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From: Denny Strauser on 28 Jun 2010 01:31 Bob Quintal wrote: > These Florentine churches, unlike most in America, have large domes > sheathed with copper. Stone walls would not trigger reflections in > sufficient strength to cause problems, but a dome, shaped like a > reflector might be a possibility. Are you saying that that Phil Allison's claim that ALL surfaces reflect RF? - Denny
From: bob u on 28 Jun 2010 01:47 On 6/27/2010 6:35 PM, Bob Quintal wrote: > "Tim Perry"<timperry(a)donespameroadrunner.com> wrote in > news:i0823j$ubm$1(a)news.eternal-september.org: > >> For now my "poor man experience" says: don't use wireless system >> in >>> churches! >>> >>> bye >>> alex >> >> Alex, the thousands and thousands of churches that employ wireless >> daily would disagree with you. >> >> What the problem actually was cannot be determined by discussion >> or theorizing. >> >> Each transmitter and receiver must be tested fully buy competent >> technicians that are fully equipped with radiation test fixtures >> and/or field strength meters plus accurate frequency and >> modulation measuring test equipment. >> >> If (and that's a big IF) it is determined that the equipment is in >> no way faulty, than you can start investigating strange RF >> properties like milti-path. >> >> One problem with tracing local interference problems in a church >> is it is usually attempted when the church is almost empty. When >> it fill with people who bring in there portable electronic >> devices, plus security, maintenance , and anyone else with >> transceivers, the RF spectrum tends to get pretty crowded. >> > Alex and Tim, > > I've worked designing building and testing antennas for over thirty > years, and alex's description of the churches triggered a thought. > > These Florentine churches, unlike most in America, have large domes > sheathed with copper. Stone walls would not trigger reflections in > sufficient strength to cause problems, but a dome, shaped like a > reflector might be a possibility. There is one old brick and stone local church here with a large dome over the seating area. it acts like a large parabola and reflects sound straight down like a laser. a few seats in the church have an interesting sound perspective.... bob
From: bob u on 28 Jun 2010 01:50 On 6/27/2010 8:55 PM, Tim Perry wrote: > "Bob Quintal"<rquintal(a)sPAmpatico.ca> wrote in message > news:Xns9DA4C75AADBC4BQuintal(a)69.16.185.250... >> "Tim Perry"<timperry(a)donespameroadrunner.com> wrote in >> news:i0823j$ubm$1(a)news.eternal-september.org: >> >>> For now my "poor man experience" says: don't use wireless system >>> in >>>> churches! >>>> >>>> bye >>>> alex >>> >>> Alex, the thousands and thousands of churches that employ wireless >>> daily would disagree with you. >>> >>> What the problem actually was cannot be determined by discussion >>> or theorizing. >>> >>> Each transmitter and receiver must be tested fully buy competent >>> technicians that are fully equipped with radiation test fixtures >>> and/or field strength meters plus accurate frequency and >>> modulation measuring test equipment. >>> >>> If (and that's a big IF) it is determined that the equipment is in >>> no way faulty, than you can start investigating strange RF >>> properties like milti-path. >>> >>> One problem with tracing local interference problems in a church >>> is it is usually attempted when the church is almost empty. When >>> it fill with people who bring in there portable electronic >>> devices, plus security, maintenance , and anyone else with >>> transceivers, the RF spectrum tends to get pretty crowded. >>> >> Alex and Tim, >> >> I've worked designing building and testing antennas for over thirty >> years, and alex's description of the churches triggered a thought. >> >> These Florentine churches, unlike most in America, have large domes >> sheathed with copper. Stone walls would not trigger reflections in >> sufficient strength to cause problems, but a dome, shaped like a >> reflector might be a possibility. > > hummm... now Alex mentioned it is VHF freqs. It's about the 1.7 meter band. > There is no question that RF does bounce. This can easily demonstrated with > a ham radio, a direction antenna, and a water tower. > > here is a recap of the described problem: >> I had some 20 shure wireless systems, all very close in frequency and all >> in > perfect working order. All showed the same behavior: in a particular > spot in the cathedral (close to the main entrance) we had a lot of > drops. Unluckily that was the "stage" area > > I recently had occasion to contact shure about the ULX product. The > applications engineer told me that operating the transmitters within 15 feet > or (5 meters) may make the receivers overload. > > While a large copper dome may make a decent Faraday shield, I doubt that as > a resonant cavity that it would be tuned to any frequency that would be of > interest to this situation. as a reflector, if it has a focal point at all > it would most likely not be near the entrance. > > If the same system of 20 VHF transmitters works fine elsewhere, I would > guess at local interference. > > > . > > I have had good luck with the ULX series. as long as the frequencies are clear and the paddles are up. I have sweated out a pack before, but that comes more under abuse. bob bob
From: geoff on 28 Jun 2010 02:20 alex wrote: > Another brand of system was apparently unaffected by anything and > worked well for the show. Not necessarily anything to do with the 'brand'. The physics of reflections and cancellations are very FREQUENCY dependant. Reflections and cancellations have nothing to do with interference - a totally different matter. Another aspect is interference resulting from intermodulation products, especially when multiple transnmitters operating in close proximity. Frequency plans can be developed especially to avoid intermodulation upsetting things. Mixing different brands complicates that immensely. geoff
From: alex on 28 Jun 2010 07:45
Il 28/06/2010 8.20, geoff ha scritto: > alex wrote: > >> Another brand of system was apparently unaffected by anything and >> worked well for the show. > > Not necessarily anything to do with the 'brand'. The physics of reflections > and cancellations are very FREQUENCY dependant. > > Reflections and cancellations have nothing to do with interference - a > totally different matter. > > Another aspect is interference resulting from intermodulation products, > especially when multiple transnmitters operating in close proximity. > Frequency plans can be developed especially to avoid intermodulation > upsetting things. Mixing different brands complicates that immensely. > > > geoff > > agree geoff, i said "brand" to refer to a complete different system on different freq range. Unfortunately i don't remember exactly what system i used in conjunction with shure and the freq range. I needed to rent another bunch of different system because we had only 8 and, if i remember correctly, the shures SC had only 8 or 10 possible freq setting so you can had no more than 8-10 system together. Shure SC was the type of system i used almost everytime so i can remember type and model, not the same for the other but maybe it was something from dB Technology. I tell you dB because i know that company own today a lot of dB but i don't remember. As soon i discovered the first malfunction i obviously started a troubleshooting process to isolate the problem so i tested surely one system at once leaving other off, moving antennas back and forth, changing the individual freq for TX and RX. So i can tell you now that EVERY SINGLE shure SC in the VHF band, tuned on every available "channel" refused to work in that church, even alone. All other systems "unknown" worked without problems. As i told we do a freq scan in the affected range but we discovered nothing at all that could cause interference. just outside the door systems started to work perfectly again. carrier cancellation was the only "obvious" explanation i found, but i can't go further. i have no extra knowledge on radio transmission right now. thanks alex |