At 3/7/2009 20:31, you wrote: >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.
...which is why I've never bothered with IMD programs. Put it up; if it works it works. If there's IMD usually the demoded audio in the mix will tell you who's involved in the mix. Even then, knowing what frequencies are involved doesn't help you determine which rusty tower joint is actually producing the mix. The last mix problem I was faced with ended up being a 2A-B, with my output being the 2A & the B a commercial repeater 5 MHz above my output. The mix ended up occurring in the front end of an Icom VHF/UHF multimode radio plugged into an antenna about 30' from the repeater antenna; unplugging the UHF port of the radio eliminated it. Knowing the frequencies involved in the mix played no part in the determination of the source. Bob NO6B
