Joe, The transmit frequencies are separated by 600 kHz, not 1.2 MHz (147.360 - 146.760 = 600 kHz), which causes mixing products to fall exactly on the inputs.
73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of MCH Sent: Sunday, February 15, 2009 11:19 AM To: [email protected] 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 <[email protected] <mailto:glaenzer%40verizon.net> > <mailto:[email protected] <mailto:glaenzer%40verizon.net> >> wrote: > > well said > > > > ----- Original Message ----- > *From:* Gary Hoff <mailto:[email protected] <mailto:k7ney123%40q.com> > > *To:* [email protected] <mailto:Repeater-Builder%40yahoogroups.com> > <mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.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:[email protected] <mailto:wa5luy%40cablelynx.com> > > *To:* [email protected] <mailto:Repeater-Builder%40yahoogroups.com> > <mailto:[email protected] <mailto:Repeater-Builder%40yahoogroups.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 <http://www.avg.com> > > Version: 8.0.237 / Virus Database: 270.10.23/1953 - Release > Date: 02/14/09 18:01:00 > > > > >
