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Extending wireless antennas w/o distribution system

Discussion in 'Sound, Music, and Intercom' started by jkowtko, Apr 26, 2009.

  1. jkowtko

    jkowtko Active Member

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    (I know I'll catch from flack for this, but --)

    Looks like the FCC ban deadline is dragging out, and with our community theater finances worse than ever due to the recession, not really any chance of replacing our AKG WMS80 units in the near future.

    So, for now I have all of the receivers up high on a wooden rack in the sound booth, a mere 30-40 feet from the stage, but I think the RF is still pretty weak.

    The WMS80 units do not have detachable antennas, therefore no antenna distribution system options in the product design. They're not cheap anyway, so probably out of the question.

    So short of moving the receiver rack away from the sound booth and closer to the stage, is there a way that I can effectively move the antennas only out closer to the stage?

    I don't mind pulling apart the receivers and doing a bit of surgery here -- these units are old, and I have several backup receivers sitting in storage to use in case I make some fatal mistakes.

    Thanks. John
     
  2. Footer

    Footer Senior Team Senior Team Premium Member

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    Doubtful. If done wrong you could change the physical antenna design and actually make the problem worse. If you are having problems with 40' of airspace, your not going to get much better moving the antennas without putting them center stage. Buy a 100' snake and put the receivers onstage. You don't actually need to see the little lights.
     
  3. mbenonis

    mbenonis Wireless Guy Administrator Premium Member

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    Yeah, I think the best option is to move the receivers closer to the stage in your case - modifying the receivers to remote the antennas isn't a terribly good option if you don't have an electronics and RF lab at your disposal.
     
  4. Anonymous067

    Anonymous067 BANNED USER

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    +1 I agree.
     
  5. waynehoskins

    waynehoskins Active Member

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    Yeah, just move them. It's probably better that way anyhow.
     
  6. FMEng

    FMEng Well-Known Member Fight Leukemia

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    You might find that putting the receivers in a different spot works better. For one thing, the metal top of the receiver acts as a ground plane for the antenna, which means the antenna doesn't pick up quite as well away from the back of the receiver. Orienting the receiver with its front toward the mics to take advantage of the ground plane does sometimes make a difference.

    If you are using lav mics, the transmitters are usually on the back of the actors. Put the receivers at the back of the stage so that you don't have human flesh between them and the transmitter, most of the time.
     
  7. museav

    museav CBMod CB Mods Departed Member

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    Not to give you flack, but just to be realistic, I believe those units operate at 710-746 MHz and while the 698-806 MHZ ban has not yet been enacted, my personal belief is that this is primarily due to the fact that some analog broadcasters are still operating in that spectrum and the ban proposed would thus have conflicted with the extension of the DTV transition deadline I would not be surprised to see the ban enacted not long after the June 12 transition date (unless that date is delayed at the last minute yet again), so whatever you do for those units may be a short term, as in a couple of months, solution.

    Probably the last thing you'd want if the ban is enacted, or as the licensed users begin using their spectrum, is a device operating in that spectrum for which the antenna has been modified.
     
    Soundguy1 and (deleted member) like this.
  8. dramatech

    dramatech Well-Known Member

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    generally speaking, without and electrically amplified antenna, the loss of signal in a long length of coax cable will probably be greater than the loss of signal in free air/line of sight. I went through this execise a few times a couple of years ago, and the math simply pointed out the futility of doing as you propose. The best bet without amplified antenna distribution is to get the receiving antenna as close as possible to the transmitting antenna.
     
  9. Chris15

    Chris15 CBMod CB Mods Premium Member

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    I'm sorry, but I feel your numbers are flawed. Let's look at some sums; Free space and coax losses increase with frequency. We'll use 900 MHz for the sake of comparison, it being a number on the data sheet I have handy.
    For the sake of comparison, we'll take an unrealistic length of coax at 100m.
    @900 MHz, RG58 (ZCG Scalar data sheet used for this) loses 35 dB.
    The free space loss for 100m at 900 MHz is a mere 71.5 dB.
    That's more than 35dB difference, meaning we have 3160 times more power when using coax.

    So please explain to me why the coax is more lossy?
    Amplified antenna distribution is a very broad statement, what do you mean by it?
     
  10. airkarol

    airkarol Member

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    Send Phil Ladue a message. His username is avkid. We were working on something similar in his theatre last year, he'd know more about what was going on with it.
     
  11. midgetgreen11

    midgetgreen11 Active Member

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    I completely disagree with this, as the man who taught me everything I know about sound, working for a Rhode Island TV station.... used to say "The more money you spend on wireless, the closer you'll get to a $25 XLR Cable."
     
  12. museav

    museav CBMod CB Mods Departed Member

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    I agree with the quote but I think there perhaps is some misunderstanding. The comparison being addressed was for extending the antenna and the resulting signal losses in the length of antenna coax to remote an antenna versus the RF losses for the same distance in free air. That is totally different than talking about a wired mic, which typically does not involve coax.


    I am a bit confused with this. The first sentence seems to argue that the losses in coax would be greater than in air, thus extending an antenna would incur greater losses. But in recommending trying to get the receiving antenna as close as possible to the transmitter, the last sentence seems to suggest doing exactly that. Was the last sentence actually suggesting moving the receiver itself, not the receiving antenna, as close as possible to the transmitter(s)?
     
  13. jkowtko

    jkowtko Active Member

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    I am interested in figuring this out. We just upgraded to new systems with detachable BNC antennas, working two frequency bands, 500-530, and 650 - 680.

