The wonderful world of wireless technology provides an abundance of benefits to any production or venue. The ease and freedom of in-ear monitors and wireless microphones have become an industry standard. Of course, it also provides its fair share of technical obstacles that can be quite challenging if you don’t have the knowledge or the wherewithal to tackle them. Without the proper attention, your production can be plagued by signal drop-outs and terrible static or feedback. What are the best ways to avoid these pitfalls? In this article, we want to take a look at some common problems wireless set-ups can have and how to avoid them.
Don’t drop out kids!
We’ve all been there. We’re enjoying a great performance or engaging lecture and all of a sudden the sound cuts out taking you out of the moment. It’s akin to a scratched CD or a bad wifi signal. There is not much worse than a live performance interrupted by signal dropouts.
Many factors play into why a wireless signal may be dropping out. Multi-path interference is one predominant factor. This happens when portions of RF energy arrive at the receiver’s antenna at different times. Radio waves like to travel in straight lines and when they need to get around a corner they bounce off and around surfaces. These surfaces either reflect or absorb the waves causing them to arrive at the receiver at slightly different times resulting in dead spots or dropouts. In addition, with every surface the wave bounces off, it flips the polarity 180 degrees.
When those sound waves mix in the antenna, they almost always cause signal cancellation. This is called cross-polarization. This is common at indoor venues where there are many surfaces to bounce off. It’s particularly problematic with wireless microphones which are in constant motion during a performance.
Clear Path Solution
The simple solution to this dilemma is to make sure there is a clear path from the transmitter to the receiver. As much as you’re able to control it, make sure there are no obstacles in the way. That would include the bodies of, say, audience members or any metal trusses or barriers. Set the receiver above head level and make sure you walk the stage or performance area with the mics monitoring your RF signal. You want to make sure your signal is covering the geometry of the performance space.
Multiple Antenna Solutions
Most systems use a diversity microphone receiver to reduce the interference caused by multi-path. They typically sport two antennas that have different perspectives and use a switching function that discriminates between the relative strength of two signals. This reduces the potential of a dead spot in the signal. However, this can introduce another issue. If the receiver is switching rapidly between two poor signals, it can produce a “swooshing” sound and quick dropouts. To remedy this you can either try to relocate your receivers to better cover the relay area. Better still, install a good remote antenna system. The RF Venue Diversity fin is a polarization diversity antenna that will eliminate cross-polarization dropouts.
Also, make sure you don’t have any antenna farms on your hands. Large clusters of whip antennas will steal power away from each other and severely affect the clear transmission of your signals. Antennas should never be closer than 6” apart and better if they are at least two feet apart. Using a distribution box or directional antennas will help to solve this issue. RF Venue systems are designed to consolidate many wireless receivers. They combine antennas with the goal of using one single antenna in the place of many. They also declutter your racks and optimize wireless performance.
Rise above the noise!
We are constantly swimming in a sea of radio waves from a multitude of sources and your wireless signal is working hard to make its way past all of them. Everything from computers, video walls, LED lighting, power supplies, and cell phones are all mingling in the same space to create what has been labeled the “noise floor”. Even natural radiation generated by the earth contributes to this “floor”. We can all probably recall a time during some production or another where we were asking “where the heck is that noise coming from?”
It is essential that any wireless system maintains a high signal-to-noise ratio to stay above this ever-present ambient noise environment. The best thing to help with this is to keep a short distance between the transmitters and receivers. An RF spectrum analyzer is extremely helpful in monitoring your noise floor. If your venue has a higher than normal noise floor, you might want to consider a local field antenna such as RF Venue’s Spotlight antenna. This antenna can isolate reception and decrease the amount of noise entering the signal chain. Their Band Pass Filter can also dramatically reduce your noise floor by 6 to 15dB. It is also recommended to use top-quality, 100% shielded coax cables to reduce the ingress of stray RF into your system.
Don’t get it distorted!
The wireless landscape continues to evolve with the growing amount of devices relying on wireless transmitting all trying to compete for less and less space on the available spectrum. Because of this, intermodulation distortion (or IMD) is an ever-present issue that engineers and techs must handle. IMD happens when two or more signals pass through a non-linear device such as a diode or an amplifier. IMD is directly related to harmonic distortion. So, when you have too much you get less than optimal clarity and in extreme cases just intolerable sound.
The best way around this is by meticulously selecting frequencies to force the IMD to happen only at frequencies we don’t care about. This is accomplished using software tools such as Shure’s Wireless Workbench. However, in order to get the best solution from these programs, it requires providing them with the best possible data. Using a dedicated spectrum analyzer like the RF Explorer Pro Audio Edition goes a long way in eliminating unwanted IMD.
Employing some of these solutions will go a long way in improving your wireless performance, not to mention save you thousands of dollars and an undue amount of stress. But this is just the tip of the iceberg when it comes to optimizing your wireless system. I hope these tips provide you enough to get your issues sorted, but if you need more help, I highly recommend checking out RF Venue and their dozens of blogs. They cover pretty much anything you need to handle the ever-increasing complications posed by the wireless world. We are big fans of their wireless solutions as evidenced by the recommendations made in this article. They have a multitude of incredibly helpful products that we currently have in stock. If any of these products would be beneficial to your venue or production, give us a call and we’ll be happy to get you set up!