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Matthew Steel

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    Live sound and recording for higher education
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  1. This is a totally different direction, but would a good podium mic meet your needs? I could not recommend the sound of the Shure or AKG podium mics I have worked with, but I have some experience with the Countryman Isomax 4rf and it sounds reasonable, especially for the price.
  2. I think you will still need something like diodes to isolate the two batteries, but using one battery at a time should be a workable strategy. The diodes will drop about 0.6v which will equate to some small amount of lost power. Even with two different types of batteries, as long as they are the same nominal voltage things should still work. Run off the first battery until is nearly discharged, then add a fresh battery to the empty slot. At that point the fresh battery will take over the entire load because its voltage will be higher (and the diode will prevent it from charging the spent battery). Then you can remove the spent battery for recharging.
  3. If the IFB just needs to be listenable and not pristine, then you may even be able to keep the transmitters in digital hybrid mode. Come to think of it, you'd probably need to disable pilot tone on the receiver for this to work. We use our transmitters in NA and NU digital hybrid modes and we also use a Uniden scanner to monitor them. The scanner is a consumer model marketed toward motorsports fans, and I'm pretty sure it is just doing straight FM demodulation. I think the the digital hybrid signal includes as an FM component that is a prediction error. So, the scanner is not picking up "the" signal, but it contains enough information to hear the mic and to detect many types of problems.
  4. Thanks, @PMC Since my location doesn't change I only scan periodically to look for changes in the environment. I use Shure Wireless Workbench for coordination since it supports lots of different manufacturers out of the box. I don't think I could get by without WWB's zone features. I can define zones for different buildings, etc. I try to make it so our portable systems and media groups can power their stuff on any time, anywhere on campus and "just work" without changing anything, but that small systems far away from each other can even use duplicate frequencies if need be. Things have been quite reliable. That's why I want to make sure any additional telecom equipment doesn't ruin my life
  5. Thanks for your comments, Larry. I think you would approve of the multicouplers I have in place. I haven't spec'd all of them on campus, though....
  6. Does anyone here have insight into operating wireless systems in close proximity to high power transmitters? Or any fanatical RF gurus willing to chime in about the potential risks? I am a staff audio engineer at a university, and I have become the de-facto RF coordinator. I keep track of over 100 UHF wireless systems spread across our 225 acre campus. I have been asked about the impact of potential telecommunication equipment installation (e.g. cellular antennas) on buildings. The information I have does not specify frequencies or technologies, so I have to assume "telecommunications equipment" could include traditional cellular 1GHz and up, 600-700MHz band cellular, and even TV whitespace devices (or even other technologies of which I am not yet aware). My first inclinations are: * Cellular > 1GHz would generally not be a problem since it pretty far away from UHF (and we don't operate any 941 band devices). * Cellular in the 600MHz and 700MHz bands might require us to be more careful about filtering on our antennas, particularly where we have wideband multicouplers in use. * TVBD or white space devices would be a big problem since they would be right on top of us. The part I am not as well versed in, is intermodulation inside the transmitters themselves where a high powered transmitter might be within a couple hundred feet of a location. A quick estimate with the inverse square law leads me to believe that if a 50mW transmitter could generate problematic intermodulation in another transmitter at 3ft, then a (typical?) 100W transmitter would be a similar problem at 136ft. Real world issues like directional antennas, intervening structures, etc. could help with that but that seems like it actually could be a potential issue. Thanks for reading and for any insights you're willing to share.
  7. The problems I have heard about with occupancy sensors don't involve RF. Rather some use ultrasonic signals as the detection mechanism. These signals, though inaudible, can be quite strong and can be picked up by a microphone. In certain transmitters, the low pass filtering on the input is not sufficient to prevent the ultrasonic signal from having an effect on the compander stage. This creates artifacts that show up in the audible frequencies.
  8. I don't think that would work. The Betso runs on a single AA battery (1.5v) and the Lectrosonics L series would run on 3.0v with their two batteries in series. The Lectrosonics SM form factor transmitters, on the other hand, do run on 1.5v, with the two-battery versions having the batteries in parallel rather than in series. So maybe the corresponding BattElim would work.
  9. I didn't see a battery eliminator for the LMb listed on the Lectrosonics site either. I realize for you the time zone difference is significant but you might try calling Lectrosonics to see if the battery eliminator for the LT or LR could be made to work. It appears like they would be electrically compatible but it also appears the screw holes don't match up. Besides the curved vs square battery door shape.
  10. Have you tried changing frequencies to see if it makes any difference? And of course, have you run an intermodulation calculation on your frequencies?
  11. I have used some Lectrosonics 185 systems regularly over the years, not so much recently. They generally did the job but had some drawbacks. Some of the drawbacks are inherent in the frequency band, others would depend on the specific equipment. Another limitation was related to FCC regulations of the time that have recently been amended to improve things. Inherent in the band: 1) Low frequency means large antennas. For receive antennas we had large Yagi antennas installed in one location and used coax whips other places. The Yagis were reliable, the whips less so. On the transmitter side, however, the microphone cable shield was the RF antenna, and so care had to be taken that the cable stayed relatively long and straight for best performance. This is probably a reason much of the VHF use today is IFB or similar. Specific equipment: 2) Most systems were fixed frequency. Not as flexible for avoiding other users, but on the upside, it did allow the RF design to incorporate tighter filtering which was good for performance. 3) No diversity. I'm not sure how big a problem this really was, but it did seem that we'd have places with nulls and I expect diversity would have helped. Regulation: 4) VHF systems were (and still are to some degree, I believe) limited to a handful of specific channels. Originally, the allowed frequencies had been chosen without much (any?) regard to intermodulation in multichannel systems. Regulation changes that took effect with the 600MHz auction introduced a new coordinated frequency set that is better for operating more systems simultaneously.
  12. I have a DCR15/1A6U (supply for Venue 1) here on my desk. The plug on that looks like what you describe: Barrel outside diameter of 5.5mm and center pin socket diameter of 2.1mm. I too would be glad to hear an official spec or even a recommended part number. I was trying to find a compatible panel mount - making something I'd like to be compatible with the extra Lectrosonics wall warts I have lying around.
  13. @jawharp, the IR sync format is not the same as the audio dweedle tones. However, it is a fairly simple protocol that uses a standard 38kHz IR frequency and modulates it with 300 baud asynchronous serial data. Unidirectional only. Yes, Raspberry Pi GPIO has enough current drive capability to supply an IR LED.
  14. You may want to check out rabbitears.info. It is geared toward TV reception, but it has a lot of information that is useful for wireless microphones. The "Signal Search" tool in particular is very similar to the way I remember the old Sennheiser tool.
  15. It's been a few weeks, so maybe airing them or other things you have tried have been sufficient. I just wanted to mention that I bought a house where the previous owners smoked. The real estate agent provided us with an ozone machine. We closed up the house and left it unoccupied for a weekend with the ozone at its highest setting. It seemed to help. I won't speculate on what ozone would do for microphones, though.
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