Question: What is intermodulation distortion in a wireless system?
Answer: There are many papers, articles and blog entries written about intermodulation distortion (IMD). Almost all of these get into great scientific and mathematical detail to describe it. They will throw around terms like nonlinear circuits, 3rd order, 5th order, as well as mathematical equations such as f1+f2-f3, f1+f3-f2, f2+f3-f1. All of this is necessary information for engineers and integrators, but for most people who just want to know why their wireless system is not working properly, it is way too much information. They just want the wireless system to work.
Let’s look at an extremely simplistic definition of IMD. IMD is rogue or ghost signals that are created when using multiple wireless transmitters at the same time in close proximity to each other, or when transmitters are too close to receivers. These ghost signals can interfere with any receivers that are tuned to the same frequencies.
This is terrible news! How can we possibly use multiple wireless systems at the same time with all these rogue signals bouncing around the room? Not to worry! There are tools and techniques available to help you manage your installation. First, these rouge frequencies can be calculated based on the frequencies that you are using. There are many “Intermod Calculators” posted on the internet that allow you to enter the frequencies that you want to use and see what IM products will be created. These are very useful. Many, if not all, manufacturers of wireless microphone systems provide groups of frequencies that are compatible. Many wireless systems have the ability to scan for frequencies, keeping IMD in mind. There are commercially available applications that allow you to coordinate frequencies. Also, many manufactures provide applications that allow you to manage frequencies, such as Audio-Technica’s Wireless Manager.
Wireless Manager is a powerful, easy-to-use tool that allows users to create a device list, coordinate frequencies, and monitor Audio-Technica wireless equipment.
What Should You Do to Avoid or Minimize IMD?
First, coordinate your frequencies using one of the above tools. Second, put some space between transmitters and between transmitters and receivers. If you can operate your transmitters at a lower power, then do so. Seriously consider using an experienced integrator who has expertise with installing wireless microphone or IEM systems.
If you have further questions about this subject or any Audio-Technica product, please contact the Audio Solutions Department for additional assistance.