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Telex BTR-24 Antenna Question

Discussion in 'Sound, Music, and Intercom' started by RedmonwantsEOS, May 29, 2009.

  1. RedmonwantsEOS

    RedmonwantsEOS Member

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    Hello All,
    I have a question about Antenna Wiring for the Telex BTR-24 2.4 GHz Intercom Base Station. Our high school recently got this base station as part of a new sound system that was installed in April (that's another story...) The main installer (Part of the County's Audio-Visual Services) ordered 2 Antenna's to use with this station, with one backstage and one located near the control booth. He split both the Tx and Rx Antenna leads from the base station. Nowhere in the manual is this multiple antenna method mentioned. They also replaced the RP-TNC connectors with F-Coax connectors. I'm just wondering if this is proper/correct. Does anybody have any experience with this base station and the associated antennas?

    Thanks!

    -Andrew

    Adapting from RP-TNC to F to BNC:
    [​IMG]

    BNC T for Booth and Backstage Antennas:
    [​IMG]

    One of the Antennas:
    [​IMG]
     
  2. mbenonis

    mbenonis Wireless Guy Administrator

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    Sorry to be the bearer of bad news, but this looks like a bad install all the way around. First, while there is no inherent problem with using two receive (or transmit) antennas, you need to use the proper splitter - that is, one that maintains proper impedance matching. In addition, at 2.4 GHz you need REALLY low-loss coax cable - TV cable, which is what the county used, won't cut it. I'm not going to say it won't work - it probably does - but I will say this is far from the optimal install.

    The first question I have for you is how well does it work? Do you get coverage back stage, in the house, and in the booth? Do you get dropouts, or do things seem to be working OK? If the answer to these questions is that it does seem to work, my advice is to just leave it well enough alone (and if it breaks, the county can fix it). If the answer is you have reception problems, we'll take it from there.
     
  3. RedmonwantsEOS

    RedmonwantsEOS Member

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    We actually have not had a chance to give it a true test yet because the County still hasn't connected the Antenna near the booth yet. I was running lights+sound for a ballet this weekend and REALLY needed to use the system, and it wouldn't work with just the antenna backstage. So I had to take the Base Station out of the rack and just connect the booth antenna, which worked quite well, even backstage.
     
  4. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Looks like we have a Shure paddle not connected either, and if that window in the picture points towards the stage we have a horribly oriented antenna...

    In theory the F connector is good to a couple of GHz, mileage varies because F connectors vary so much.

    Multiple adapters work OK in audio, alright in video and just run up the loss quickly in RF.

    Using T pieces is ok in some coax applications and at some points, RF and with long cables on each leg are both missing from the list of OK times.

    OK, so your booth is higher right? That will be a part of why you got reasonable performance using that antenna, but I would hazard a guess that you might achieve similar results with the stage antenna direct connected to the base station too...

    OK, so RG6 does not have a rated loss figure beyond a Gig. At Gig it's losing about 6.5 db per 100 feet (US manufacturers using them funny numbers again.)

    So if we look at the transmit part of the base for a moment, we'll say there's a nice power split at the T (I'm in fantasy world now), there's 3 and a half dB gone, and you're going to have at least 30 metres, perhaps even double that between stage and control room. Add in 6.5 dB. There's 10 dB gone. You're now looking at a tenth of the power getting to that antenna versus what happens when it's direct connected...

    If you could give us a rough length that the cable is running between base station and each antenna as well as broad dimensions of the space you're trying to cover and it's construction, any walls to note etc. we'll be in a much better position to make educated guesses about what might work in your circumstances...
     
  5. GreyWyvern

    GreyWyvern Apollo Staff

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    Looking at the pictures, it looks like the used crimp-on fittings instead of commpression fittings. I would venture a guess that they did that because they didn't have the commpression tools needed to do the job correctly. So they used cheap crimp-on F connectors instead of compression BNC (or F) connectors as they should have done. (Once again, be sure to have the right tools for the job!) Ever notice that when the cable company is using existing cable when installing, they cut off crimp-on connector and replace them with compression fittings? They do that for a reason. The compression fittings are a higher quality connector for several reasons. They provide a better cable-to-connector connection, they are more robust, they have less loss, and they don't crush the di-electric foam in the cable and impede the signal like the crimp-on do.

