Milt; Not to make light of your observation "just the program spitting out all the combinations that COULD cause a problem"
But..........this discussion brought to mind a statement made by a Motorola engineer at a school about multicouplers, splitters, combiners, etc back in 1984; they were discussing the multitude of repeaters on the John Hancock building (or maybe it was Sears Tower) in Chicago "One 'wrong' frequency allowed onto a site can 'poison' the site for everyone" I guess that means run the IM program BEFORE any new TX is added...not after problems crop up............ Gary ----- Original Message ----- From: Milt To: Repeater-Builder@yahoogroups.com Sent: Saturday, March 07, 2009 10:31 PM Subject: Re: [Repeater-Builder] Understanding Intermod Kevin, I recall a case where several UHF community repeaters were installed at a single site. This was not a pretty picture since there was no way to achive vertical seperation and transmitter combiners/receiver multicouplers were not as popular as they are today. An intermod study weas run on the site and at either the 5th or 7th order, every receiver on the site should have been experiencing intermod from a combination of all the transmitters. Of course this was not the case. It was just the program spitting out all the possible combinations that "COULD" cause a problem. All intermod programs just do the mathmatical combinations and report the outcomes, even outragous ones that are not likely to naturally occur. Some do a better job than others of taking into account things like receiver bandwidth and other factors. Actually finding the source where the mix is taking place much more difficult. The benefit of such programs is that they can easily do the math for you, but you have to decide which numbers are good possibilities and which ones are red herrings. Milt N3LTQ ----- Original Message ----- From: "Kevin King" <kc6...@comcast.net> To: <Repeater-Builder@yahoogroups.com> Sent: Saturday, March 07, 2009 8:59 PM Subject: RE: [Repeater-Builder] Understanding Intermod > Bob Ok so much for the software. > > One other user today mentioned a possible issue with another repeater. > 147.300. All I had been looking at with the software were the transmitters > at his site. > > Ok so I plug that into the mix of xmiters in the software and bingo. > > A+B-C 146.70 + 146.70 - 147.30 = 146.100. > > The repeater 146.70 does have a circulator. > > Again this intermod is not my best area. I had the repeater owner keep the > 146.700 xmitter up them had him hit the 147.30 with an HT and yep we got a > burp of noise. But he heard at least 3 repeaters come up. > > So if this mix is the one that is causing all the issues, now we just need > to find where the mix is occurring. Any ideas on where to look? > > As you can see in the full printout from the intermod tool. There are more > that one set of possible offenders. > > -----Original Message----- > From: Repeater-Builder@yahoogroups.com > [mailto:repeater-buil...@yahoogroups.com] On Behalf Of n...@no6b.com > Sent: Saturday, March 07, 2009 3:47 PM > To: Repeater-Builder@yahoogroups.com > Subject: Re: [Repeater-Builder] Understanding Intermod > > At 3/7/2009 08:59, you wrote: > >>I did a analysis on a transmitter site using the TCS intermod tool to see >>what mixes could be causing some issues at this site. I ran the 1-3 order >>and 1 to 5 order. >> >> >> >>So I do not use these tools much and was wondering if any of my fellow >>engineers on here have used this tool and have comments on the output. For >>example this line from the output confuses me: >> >>A+B+C-D-E: 146.70000 + 145.77000 + 145.09000 - 145.73000 - 145.73000 = > 146.10 >> >>It is a hit right on the input but how do you minus 145.73 twice? Is this >>just an issue with the program I am using? > > I should say 146.700 + 145.770 + 145.090 - 2 * 145.730 = 146.100 > > It's actually an A+B+C-2D mix. > > Bob NO6B > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > ------------------------------------------------------------------------------ Checked by AVG - www.avg.com Version: 8.0.237 / Virus Database: 270.11.9/1989 - Release Date: 03/07/09 18:43:00
