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Wireless Power & antenna distribution for 20+ RF mic receivers

Discussion in 'Sound, Music, and Intercom' started by Wolfgang, Aug 24, 2008.

  1. Wolfgang

    Wolfgang Member

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    I run sound for my school's theatre shows. We have a large theatre (1000+ people) and tend to do fairly large shows. As a result, we regularly run 20+ wireless lavs per show. Right now, they are all just stacked (neatly) next to the board, but I am pushing to get them rack mounted this year. I wanted to not have to find place for 20 a/c adapters inside the rack, which lead me to mic distribution systems. The only problem is that they almost always work 1 distributer to 4 mics. That's alot of wasted rack space for the distributers (I think), and the distributers aren't cheap themselves. We have never really had reception problems, so the antenna distribution isn't my #1 priority. Does anyone know of any mic distribution system that will take more than 4 mics or another system that will, per se, have one a/c input and 10 dc outputs?

    As a side note, do the mic's antennas in the back lose alot of reception by being rack mounted?

    Thanks,
    Wolfgang
     
  2. OnWithTheShow

    OnWithTheShow Member

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    re: Power & antenna distribution for 20+ RF mic receivers

    Wolfgang,

    Depending on what size rack you get you can get a power rail for the AC adapters. You might be better off getting a couple paddle antennae and running them to a antennae distro then daisy chaining the receivers it will keep you from having 20 plus opportunities to poke your eye out next time you have to get in the back of the rack.

    What model wireless are you using?
     
  3. soundlight

    soundlight Well-Known Member

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    re: Power & antenna distribution for 20+ RF mic receivers

    While it will definitely void any warranty on the wireless receivers, we had one of the guys who's really, really good with a soldering iron and good with circuits hook up what amounted to a fanout of the proper mini DC plugs to plug in to the wireless, and got a power supply of the proper voltage and more than enough amperage for all of the wireless receivers, and soldered in the connectors so that all of the wireless units in each of our 3 racks are powered from a single power supply, so one power supply per rack. You just have to get the exact voltage power supply, and it's always good to have a little bit of headroom on amperage.
     
  4. jkowtko

    jkowtko Active Member

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    re: Power & antenna distribution for 20+ RF mic receivers

    I just bought the parts to do exactly that -- we have 20 wireless receivers on a rack and they all happen to take 12v 2.1mm DC plugs.

    iofast.com has plugs with 3 feet of cord attached

    advancedgadget.com has plugs with no cord

    cables4pc has 12v 5A power supplies.

    Supposedly 22 gauge wire will handle 5A at 12v, and 18 gauge wire will handle 10A.

    Theoretically all 20 of my receivers (160mA and 200mA) total only 3760mA, so a single 5000mA power supply should work with decent margin of overhead. However I may split between two power supplies and keep a separate Y connector around so I can deal with a broken power supply, if that ever happens.

    I also asked the AKG tech on what voltage specs the wireless receivers require, since the power supply was rated at 12v +- 20%. He said anywhere from 5 to 17 volts would work on these receivers, so it looks like there should be plenty of margin of safety for voltage at least.

    If anyone else knows of issues of doing this or has seen receivers "burn out" please share. The only risk the tech told me was of voltage starvation and receivers losing signal should the power supply be under-powered.
     
  5. Wolfgang

    Wolfgang Member

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    I didn't quite understand what you mean regarding the antenna distros. We use the old sennheiser ones. Almost identical to the current G2's, but the older version.

    Wolfgang
     
  6. DaveySimps

    DaveySimps CBMod CB Mods Premium Member

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    I am unaware of any manafacturer that makes such a product. If you do rack mount you mics as you indicated, there is a great potential to have reduced reception, but it is very difficult to predict since so many other factors are at play. I highly recommend the distrobution units. When wired correctly, they help to create a very reliable wireless system. With the way you describe you setup, you are just running on good luck as far as RF intermodulation and interfearence is concerned.

