The solution is to consider how far the antennas are from the receivers (the coaxial cable connecting them loses signal, so the longer the cable the more loss you have to compensate for) and how far the antennas are from the transmitters. If your antennas and receivers are both near the side of the stage or altar area, with relatively short coax cables, you probably don’t need RF amplification (and maybe not even directional antennas). In fact, you might need a pad. Pads reduce the signal strength, and while that might seem like a counterintuitive solution to RF problems, sometimes that’s exactly what you need to make the receivers happy with the signal strength. Keep in mind that interference sources will be reduced, too, with a pad.As if all that isn’t enough to consider, we also have to actually pick good frequencies to use. If we’re just using one system, it’s basically as simple as looking for a clean channel on the receiver and then using it. However, things get hairy when multiple systems are in use. The problem is that transmitters will interfere with each other in a process called intermodulation distortion (IMD, or “intermod”). This interference creates additional RF products in the air that weren’t there before, and those RF products may end up landing on other frequencies we’re trying to use. So, RF coordination involves considering not just that every system needs a clean frequency, but that the intermod products between each system and each other system can’t land on frequencies already in use. It only takes a modest amount of wireless channels in use before you have a few thousand frequencies to worry about. How do we deal with intermod? There are three keys: 1) Good RF coordination. Some of the major wireless product manufacturers offer free software you can download, and there are also commercial products such as the Intermodulation Analysis System software from Professional Wireless. 2) Keep transmitters physically separated as much as practical. Intermod gets worse as they get closer together, since it’s a function of the transmitters causing distortion products in each other. 3) Use low-power transmission if your products give you the option. Sometimes you really do need to use the high-power setting, but unless you’re absolutely sure you need it, low power is often better. It allows more channels to operate happily together and is less likely to overload the receiver if you have lots of RF gain involved in your system. Plus, it leads to better battery life, and that’s a nice side effect.Even though we have really just scratched the surface, I hope this provides a good starting point for you. The major manufacturers have some good technical papers available on their website, as well as free RF coordination software; I highly encourage you to read and experiment. RF can be a bit mysterious, but with a little education and experimentation, it can be a lot more reliable. Happy wireless!
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