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U John Callahan M y e Ta Ikiri g SEVERE CASE interference surfaced Houston Texas RC channel 57 Several large expensive models lost number fields Paul King obtained RC Channel Analyzer District VIII frequency representative started looking culprit finding RF interference two Hams Bob McDonald myself heard problem availability AMA Channel Analyzer volunteered assist AMA Channel Analyzer made Aero Spectra hand-held unit size large calculator run nine-volt battery makes completely portable covers band 719-731 Mhz Editors note Newer models cover 50 53 72 75MHz Three displays available first alphanumeric shows frequency MHz channel number signal strength dB second shows full spectrum 72 73 MHz signal frequency range spike up baseband Its vertical axis display calibrated dB 0 dB bottom 60 dB top screen third called zoom channel selected centered screen can see 30 kc side selected frequency channel primary display used Analyzers available District Frequency Coordinator further information availability first coordinated attempt construct two-element Yagi beam use signal strength alphanumeric display strobe interference resulted number bearings did intersect unusable appears reflections fact signal shifting frequency 120-cycle rate prevented locating general area interference located Yagi beam Buildings towers gave reflections stronger basic signal observed zoom display interfering signal seemed start around 7294 MHz pager frequency sweep down 7293 MHz RC channel 57 local office FCC visited list licensed users 7294 MHz obtained checked telephone book listed company company visited advised given frequency up last July used California FCC Gettysburg PA contacted names two current users frequency 7294 Mhz Houston obtained along latitude longitude transmitters analyzer driven sites neither culprit Bob McDonald took analyzer found signal appeared strongest Its easy finally find source south town corresponded area hardest-hit RC fields located used analyzer Ham directionfinding techniques find what appeared hot spot near Houston FM towers obtained frequencies tower adjacent TV tower input Intermod computer program two hits identified frequencies involved hits channel 57 type would generate interference existed Channel 57 An all-band scanner also tuned interference output displayed scope audio signal sounded like raw AC scope showed signal appeared repetitive corrupted sawtooth pattern took data another Ham chief engineer local FM station After looking hearing interfering signal said bad power supply part pager system due its location radio spectrum An outside-car Ham antenna connected analyzer started driving toward couple 500-foot towers south Houston pager systems installed As first tower approached signal strength zoom display continued increase until 50 dB signal strength base tower Bingo Its easy finally find source engineer access buildings base tower found five large cabinets building analyzer did show increase signal strength however placed next cabinet engineer momentarily pulled power cord cabinet third cabinets cord pulled interfering signal disappeared analyzer power restored signal reappeared 7292 MHz no longer impinged channel 57 malfunctioning transmitter output 100 watts antenna 500 feet interfering signal covered wide area unit used phase transmitters large paging system company switched satellite system system being kept backup Since satellite system failed malfunction backup detected until found team Some suggestions have interference trying locate source analyzer loaned AMA very useful observing interfering signals hest way locate interference seems observing signal strength Select intersecting roads interference can seen analyzer Determine location along both signal disappears Draw ellipse through four points map Search near center towers antennae signal might originate use analyzer pinpoint location signal strength Secure help professionals identify commercial broadcast signals Show data signal analyzer get interference corrected will have contact tower owner get tenants tower contact individually suggest soft approach operators can catch flies honey vinegar old Irish granddad used say John Callahan 430 E Gaywood Houston IX 77079 9May1996 67 time time section will present thought-provoking ideas modeling/AMA issues Timeliness available space factors may affect pubi ication opinions expressed authors shouldna construed being AMA Headquarters staff ortheAMA officers