    The wireless rack is about 30-50 feet from the actors on stage, but unfortunately directly at house center, so Tx on the actors back will have to go through their body. Something as simply as putting the mic on their side or front or having them turn 45 degrees when speaking, makes a difference -60 to -70db and having solid signal.

    So, two reasons for moving the antennas out from the back of the rack-mounted units is to (a) get it out of the rack, (b) to significantly widen the angle of attack on the stage.

    With a 25' cable on each antenna I can get them 20-30 feet from the actors and close to a 90 degree triangulation on the transmitters.

    Wouldn't the increased angle on the two antennas be a significant benefit even if the coax/air gain/loss is a wash?

    Lots of cable seems like it would be a lot cheaper than an antenna distro system.

    Thanks. John
     
    Last edited: Mar 9, 2010
  14. SHARYNF

    SHARYNF Well-Known Member

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    As has been mentioned before MOVE THE RECEIVERS TO THE STAGE, this will make a major difference in the operation, they can be to the side or rear but especially on the less than super expensive wireless systems putting them on the stage works best. They really were designed for freedom of movement on the stage vs transmission. Angling the antenna helps and making sure that the antennas do not over lap one with the other.

    Sharyn
     
  15. jkowtko

    jkowtko Active Member

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    Moving the receiver rack is my last choice, simply because we have no A2 and therefore no way to monitor the wireless if it's not in sight of the Sound Op. We do have some closed circuit cameras, so eventually I could try this if nothing else works.

    I did turn the rack (took some doing) to face back directly to the stage ... it was at a 60 degree angle before. This gave the receiver-mounted rabbit ears as slightly better angle on the transmitters. I can't say if it helped or not.

    I'm also working with the actors to get the mic packs front and center whenever possible. The AKG WMS450 systems have tiny transmitters, almost as small as the Senn 5012, so I can hide them almost anywhere :) They don't seem to like transmitting through human bodies, and they don't seem to like being pressed hard up against a human body. It can't be too hard to get this figured out with the help of the house costumer ...

    I did talk with the AKG tech at length, on the options of antenna extension. It looks like the passive rabbit ears on the back of the box carry only 1db of signal strength at best, so using a reasonable RG58 cable you can only add a 6 foot length of cable before rendering the signal unusable. (RG213 cable might double that if the signal loss rating is lean enough, but for several times the price of RG58 not worth it at our theater.) So ... I'm going to try tonight pulling the rabbit ears off one of the receivers and place them a few feet out from the rack and apart, to see if I get any RF improvement.

    I also understand from the tech that some frequencies will fare better than others, because of -100db or less noise that is present but I cannot see on the receiver RF meter, may actually be interfering with transmission. So I have my stack of IM-compatible frequency set printouts with me and am going to try different frequencies with our worst channels to see if this has any noticable effect. If anyone in the SF Bay Area has an RF scanner and is willing to run a scan for me, I'll buy lunch ;) What I'm seeing is somewhat different than what the FCC claims is out there.

    If I can't obtain sufficient quality of signal with these other methods then it will be moving the rack or spend the $$ on the distro system. Or live with the occasional but annoying RF noise ... :|
     
    Last edited: Mar 10, 2010
  16. Morpheus

    Morpheus Active Member

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    I think it's supposed to mean that the more money you spend, the more you'll see performance as if you bought $25 worth of mic cable and moved the receivers closer.

    And jkowtko, unless you have to reprogram in the middle of a show (who does that?) you don't need to see the receivers... Just put a panel over the front if you're worried about someone messing...

    Also, the new sennheiser wireless are great - We just got 16 new units at my school, all rackmounted in a room behind the sound area, so to actuall access the racks themselves, i need to exit the balcony, and go into the projection booth... it's all good though, with the paddle antennas and distro systems, i can monitor the receivers over the network.
     
  17. SHARYNF

    SHARYNF Well-Known Member

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    In my experience the less expensive wireless units simply don't work well a distance from the stage. In addition in my experience you want the person who is putting the packs on the talent to have access to the receivers, there is very little need for the foh person to access the receivers. It is the interaction of pack and receiver that needs to monitoring and this is most likely NOT done from the sound booth.

    Again to each his own but IMO the reasons FOR by stage far far outweigh the booth placement

    Sharyn
     
  18. jkowtko

    jkowtko Active Member

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    For us it will be a 100 foot 16-channel snake. Which we have one I can use .. but again the other reasons cause me to not want to do this as a first choice. RG58 6 foot lengths are only a few bucks each. I could outfit all 14 of our channels for maybe $200 or less ... compare that to antenna distribution for $2000+

    battery warning -- one hour. Sudden RF interference vs mute ... and yes I can reprogram a receiver in about one minute if needed, in between scenes.

    Yes, like everyone says, spending the $$$ on the antenna distribution system will always be better. If you guys have a couple grand leftover in your sound budget please send it my way ... ;)
     
    Last edited: Mar 10, 2010
  19. jkowtko

    jkowtko Active Member

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    I am both. As I mentioned, no A2. Actually we have to have the actors put on their own packs. The backstage ASM is non-technical.

    Yes, again, if you have money, budget, can attract the right staff, great ... but this theater doesn't have that. And all one-person sound operations I've seen usually keep the receivers next to the console.
     
  20. SHARYNF

    SHARYNF Well-Known Member

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    Does not have to be an A2. Again just my experience but when I put on the packs I am interested at that point in what I am showing on the Receiver. from that point on, back at FOH I have no need to check the receiver, and If I had a problem I would then be back stage and would check pack/receiver. I know a lot of folks do put the receiver at FOH but IMO makes little sense. IMO it is a hold over from when folks saw wireless more for all around the venue than predominately from on stage

    Sharyn
     

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