> I can't imagine why you would want to put a "window filter" > between your duplexer and antenna line. There is much more > to be gained by putting separate band pass filters on the > tx and rx ports.
There can be good reasons for including a window filter with a duplexer. Reduction of high powered signals, which are IF Images would be one such appplication. Sometimes a plain jane duplexer just isn't enough. Sometimes a duplexer doesn't provide a DC return to ground, which is nice to have when/where possible. > In order to make a window filter you need several pass > filters in order to make a wide window. Any number of band-pass cavities can be a window filter.... even one. Actually a lot of different cavity types can be window filters. BpBr Cavities can and have been used as tx and rx window filters. > Using those filters tuned to a single frequency is much > more effective. I wouldn't put that in stone... It actually depends on the need and the application. > A window filter is effective and commonly used if you > have several receive frequencies that you are pulling off > of one antenna and going to a multicoupler. One of the more commmon applications when the receive window band schemes work out... ie the UHF band most often when everything in the world is perfect... In most busy areas you'll rarely find the perfect world in any commercial and amateur band. Someone is always up to something funky... > There are times (rare) that a window filter may be used to > pass several transmitters but off hand I can't think of one. ... in Antenna Combiner Systems where you must avoid mixing with other signals in the adjacent band(s). Also some other creative applications. > There used to be a company or two that made VHF crystal > filters that were used ahead of receivers to cure stubborn > problems. > They were quite expensive. I don't know if anyone still > makes them. Piezo Technologies in Floriday, now using a new name of MTRONPTI http://www.mtronpti.com/ Yeah, they're expensive but they work fairly well for very pesky problems in the VHF Band, which are very hard to deal with with bottles (cavities) and wider pre-selectors ... with the corresponding insertion loss. Every filter and combiner part has multiple applications. You don't learn about some of the other options until the gremlins arrive. cheers, s.
