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Shure ULX Antenna

Discussion in 'Sound, Music, and Intercom' started by Grog12, Apr 23, 2008.

  1. Grog12

    Grog12 CBMod CB Mods Premium Member

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    Recently my wife (a costumer) asked me if I knew of any reason that a ULX body pack's atenna couldn't touch the skin of a performer. Apparently the SD/Engineer she has been working with was throwing fits about this happening.

    Now I know we all use some form of sheath (whether a condom or something else) to protect the packs themselves, buy typicially I've seen the atenna sticking out.

    Anyone got a good answer to this? The UG doesn't make mention of it at all.
     
  2. avkid

    avkid Not a New User Fight Leukemia

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    Don't let it touch metal or coil it.
    -
    Not touching skin seems ridiculous, especially since I've been doing it for 5 years.
     
  3. Grog12

    Grog12 CBMod CB Mods Premium Member

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    Funny...that was my first reaction...almost word for word.
     
  4. mbenonis

    mbenonis Wireless Guy Administrator

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    The reality of bodypack transmitters is that there is simply no ideal way to use them (OK, if you put them on a wooden stick in the middle of a field, 20 feet in the air, you'll get close to ideal). The body itself does all sorts of crazy things to the antenna's impedance, and there's nothing you can do about it. I would say that it shouldn't matter if the antenna is touching the skin, unless the insulation is gone and the antenna is making direct (ohmic) contact with the skin - in that case, just put electrical tape over it and call it a day. As far as metal goes, I would try to keep the antenna away as a general rule - it'll cause much more problems than the body will. Don't worry about coiling the antenna - it really doesn't make that big of a difference.

    If you're having reception issues, the first thing I would do is move the receivers closer to the stage, and make sure you're not using massive amount of splitting without amplifying the signal. Also make sure your frequencies are coordinated properly and that there are no very strong signals in your bandsplit (i.e., a TV station) which might be desensitizing the receivers. These things will cause MUCH more in the way of problems than a coiled TX antenna.
     
    Last edited: Apr 23, 2008
  5. DaveySimps

    DaveySimps CBMod CB Mods Premium Member

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    Although technically speaking, this could effect the overall response of the unit, I agree with the previous two posts, that it is not a real issue. I took a class with Gino Sigismoundi from Shure about RF issues and their mic systems. He did clearly state that an over all problem with RF systems in theatre is that you are, essentially, broadcasting through saltwater (the human body) before the signal gets to the receiver. He did say that, assuming the RF system is set up correctly (antennas in the right direction, use of distrobution systems, etc.) that any of their mic systems should not have any issues with this. It soulds like the Sound Designer in this instance is overly concerned with somehting so minute that it is ridiculous.

    ~Dave
     
  6. avare

    avare Active Member

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    I have had transmission failures when the antenna touched moist (sweaty) skin. It can cause a problem. It is not as dramatic (pun intended) or against code, but would you not repair broken ground pins on electrical plugs you have because no one has ever had been electrocuted while working with you yet?:p

    Andre
     
  7. Grog12

    Grog12 CBMod CB Mods Premium Member

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    avare? Was it a recreatable problem?

    Here's why I ask......I've been asking this question around ALOT lately and you're the first person with the issue.
     
  8. mbenonis

    mbenonis Wireless Guy Administrator

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    avare, did the radiating element actually touch the person? I.e., the metal part of the antenna and not just the rubber coating on the wire? I would suspect that it was actually a metal-on-skin contact to cause a transmitter failure...
     
  9. avare

    avare Active Member

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    The outside plastic/rubber cover on the antenna.

    No, I did not try to recreate the problem. I solved it immediately. Think about it. The wet body acts like a huge capacitor plate.

    If you are certain that you performers do not sweat, then don't worry about it.

    Paraphrasing slightly, an amateur sets up so it can work right. a professional tries to set up the system so it can't go wrong, wherever predictable.

    Andre
     
  10. Grog12

    Grog12 CBMod CB Mods Premium Member

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    While I'm mildly insulted that you insinuate I'm not a proffesional...I have a feeling that's not your intent.

    Yes the human body acts as a large capacitor plate. But its going to do that whether or not the anntenna touches the skin.

