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From: alex on 27 Jun 2010 07:32 Il 27/06/2010 4.43, Phil Allison ha scritto: > "alex" >>> >>>>> >>>> thanks phil, >>>> but in the situation described above ... >>> >>> >>> ** Looks to me that you described nothing. >>> >>> >> look better Phil. > > > ** I have. > > You have described nothing in any detail. > > The devil is in the detail ( famous saying). > > > > ... Phil > > > > Santa Maria del fiore (Florence cathedral) http://maps.google.com/maps?client=firefox-a&hl=it&ie=UTF8&ll=43.773193,11.256107&spn=0.001718,0.004292&t=k&z=19 Ok, things happened some 6-7 years ago, in winter, just before christmas, inside the church there are a lot of well known pieces of art, so RMI from a weird security or control system, was the first thing i thougt (under the main floor there is an underground museum, with a lot of electronic protection). So i asked a friend, with much more knowledge than me in radio transmissions, to discover if actually was RMI. His frequency scanner tell us that was nothing affecting the band used for microphones, but we noticed that transmission from a single bodypack lead to a very weak reading on the scanner in opposite to the reading from the same bp outside the church. Moving the scanner around the church the signal stenght varied a little, never reaching the level measured outside, even very close to the transmitter. He told me that, in his opinion, a lot of bouncing with different timing leaded to an heavy cancellation in phase, wich sounded ok for me due the comparision with sound waves. Another brand of system was apparently unaffected by anything and worked well for the show. --- Something very similar happened to me in another church in Florence last year (second job in my life inside a church). Santa Maria del Carmine http://maps.google.com/maps?client=firefox-a&hl=it&ie=UTF8&ll=43.773193,11.256107&spn=0.001718,0.004292&t=k&z=19 They call me because the pa system doesn't worked well, they heard big noises coming from the speakers, like a pickup scratched over a record surface. Due to "art protection authority" new laws, the system was wireless (you cannot use cables) for the audio signals and wired for power supply (pwr outlets where placed all around the church before the law). 3 Transmitters and 6 receivers, from dB technologies, showed the same behaviour: big drops and weak signal even at small distance. After asking the old audio company responsible of the system setup, i discover that they used originally a very powerful radio signal amplifier for the trasmitter with a directional antenna, but had to remove it beacuse people in the near buildings was no more able to watch TV! So they carefully find an antenna position (the regular antenna) to minimize drops, but apprently after 4 years she has moved so i get the call. Even in this second case my suspect go to the cancellation of the carrier due to reflections because the room size (both are very large churches) and the very complex internal geometry. For now my "poor man experience" says: don't use wireless system in churches! bye alex
From: Tim Perry on 27 Jun 2010 13:34 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.
From: Bob Quintal on 27 Jun 2010 19:35 "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.
From: alex on 27 Jun 2010 20:23 Il 27/06/2010 19.34, Tim Perry ha scritto: > 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. thanks a lot Tim, uh, that was a joke, but in churches i know that things may be not so easy. There are churches and churches. I got this problem into VERY big and complex one with the largest and tallest dome in the world. https://secure.wikimedia.org/wikipedia/en/wiki/Florence_Cathedral > > What the problem actually was cannot be determined by discussion or > theorizing. > yes, in the fact the original post was asking if the room shape and size could affect the proper propagation of radio waves at the point to render systems not usable. > 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. agree > > 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. agree with that, i just thougt "statistically" that was at least one system in the bunch to be consider "perfect". I got problems on ALL shure systems (SX 170-180 MHz at the time in italy). In addiction there was some other kind (?) that worked well from the beginning. Just the shures was unusable. In many other location the same systems never gave me a problem. > > 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. > > > ok, all the test i made was conducted with almost empty church, me and another two or tree people, with church closed to tourists. regards alex
From: Tim Perry on 27 Jun 2010 21:55
"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. .. |