    Each time an adaptor is introduced, a certain amount of loss is added. The 'T' needs to be replaced with a proper splitter. Also, if they had to wrap a connector in e-tape, (RED FLAG) they screwed something up there.

    One more thing, RG-6 may not be the correct type of cable. There are many types of coax for many differtent applications. RG-6 Just happens te be the most common due to the cable industry. It is important to match impedances.

    Hope this helps.
     
  6. mbenonis

    mbenonis Wireless Guy Administrator

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    It is, but only when it matters. :) For instance, in wireless mic receiver systems, 75 Ohm cable will not make a significant difference in performance, and its loss at 700 MHz is MUCH better than RG-58 or even some flavors of RG-8. At 2.4 GHz, through...I'd be using LMR600 or better cable simply for loss reasons, especially for runs more than a few feet.

    As a rule of thumb, impedance matching is important when you are transmitting, not receiving (at least as far as the average theatrical wireless system is concerned).
     
  7. RedmonwantsEOS

    RedmonwantsEOS Member

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    The Shure Antenna was not connected in that picture because that photo was taken before the entire installation was done. And yes, they are pointed AWAY from the stage, we're working to get that corrected before graduation on June 20th =p.
    Yes, the booth is higher up than the stage.
    Between the base station and the antenna mounted near the booth, I'd say there's about 25' of coax (much of it coiled as excess) and between the base and the backstage antenna, we're looking at 150 to 200 feet of coax cable :/
    It is about 70 feet from the booth to the front of the stage. The Auditorium is 89 feet wide exactly at its widest. Backstage is about 87 feet wide total, with the actual opening 48 feet wide. Backstage is about 28 feet deep.
    And yes, the F-connectors on the Antenna leads fail. One of them actually fell off the cable yesterday. =p
    I got a chance to talk to them again yesterday. They said the reason they have not finished connecting the antennas is because they're getting some amps for the antennas. I shudder to think what kind of amps they are going to use for 2.4 GHz WiFi Antennas...
     
  8. rwhealey

    rwhealey Active Member

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    If putting the antennas in the booth worked to cover the whole facility, you could just leave it like that.

    Simple is good.
     
  9. Chris15

    Chris15 CBMod CB Mods Premium Member

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    They make amps designed for use in WiFi at 2.4 gig and so one could quite easily be getting something of that nature...
    One should check the legal power limits for emission though...
    It is also possible that AV really meant splitters and amps...
     
  10. mbenonis

    mbenonis Wireless Guy Administrator

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    I would hope they get 2.4 GHz amplifiers, because TV distribution amplifiers aren't going to work terribly well...
     
  11. Chris15

    Chris15 CBMod CB Mods Premium Member

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    But some of the stuff for satellite distribution might...
    It was more that the OP was seemingly worried about these amps and I'm trying to convey that they might in fact be the right thing for the job...
     
  12. mbenonis

    mbenonis Wireless Guy Administrator

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    True, very true.
     
  13. themuzicman

    themuzicman Well-Known Member

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    I'll assume you're the Loudoun Valley that's right down the street - I've had to deal with the Loudoun Co. team installers - Don't trust them for proper anything, my old high school's sound system wasn't even wired fully when they finished the install, no matter how much they claimed it was done - make a long story short, they just re did the entire system, and the school's only been open 4 years.

    Can't trust Loudoun County for anything.
     
  14. the1rmdman

    the1rmdman Member

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    I don't have an answer for your question but a question about the Telex BTR 24 system. I can't seem to find anyone who has used it. I'm looking for a wireless intercom and want to know how well these work. Any info or a link to some reviews would be great.
     
  15. the1rmdman

    the1rmdman Member

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    So I guess nobody has used the Telex BTR 24 system. Ok, if any one ever does, please let us know if they are any good.
     
  16. RedmonwantsEOS

    RedmonwantsEOS Member

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    Sorry for not replying sooner, been busy with college.
    The BTR-24 System is GREAT when it is installed properly. You don't even technically need to have a basestation for a basic, low range setup. I also like how, with a basestation, you can create a hybrid wired/wireless system, just by using Cat 5e cable.
     
    the1rmdman and (deleted member) like this.
  17. Anonymous067

    Anonymous067 BANNED USER

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    Disregarding the hijack that took place, what ever happened with the OP at his facility?

    I'm curious to hear what happened! Please keep us posted!
     

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