexer notch (band-reject) positions you can and should assume they are not exactly in the best possible position. Once again... the duplexer reject notch adjustment is another one of the few repeater performance "free lunch" items, which should not be ignored. Because there are only a few "free lunch" items on the menu. cheers, s.