    ~Dave
     
  7. museav

    museav CBMod CB Mods Departed Member

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    Since I don't think it has been mentioned, but mounting the receivers inside a rack and possibly even in a different location can affect the reception.

    There are pros and cons to a common power supply. It can definitely clean up a rack but if you run everything off one supply then I would suggest keeping a second one handy as any failure will take down all mics. And since most receivers are provided with a power supply, a common supply is usually an added cost rather than any savings.

    I don't know of any standard antenna and power distribution unit for 20+ receivers, however many distribution units will let you cascade multiple units off one set of antennas.
     
  8. OnWithTheShow

    OnWithTheShow Member

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    I took this to mean that you have a small antenna hooked up to each receiver. This leading me to recommend shared paddle antenna.
     
  9. cdub260

    cdub260 CBMod CB Mods

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    For your power distribution I would recommend a rack mount plug strip or three. You can find them from McMaster-Carr. Go to their site and do a search for rack mount plug strips, then when the results page comes up click on Rack Mount. When the next page comes up, click on View Catalogue Page. You'll be presented with a variety of different types. Just look for the one that most closely resembles your needs.

    Hope this helps.
     
  10. Wolfgang

    Wolfgang Member

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    Thanks for all the help. From what I'm hearing, I think I will look into getting distro units for all the mics and then possibly running cascading some of the antennas. THis way, everything is not dependant on one power supply. However, if we can't get all the money to run antenna distros, maybe I will try the homemade power adapters that were suggested above, running perhaps 6 or 8 mics of each adapter so that if one dies, all the mics do go down, as well as keeping a good bag of spare single power adapters about in case part of a power adapter fails.

    That also sounds like it would work quite well, and be quite a bit easier and less time consuming than making the power adapters.

    Thanks,
    Wolfgang
     
  11. Anonymous067

    Anonymous067 BANNED USER

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    Personally, I wouldn't recommend jimmy-rigging the antenna distro and receiver power. You'll regret it when something goes wrong inside and you want to send it back.

    Sometimes (like with Shure's newer distro), it has power connectors ON the distribution unit for the four receivers it gives antenna to.

    If you don't want to buy a TON of antenna distribution systems, you could always not try to go off one pair (AB) antennas, and use four or six antennas.

    If you have 20 systems, you really should have some sort of distribution, as if all the antennas are in close proximity, they might be causing some sort of heard or unheard interference.
     
  12. Chris15

    Chris15 CBMod CB Mods Premium Member

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    I guess a pertinent question that is yet to be asked is what is the rack you are proposing to mount these in made of? A metal rack likely will affect your reception, with a timber rack you might get away with a bit more...

    Could you clarify if you have 20 individual receivers or 10 dual receivers, ie. 10 sets of antennae or 20?

    10 sets of antennae will lead to intermodulation, you seem to have just been lucky in not having it bite you yet. Remember that if you do use antenna distribution, you'd be looking at 3 units I'm guessing, so your first unit has the antennas connected to it and then has a pair of outputs connected to the inputs of each of the other two distros. So you connect 8 receivers to the second two and then 2 receivers to distro number 1.

    As to everyone's talk on power supplies. The 12V 5A supply idea happens to be one that we intend on using to power up a G2 IEM transmit rack. But we'll be making it with 3A supplies as we only need that level of current, but we will be installing 2 3A supplies. When you have switchmode power supplies and you parallel them, you inherently get redundancy. So if one supply dies, the other keeps going... Perhaps this would work for jkowtko in his application...
     
  13. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    I disagree that "10 sets of antennae will lead to intermodulation." Intermodulation is caused when two or more signals pass through a nonlinear circuit element, such as a (poorly designed) amplifier or mixer. The act of having 10 sets of antennas in close proximity will NOT cause this to occur. What is can cause, however, is radiation of the receiver's local oscillator (the signal used to bring the RF down to a manageable frequency) and pattern distortion, from having multiple elements in close proximity.

