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.
In order to make a window filter you need several pass filters in order to make a wide window. Using those filters tuned to a single frequency is much more effective. 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. There are times (rare) that a window filter may be used to pass several transmitters but off hand I can't think of one. 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. 73 Gary K4FMX > -----Original Message----- > From: [email protected] [mailto:Repeater- > [EMAIL PROTECTED] On Behalf Of Richard Sharp, KQ4KX > Sent: Wednesday, January 30, 2008 9:06 PM > To: [email protected] > Subject: [Repeater-Builder] Re: Desense Problem on 222 MHz Repeater > > Yeah, of course you'd want to order any filter optimized for your > application. Yes, DCI markets products for the Amateur market but they > also > have a lot of products for commercial markets. I have indeed used some of > their products (HAM & commercial) and have had very good results. Hi-Q > bandpass cavities is absolutely the best thing for frequency specific > filtering between the TX & RX ports of a duplexer and the transmitter & > receiver but a "window" filer is going to be more appropriate for the > antenna side of the duplexer. DCI is not the only one out there that > makes > window filters either. If you're going to use split antennas a window > filter would not be needed. > > As I think a couple of others have already mentioned a spectrum analyzer > is > a necessary tool in today's RF environment to make sure you're being a > good > "RF neighbor" as well as finding external sources of IMD too. > > Richard > > > "Nate Duehr" wrote: > > Careful. I've looked over their product line and their stock filters > have published SWR numbers that don't look good for high 147 and low 145 > repeaters... they tend to be made for the center of the band for the > end-users, not for repeaters. > > The skirts on even their 4 MHz wide filters start to roll off if your > machines are at either end of the spectrum. > > Check carefully if you choose to use their filters, or call them and ask > them if they'd tune them lower/higher (probably for a charge). > > Better yet, buy big, real, high-Q bandpass cavities and don't mess > around with these little things made for hams at home. > > Nate WY0X > > > > > > > > Yahoo! Groups Links > > >