    Part of troubleshooting is knowing exactly what a problem is and not just assuming. Hence my question of was the problem recreatable. If you pull the atenna off the skin and it works touch it to the skin and it fails again there are about 5 other things that could be the problem; Loose attena connection being the first that pops to mind.
     
  11. mbenonis

    mbenonis Wireless Guy Administrator

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    With due respect, I tend to disagree with your diagnosis of the problem. I find it hard to believe that an insulated antenna being near a body could cause the transmitter to fail - perhaps the pack got moisture in it? That would be a much more likely cause of failure. In terms of the actual effect of the body on a radiating element, the main effect will be an unpredictable* change in the radiating pattern of the antenna due to the impedance of the body.

    *Well, it's predictable, but you'd need a very accurate model of the body and a supercomputer to compute the effect of it on the antenna. Plus a model of the room and everyone else in the room.
     
  12. avare

    avare Active Member

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    Transmitter goes intermittent. Antenna is against moist body. Middle of performance. I move the pack and antenna to between the undershirt and top shirt in the same location. Problem solved.

    Andre
     
  13. mbenonis

    mbenonis Wireless Guy Administrator

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    What model bodypack was this, and was it in a condom or other protective sleeve? My best guess is that by moving the pack, you reduced the amount of moisture getting into the pack (the shirt would absorb some of the moisture). If you did it at intermission, that would give it a chance to dry out a little bit too.
     
  14. avare

    avare Active Member

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    Sennheiser G2 (you didn't ask yet but) working in the 700 MHz band.
    Yes, I was practicing safe sound.
    See above. The pack was protected.
    The timing was as follows:

    1. Signal goes bad while actor is on stage.

    2. Actor comes off stage and immediately comes over to wireless world.

    3. I inspect setup, move as detailed above and check signal on receiver meters. It looks good.

    4. Get A1 on intercomm to PFL mic. FOH is getting a good feed.

    Time from 2 to 3 was about 45 seconds. The A1 had another problem to work on and was delayed getting back to me on the intercomm.
    I know, hard to believe. Two problems in one performance.;)

    It's funny, I told the actors how to carry the packs, but they didn't pay attention. Once they realized that their lines might not be heard, they listened to what I told them.

    On another wardrobe related incident, I had carry pockets made for all the transmitters for actors who could not place transmitters in their pockets etc. The actors as a whole rejected the idea and just clipped them on their backsides
    wherever convenient. The cast as a whole when watching the archive video and seeing the LEDs shining on their backs. Especially embarrassing in the night scene illuminated all with R68 gels! Funny, once again people had to ignore professional advice and screw up their performances before listening.

    On a serious note, the OP asked if people have had problems with antennas touching skin. I have. I happen to be the only poster here who has. That does not diminish the fact that I have. The OP (or his wife) can decide which way they choose to go.

    Andre
     
  15. avkid

    avkid Not a New User Fight Leukemia

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    After seeing green lights shining through dancer's costumes for several years I finally had the idea to tape over the LED light.
    -
    Unrelated, sort of.
    I remember once asking the boss(who was in the show) what color the light was on his pack- "I don't know, I'm color blind.
    (for the average business manager this is isn't a real big deal I suppose)
    -
    The interesting part is that he is one of the best photographers I know.
    He actually gets credit in the newspaper for our publicity photos, which is unheard of.
     
  16. Grog12

    Grog12 CBMod CB Mods Premium Member

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    As the OP I asked for clarification which you've provided.

    Having checked into this situation farther...were they the rigid or floppy type antenna? As I've only heard of problems with one type ( the floppy) which is opposite of the type I typically use and the one's being used in this performance.

    As neither my wife nor I are mixing this show..we don't care. I was looking for information on the subject. I actually saw the show last night...and honestly wheter it was a floppy atenna touching the skin or not, nothing could help the sound on that show as it was so bad.

    Andre/avare feel free to post in our new members boards as a shameless promotion of yourself and so we can know who you are and whatcha do. We're generally pretty chummy around here...except charc
     
  17. avare

    avare Active Member

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    I'm glad I could help.

    It was the floppy type of antenna.

    Technology is always losses to lack of skill and proper planning.

    Will do.

    Andre
     

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