Advice needed about multiple antennas and radio wave behavior.

Discussion in 'Wireless & RF Design' started by Lambda, Mar 5, 2011.

  1. Lambda

    Thread Starter New Member

    Feb 28, 2011
    Hi everybody. I happen to know next to nothing about radio, so I thought I would ask this here.
    I have an FM transmitter that I need to get working in a theater space. Its purpose, is to transmit stage directions to receivers worn by stage hands. The transmitter is a Williams PPA-T17 auditory assistance transmitter. It advertises a range of 300-500 feet, but I have found through testing that this is not true, in the least. I'd say that in ideal conditions, it can transmit a clear signal 20 feet, and a staticy signal 50 feet line-of-sight.
    The frequency is 72.9 mhz.
    Perhaps one of the largest problems that I have here is its inability to transmit through walls. The antenna is located on one side of the stage in the auditorium. The signal must be audible on the other side of the stage, in the hallways on the other side of the wall surrounding the stage, and in the green room, across the hall from the stage. A drawing is included here.

    The antenna that is with it is a co-axial cable, with the last 10 feet encased in a sort of steel mesh, and in the last two feet of this line, the shielding strips away, leaving the signal-carrying center conductor encased in insulation, inside the steel mesh. I'm assuming that this part of the antenna radiates the signal.

    The major problem is that it won't transmit through any of the walls, which are concrete, and is not very audible on the other side of the stage. The addition of a long wire antenna to the receivers helps a little bit, but not much.
    To remedy this, I thought that I could have three extra antennas, connected to the transmitter by means of co-axial cables (numbered 1, 2, and 3 on the drawing).
    My questions are these:
    How can I build additional antennas? It specifies a 75Ω antenna.
    To connect the antennas to the transmitter, can I just use co-axial splitters, or do I need to build some sort of active distributer? Maximum cable length is stated to be 400 feet. But then again, they claimed the range to be 300 feet, so who knows.
    And is there anything else I should know?
    All I know about this thing came from this PDF:

  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010

    Remove the steel mesh from the end where it 'surrounds' the center conductor.
  3. Lambda

    Thread Starter New Member

    Feb 28, 2011
    Thanks for your reply.

    I'd thought about that. It is obviously part of the antenna from the factory, but I have no idea what purpose it serves. I'll see if I can get it off when I go in on Monday, but I think that the only way would be to cut it off, and I don't want to cause too much damage to the antenna.