    That said, in real life, these are almost never a problem. The real reason antenna distribution is used is so that the receivers can share an antenna in a good location, instead of their own antenna in a bad location. It also helps keep the back of the rack clean.

    I would say that if your RF system is working with individual antennas, just keep it that way.

    PS - Wolfgang, are all of your frequencies coordinated properly? I know you said its working, but I ask the question anyway.
     
  14. Hughesie

    Hughesie Well-Known Member

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    if your system is a sennheiser system, they have a fantastic signal distrubution system that limits the amount of antennas you have to have

    [​IMG]
    Helical

    or

    Plate style
    [​IMG]
     
    Last edited: Aug 31, 2008
  15. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    These antennas will work with any UHF wireless mic system, not just Sennheiser units.
     
  16. Wolfgang

    Wolfgang Member

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    We have not bought a rack yet, but it would probably be a fairly large rolling rack, which I believe are generally plastic or wood, obviously with metal reinforcing.

    20 individual receivers. They each have 2 antennas in the back, if that's important.

    Could you explain this further? I don't quite understand what switchmode power supplies are, or how to run parallel power supplies for that matter.

    I believe so, last year we reset all the frequencies so that they are each 5 mhz apart from each other

    Wolfgang
     
  17. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    If they are exactly 5 MHz apart, they're not coordinated properly. :) Essentially, the idea behind coordination is to ensure that combinations of frequencies don't add to other frequencies in your system and cause interference. For instance, if you had a transmitter at 645, 650, and 655 MHz, you would get the following combination: 2*650 - 655 = 645 MHz, which could interfere with the mic at 645 MHz. You can use software like IAS or SIFM to generate a list of frequencies that don't have this problem. See my FAQ for links to these packages. That said, if you've never heard any noise at all (not a single dropout or pop of noise) you probably don't need to have to worry about it.
     
  18. waynehoskins

    waynehoskins Active Member

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    Five megs apart eats up a lot of spectrum inefficiently. Also, especially with the DTV thing, you may have to cram more transmitters in less spectrum: in the Dallas market, there aren't a lot of holes in sub-700-meg UHF TV. I have one 6-meg hole in 600 and possibly two in 500, but even those aren't empty (they have low power stations, and I have decent enough S/N ratio, but it's not an empty channel). They can pack DTV more tightly, and it eats up the full 6-meg channel, so there aren't many places to go once 700 megs goes away.

    By the way, you can do antenna DA on the cheap from your local Radio Shack. A brick preamp and some distribution blocks (and some cables) are all you need. UHF TV bowtie antennas also work fine for wireless microphones. Radio is radio, regardless of whether you care about a television signal or a wireless microphone signal.
     
  19. avare

    avare Active Member

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    +1 on DIY with off the shelf components. A big step up from Radio Shack parts is Mini-Circuits. They also have bias tees, so you can power active antennas.

    Andre
     
  20. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Mostly plastic or wood should not cause you too many problems. Racks like they stick onto walls that are all steel and aluminum on the other hand...

    20 sets of antennae will mean a lot more distribution infrastructure is needed than for 10 dual receivers...

    Mike's already noted the issues with 5MHz spacing...

    Now switchmodes... Switchmodes are the alternative to a linear, big transformer based design. Essentially they do still have a transformer, but it's much much smaller but to be able to do this, you have to run it at a much higher frequency than the standard 50Hz mains frequency, normally in the order of tens or hundreds of kHz.

    But as far as you need to know, that's supremely irrelevant. You take a rack case and mount a pair of supplies like this, except one that is relevant to your voltage and current needs. Chances are someone else sells them at a more reasonable price.

    Yes and no... TV antenna runs on 75 ohm coax and for best results, RF should be running on 50 ohm. And so you will have an impedance mismatch when connecting to a 75 ohm splitter and / or amplifier... There's 6dB gone...

    "Radio is radio". Yes, except that you are talking about transmitters running at kilo and mega watt ratings for TV transmit and milli watts for the RF we deal in... One has a bit more scope for poor practice than the other...
     

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