> [EMAIL PROTECTED] On Behalf Of skipp025 > (window filter cannon fodder) > > > 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.
Let's not shoot ourselves in the foot here. >:) If you need more selectivity for the transmitter or the receiver then put a cavity or two on the appropriate port. You get more for your money that way. If you want DC ground a shorted 1/4 wave stub does wonders. > > > 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. One band pass cavity does not make for a window filter as the term "window filter" is commonly used. Yes a single cavity will pass two or more very close spaced frequencies but it isn't going to pass a tx and rx of a common 2 meter repeater with normal loss. Let's not stretch the term too far. > > > 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... That's true enough. Sometimes several window filters are paralleled to include different segments of the band or a band pass cavity or two are paralleled to accommodate specific frequencies. > > > 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. In transmitter combiner systems individual cavities are usually placed at the output of each transmitter. Sometimes more than one cavity on each transmitter before going to the combine point. That provides the isolation needed between transmitters and the high power present at each and also affords some noise protection to others and to your own receivers. Placing a window filter after that has too many problems. > > > 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. I have seen some guys do some really odd things at sites to make things work but doing it right is usually much more fruitful and less problems. 73 Gary K4FMX > > cheers, > s. > > > > > > > Yahoo! Groups Links > > >
