Interference Prevention: Managing Complex Venue RF Challenges
Eliminate RF Interference with Proper Combiner Selection and Setup
Today’s complex shows and venues come with some interesting challenges. Multiple in-ear monitor (IEM) systems, hoards of wireless microphones, complex wireless intercoms, wireless stage controller systems, not to mention audience wi-fi, in-building cellular and first responder RF along with who-knows-what-else systems that may be present. All of these signals can add up to a big RF mess if not handled correctly.
One piece of technology that aids in combating interference in crowded venues is the RF combiner. In complex situations, a venue can easily have several transmitters, all operating on different frequencies in the same band. For example, a typical production may have several UHF intercom channels, along with several in-ear monitor transmitters, all competing for limited antenna space. If individual antennas are used in a limited area, the coupling between antennas creates intermodulation (IM) interference between the transmitters.
Choosing the Right RF Combiner: Passive vs. Active Linear Amplifier Systems
Combiners solve this problem by combining the signals from each transmitter into one output that feeds a common antenna, with special care to reduce IM signals generated in the process. This is not as simple as it might seem. There are passive combiners that can sum a low number of signals together, but they introduce substantial loss in the process. In addition, such simple combination circuitry can still introduce serious IM signals into the antenna, depending partly on the construction of the transmitters being used.
The best combiners use highly linear amplifiers, along with specialized combining networks, to produce high-quality, low IM outputs. When selecting a combiner, it’s important to look at the IM specifications to ensure that the unit will meet system requirements.
Our Tips for Minimizing Intermodulation Issues
Let me give you a few practical tips:
Never cascade combiners: Don’t take the output of a combiner (even a simple two port combiner) and put it into another combiner. This virtually guarantees a host of IM problems, not to mention the potential of damaging the combiner. A “hidden” version of this problem: Don’t connect a combined output (such as a two channel intercom or IEM system) to a combiner input. Always use the split output of these devices when using a combiner. Consult the product’s instruction manual for details.
Use the lowest power possible. Lower output power from a combiner channel comes with lower IM products. If 50 mW works reliably for your IEM, then there is no good reason to use 250 mW.
Check your combiner’s manual for tips on minimizing IM products. Many combiners have certain ports with more isolation than others. By selecting the correct input ports, you may be able to minimize IM products for the most troublesome frequencies.
Keep antennas separated as much as possible, especially antennas connected to higher power devices, such as in-building cellular and first responder systems.
Use frequency coordination software. If there is no one competent to do the coordination task, hire it out. There are several professionals who specialize in frequency coordination for complex venues.
Once the system is installed, conduct some “war games” to suss out any issues: Turn everything on and have a look for problems. Get a good spectrum analyzer and search for troublesome IM products. More importantly, check all of the RF systems to make sure they are working properly without interference.
Investment in Quality: Why Professional RF Equipment Pays Off Long-Term
As always, high-quality equipment and good workmanship during installation go a long way to a great system. The investment made in doing it right will pay off in trouble-free, reliable operation.
At RDG, we’re committed to providing the best RF hardware solutions. Don’t let Intermodulation issues disrupt your live events. Stop wasting time putting out fires. Get reliable intermodulation solutions for your live event venue. Your audience deserves the best.
We offer engineering consulting, as well as install-ready, professional-grade RF products.