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]> wrote: > well said > > > > ----- Original Message ----- > *From:* Gary Hoff <[email protected]> > *To:* [email protected] > *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 <[email protected]> > *To:* [email protected] > *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 > Version: 8.0.237 / Virus Database: 270.10.23/1953 - Release Date: 02/14/09 > 18:01:00 > > >
