> > 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.
Sometimes a cavity or two won't easily/properly fit the task/techical requirement. > If you want DC ground a shorted 1/4 wave stub does wonders. Why add another possible impedance bump when the proper choice of cavities or equipment can provide or does the same function. ... if you need that function (a dc return). > One band pass cavity does not make for a window filter as > the term "window filter" is commonly used. ... by a group of people who normally work with both types... > 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. I can easily get a single cavity to pass a 600KHz two-meter repeater with the expected normal loss. Not something I often need to do but there is no real stretch required.. > 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. Then you clearly haven't worked with every possible combination of transmit combiner. > 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. An Amen from the crowd. Keep in mind the right thing can also be odd thing. It takes one cluster $#%& busy mountain top to make one a believer. cheers, s.
