Geez, Mike, you're not asking for much, are you? I assume you are using a half-duplex radio for the link, and it receives on 145.110 MHz and transmits to the distant repeater on 144.510 MHz. So, you need a high-Q notch at 146.850 MHz to protect the link receiver at 145.110 MHz, while not affecting the link transmitter at 144.510 MHz. Whew!
It would help if you specified what make and model radios are involved, along with what duplexer and filters are in place. It's not easy to figure out potential fixes without knowing the quality and performance data of the radios. A Micor or Mitrek link radio, with the helical front-end filter, will perform much better than a broadband 2m mobile radio. My first choice would be a bandpass cavity on the TX side of your repeater, to attenuate broadband noise that might fall on the link receive frequency. Since that is not an option, perhaps a coaxial-cable notch filter in the same location might be a solution. Here's one reference: www.repeater-builder.com/ge/datafile-bulletin/df-10002-01.pdf An eight-element beam is major overkill for a link, IMHO, and may be part of the problem. Perhaps a corner reflector would be a good choice. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Mike Besemer (WM4B) Sent: Saturday, September 27, 2008 8:12 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Quarter Wave Stubs/Notching Interference I'm working on collocating a 2-meter remote base with our repeater, and naturally every time the repeater transmits, it makes the remote-base radio totally deaf. I've been playing with quarter-wave stubs with some success (and have lots more ideas/experimenting in mind) but would like to hear from others who are running collocated equipment without the aid of cavities/duplexers. The local repeater is running 30 watts on 146.85 to a DB-224 at about 125 feet. The link is on 145.11 10 watts to an 8-element beam at about 70 feet. The whole purpose of the remote base is to link to another repeater 30 miles away. And before anybody asks, a link on another band isn't a possibility (primarily because of limitations with antenna systems), so it's 2-meter remote base or nothing. Thanks, Mike WM4B
