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Wireless 12tx Radio Mic Distribution

Discussion in 'Sound, Music, and Intercom' started by howartp, Nov 2, 2008.

  1. howartp

    howartp Member

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    Hi,

    We’re looking at enhancing our Radio Mic provision at our annual Pantomime plus other events.

    Currently we own 1 Trantec VHF lapel and 1 Trantec VHF handheld, plus we borrow random sets from contacts in the area including two Sennheiser UHF G1 (100Series?). However we have great problems with them interfering with each other so we’re looking at getting a whole new set of 12. I’m pretty much committed to the Audio Technica ATW-3110A/P1 sets, but I’d like to run them through a distribution system with one pair of Antennae. (I’ve simplified our situation to avoid unnecessary confusion, hence why we’re committed to this model or something of very similar price – around £310 each)

    From my current research including speaking to a local Audio/Visual company, I’m thinking I need four ATW-DA49’s (4:1 UHF Distribution Amp) to run the 12 sets off one pair of antennae; I firstly thought I only needed three, which would give me 12 outputs, but I don’t think there’s a loop through? So I’m thinking the first DA49 would have the Antennae connected to its A/B inputs, and three of its A/B outputs would be connected to the A/B inputs on the other three DA49’s? (Thus running the distribution in parallel, rather than serially linking them one to the next?) I’ll probably run separate power packs for each DA49 then I don’t lose everything if one goes. I’m also thinking of getting the ATW-A49 extended Antennae to bring them outside of the (wooden) rack.

    Can anyone confirm that this all looks correct?

    Cheers,

    Peter
     
  2. mbenonis

    mbenonis Wireless Guy Administrator

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    Occupation:
    Radio Engineer
    Location:
    Washington, DC
    That would definitely work, but it might be costly. A couple of questions might reveal a few other options:

    - Where will the receivers be, and where will the antennas be?
    - What type of antennas do you plan to use? LPDA (Shark Fin)? Dipole?
    - What kind of coax cable do you plan to use?
    - How much power is currently in the UHF band where you are? TV? Other things?

    If you can get the antennas close to the stage, and if you use gain antennas (like an LPDA), you might be able to get away with using a passive RF splitter rather than an active one, thus saving you a bit of money.

    By the way, it is very important to coordinate your frequencies when you set the units - and preferable to do it manually. Please see some of my other posts on how to do this using IAS or SIFM.

    Mike
     
  3. howartp

    howartp Member

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    Hi Mike,

    If you have a look at www.oakworthmethodists.org/Panto_AV.pdf it will help me explain.

    We're currently debating where the receivers will be best placed, after reading other threads on this forum. They were going on a shelf in the Audio Rack, together with the rack-mounted DA49s - this would give the Audio tech sight of them should there be an issue. However it is probably better for myself (the Media/Film tech as I've called myself in the diagram) to have sight of them as it's me who will be responding to any issues. So we're thinking of having them on the walkway somewhere. Dare I ask whether it is better to have a long antenna cable and short audio cable, or short antenna cable and long audio cable?

    We're looking at the ATW-A49 'UHF Wide-band Directional LPDA Antennas', purely in order to keep everything with the same manufacturer. Is this sensible?

    Coax cable I've no idea, but my cousin works in A/V installations, so he will probably just get me the right stuff without anyone noticing. :) If you want to tell me what I should be using, I'll suggest it to him. (He won't generally advise on A/V because he works in installs, not sales - he can only tell me what he installs most of, not which is best because of x, y or z)

    I've no idea about what UHF is in the area, but I've never knowingly had an issue with external interference due to other channels; there's no TV broadcasting stations nearby, but who knows what signal is actually flying around us.

    What sort of cost savings would the passive splitter vs active DA involve - I don't want to save £100/$200 by going passive, then have to fork out another £400/$800 to get active later. It won't go down too well with the treasurer, who happens to be my father. Also we've got a kind of agreement within our local churches that will save us some money if we get the kit now (and share it) so it might well be better to get the active stuff anyway.

    24 hours ago, I was vaguely familiar with the need for mod-free frequencies and have a set suggested by Audio Technica which I'm thinking of using. I went to bed last night, having read this and another similar tech forum, fully versed on the workings of frequency mathematics and the need to carefully calculate my frequencies, using various software applications available from various manufacturers! So thanks, but I'm sorted on how to go about that bit of it. :)

    Peter
     
  4. mbenonis

    mbenonis Wireless Guy Administrator

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    Occupation:
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    Absolutely better to have a long audio cable and a short RF cable.

    Honestly, it doesn't matter what manufacturer you use (unless it's an active antenna; then you need to worry about supply voltage and current).

    Remember that TV and video use 75Ω cable, and RF and radio use 50Ω cable. It's probably a better choice to use 50Ω cable for this (though honestly it won't make too much of a difference). For runs under 10 feet, use RG-58; over 10 feet use LMR-240 or LMR-400.

    I don't know much about the UK's RF spectrum, so you'll probably need to get a local guy to figure out what TV channels are out there and who else might be using the band. I also don't know where it is legal for you to operate.

    Active will probably be better, if you can afford it.

    Excellent. Let me know if you have any more questions.

    Mike
     
  5. waynehoskins

    waynehoskins Active Member

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    Location:
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    For a long run I'd even strongly consider hardline, since we're talking about above 450 megs, and 400 is, I believe, 3 down per 100 feet at 432.

    My preferences:
    1. Get receivers and antennas right close to the transmitters (just offstage)
    2. Failing that, get antennas close and use a really low-loss feedline

    Audio frequency loss down audio cable is insignificant. At RF, loss down cable is significant, especially at UHF.
     
  6. howartp

    howartp Member

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    Hi Mike,

    Since speaking to you we've been given a £3,000 grant that we knew nothing about before it came, so we are definitely going for the active DAs! We've actually upgraded to to the DA860's rather than the DA49's as they include a loop-through output for daisychaining them.

    In total we'll have 16 Radio Mics inc 2 handhelds, to give us various options and spares. (We're only purchasing 3 DA860's which gives us 12 outputs)

    We have a license for using Channel 69 so we're ok that way, unless and until they mess around with the channels in a few years.

    Thanks for all your help.

    Peter.
     

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