Is it possible the AM signal is getting into an audio stage instead of the receiver front end? I had that happen once.
----- Original Message ----- From: "KT9AC" <kt...@ameritech.net> To: <Repeater-Builder@yahoogroups.com> Sent: Tuesday, February 23, 2010 4:01 PM Subject: Re: [Repeater-Builder] Re: Can the 4th harmonic of 1250 AM keep UHF repeaters locked up? >I was able to match up the audio coming through the repeater and the > local AM station. My latest theory is that their signal is so strong > that its blowing into the receiver's front end and multiplying/mixing > there (past the bandpass filters and all). They are heterodyne receivers > after all. > > I'm considering an ICE broadcast high-pass filter that cuts off at > 1.8Mhz (model 402). I have an email into them to see how well it might > work at 448 Mhz. > > Tony > > tracomm wrote: >> >> Had a similiar situation at our site, a station on 106.7 MHz, music on >> hang time on many repeaters, intermod runs gave no clue to reason, did >> all the usual, grounding, filters no resolve. >> Turned out to be the STL Marti system on 450.100 MHz, from an close >> studio site pointed right at our site, hitting our Rx multicoupler, >> mixing with our transmitters. Resolution was low passs & isolater on >> the STL system. >> Make certain which station the broadcast audio is coming from and give >> the station engineer a friendly call, may reveal some info to help >> your issue. >> >> Chris >> GMRS Inc. >> >> >> --- In Repeater-Builder@ yahoogroups. com >> <mailto:Repeater-Builder%40yahoogroups.com>, Tony KT9AC <kt...@...> >> wrote: >> Hi everyone, >> A while ago I was troubleshooting a bad feedback or "growl" problem >> that was impacting a UHF repeater, of which the short term workaround >> was to not encode TX PL (PL or DPL would keep it locked until the >> signal dropped enough or timed out). >> >> In doing some more research, I found a 1250kHz AM station within a >> mile or two that changes pattern between day and night. The >> interference mentioned above would appear around drive times (like >> 5pm) so that had me chasing other sources. Still, it was puzzling that >> a 5Mhz signal could be causing the feedback (it didn't appear when >> doing normal receiver testing with a service monitor). The recent give >> away was that I could hear talking underneath my test signal (like a >> sports show). >> >> So, if we take the 1250Khz signal or 1.25Mhz x 4 = 5Mhz. I realize >> that the 4th harmonic of a 5KW broadcast station isn't very powerful, >> but being in its nearfield might be enough to cause a mix with the UHF >> transmit output. >> >> Does this make sense? This phenomenon can be duplicated with both a >> 450 and 440 repeater system - both with standard 5Mhz offsets. I don't >> think any sort of filtering would work since the mix happens "in the >> air". >> Only by having split PL's can the lockup be prevented, and equipment >> was both MSF5000 and Micor systems, through correctly tuned duplexers. >> Thanks, >> Tony >> >> > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > > ------------------------------------ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/Repeater-Builder/join (Yahoo! ID required) <*> To change settings via email: repeater-builder-dig...@yahoogroups.com repeater-builder-fullfeatu...@yahoogroups.com <*> To unsubscribe from this group, send an email to: repeater-builder-unsubscr...@yahoogroups.com <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
