Mike, You mentioned that you can't climb the water tower, so I guess trying to move the antenna into a null or putting some sort of shield is out. With the repeater 30 miles away, can you use a push up pole with the yagi on it? The water tower itself may act as a shield if it is placed in the right place. You might could get away with a pretty short pole if a yagi is used.
73, Robert --- In Repeater-Builder@yahoogroups.com, "Mike Besemer \(WM4B\)" <[EMAIL PROTECTED]> wrote: > > Eric, > > > > Yeah. we're always trying to do something for nothing! We're a low-budget > operation and I'm pretty much left to my own devices to try things that the > club wants to do. The good thing is, if this one just doesn't come to > fruition, we haven't spend any money on it. > > > > The radio is an old Yaesu Memorizer. I'm sure that the front end (or lack > thereof) is a major part of the problem. > > > > I've looked at the site noise on a spectrum analyzer and the repeater seems > clean at the link frequency (with the spectrum analyzer hooked to the link > antenna) so it's just poor rejection on the part of the Yaesu. With the > antenna unhooked, there is no noise (additional . beyond normal static) on > the Yaesu with the repeater transmitter on and with the Yaesu hooked to a > signal generator, the repeater transmitter has no effect. so the offending > signal must be coming through the antenna. > > > > The beam is (unfortunately) also a given. We can't climb the watertower but > we're allowed to use an antenna already in place. so we're stuck with what > we've got. > > > > I've been looking at that GE bulletin already. that's actually my next plan > of attack. A plain quarter-wave stub has actually been fairly effective > (much to my surprise) but I need to do better. > > > > I'll keep plugging away at it. it may turn out to be a total bust or perhaps > a case of 'okay. this is as good as it gets'. > > > > I knew I was out of my mind when I volunteered to become the repeater > manager! > > > > 73, > > > > Mike > > WM4B > > > > From: Repeater-Builder@yahoogroups.com > [mailto:[EMAIL PROTECTED] On Behalf Of Eric Lemmon > Sent: Saturday, September 27, 2008 11:57 AM > To: Repeater-Builder@yahoogroups.com > Subject: RE: [Repeater-Builder] Quarter Wave Stubs/Notching Interference > > > > 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:Repeater-Builder%40yahoogroups.com> > [mailto:Repeater-Builder@yahoogroups.com > <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Mike Besemer > (WM4B) > Sent: Saturday, September 27, 2008 8:12 AM > To: Repeater-Builder@yahoogroups.com > <mailto:Repeater-Builder%40yahoogroups.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 >
