Has nothing to do with the spacing, but with the intermod products generated by the two transmitters exactly 600 kHz apart generating spurious signals on the inputs of the receivers. Gary - K7NEY ----- Original Message ----- From: MCH To: Repeater-Builder@yahoogroups.com Sent: Sunday, February 15, 2009 12:19 PM Subject: Re: [Repeater-Builder] Re: Help with intermod between repeaters.
18 miles apart and 1.2 MHz separation? How far apart do you want to space repeaters? I know of repeaters only 210 kHz apart at the same site that work fine. Joe M. AJ wrote: > When were these two repeaters coordinated? RX freq so close to the TX > freq of the other repeater doesn't exactly sound like a good engineering > practices, even with 18 miles between the two sites... > > On Sun, Feb 15, 2009 at 9:37 AM, Gary Glaenzer <glaen...@verizon.net > <mailto:glaen...@verizon.net>> wrote: > > well said > > > > ----- Original Message ----- > *From:* Gary Hoff <mailto:k7ney...@q.com> > *To:* Repeater-Builder@yahoogroups.com > <mailto:Repeater-Builder@yahoogroups.com> > *Sent:* Sunday, February 15, 2009 10:33 AM > *Subject:* Re: [Repeater-Builder] Re: Help with intermod between > repeaters. > > */This is one of the toughest intermod products to solve. 2 > transmitters/* > */600 kHz apart generate spurs every 600 kHz on both sides of each/* > */transmitter. When we were co-ordinating repeaters, it's one > parameter/* > */we always looked at, and tried to keep nearby repeaters off of > that/* > */600 KHZ separation boundary. Are Both repeaters having > problems or just yours?/* > */These signals don't even have to be generated in your equipment,/* > */I've seen them generated by stuff externally and if you look > at a /* > */spectrum analyzer when both transmitters are on the air, > you'll see/* > */the Christmas tree like display showing the spikes every 600 > kHz decreasing/* > */with amplitude as they get farther away. Most suggestions > made may/* > */help and all I can say is good luck, the only real way out of > this/* > */problem may be a frequency change for one or the other machine.]/* > */Gary - K7NEY/* > > ----- Original Message ----- > *From:* wa5luy <mailto:wa5...@cablelynx.com> > *To:* Repeater-Builder@yahoogroups.com > <mailto:Repeater-Builder@yahoogroups.com> > *Sent:* Sunday, February 15, 2009 6:15 AM > *Subject:* [Repeater-Builder] Re: Help with intermod between > repeaters. > > Thanks to all for your replies. > > Joe M wrote > "You need to reject the opposite TX on each repeater. Your BP > filters were set wrong. You rejected the RX on the TX side - > something the duplexer should be doing already. You need to > install > them in the repeater and reject the other TX. IOW, install a > filter > in the .16 repeater and notch the .36 TX. A good duplexer > should do > this as well, but many don't." > > Joe that's what I thought I did. Maybe I did not make myself > clear. I > put a BPBR cavity rejecting 146.76 and passing 147.36 > between the > repeater transmitter and the duplexer at the 147.36 > repeater. This > is where I was surprised that the mixing got worse. If I put > the > cavity in the wrong place let me know. > > Eric Lemmon WB6FLY wrote > "The first question that enters my mind is, were both Micor > stations > originally built as repeaters, with the extra filters and > shielding > plates,or are one or both base stations that have been > converted to > repeaters?" > > I built our repeater. It's the 146.76 machine. It was > originally a > pager TX. All shielding and the lo pass TX filter is in > place. I have > looked at it with a spectrum analyzer and see no other > signal than > 146.76. I have no idea as to what the other repeater was > made from. I > will take a second look at their TX. The next time I go down > there I > plan to take a 50 watt radio and connect it to their > duplexer to try > to eliminate or prove their PA has a problem. > > "The second question is, > are either or both repeaters equipped with ferrite isolators?" > > The 146.76 has no isolator. The 147.36 has a brand new, I > believe > Sinclair, isolator that was factory built for this > frequency. The > isolator has no affect on the problem although I don't think > it's > installed properly. I did not notice when I was there but I > think > it's mounted on a steel plate. Also there in no cavity > between it and > the duplexer. The mixing is there with or without the > isolator in > line. They paid big bucks thinking this would fix the > problem. By > the way they also replaced their antenna and feed line which > may have > made the mixing worse. > > John wrote > "I hate to tell you, a definite way to eliminate > the problem, is a frequency change so that the > output of the two transmitters are no longer not 600 khz apart." > > Funny that`s the first thing I told them. I am familiar with > two > pagers 600 khz apart and the havoc that can be raised. > > I plan to go back down there when I have time and let the > group know > what I find. > Again thanks to all. > > ---------------------------------------------------------- > > > > Checked by AVG - www.avg.com <http://www.avg.com> > Version: 8.0.237 / Virus Database: 270.10.23/1953 - Release > Date: 02/14/09 18:01:00 > > > > >
