Issue link: https://digital.copcomm.com/i/1530210
Winter 2025 – LOCAL695.COM 29 Everyone who has coordinated wireless microphone systems is familiar with intermodulation or intermod. All wireless microphone systems, whether they are analog or digital, create intermodulation. Digital microphone systems have extremely linear components in addition to transmitting at lower power outputs. Thus intermod is kept to a minimum. Intermod created by digital wireless microphone systems is typically below the noise floor. WMAS systems allow engineers to stack the transmitted signals in a system with improved emission masking and filtering, and place the intermod on the ends of the wideband carrier. Intermodulation is therefore not a factor to the end user of a WMAS system. All these benefits sound excellent, so let's explore some of the limitations to a WMAS system and explore why a user still might consider using a narrowband system. Due to the wideband carrier of WMAS, you will need to have a fairly clean area of spectrum to place your wideband carrier. It could require a carrier up to 6MHz wide. This may be challenging based on location and spectrum availability. You can't place this carrier, for example, in the very small sections between digital TV stations or, if needing a full 6MHz, in the guard band. A full 6MHz wide system will be difficult to deploy in most major markets in the U.S. unless using it in the duplex gap or in the STL band or having the ability to use smaller wideband carriers. Another limitation to WMAS is the redundancy factor. These devices will typically be built with high channel counts into one physical box. Certain things like power and the audio interface are easy to make redundant, but if the entire box went down, it would affect all of your wireless channels. Users will need to ask themselves, "How many eggs should I put in one basket?" Manufacturers will need to develop extremely robust systems, as well as offer redundancy in their ecosystems, especially for mission critical applications. An area of WMAS systems that could both be a benefit as well as a limitation is the lower RF power. Lower RF power is beneficial because it allows more systems to be physically closer together utilizing the same TV channel than a higher power system, but it probably won't be able to have the reach that a higher power narrowband system could offer. If your circumstance requires a longer distance transmission, then a narrowband system may still offer a greater benefit than a WMAS system. One area of development that I believe to be important is how the system deals with RF interference. If you experience interference on a narrowband system, it would typically only affect one or two channels at a time. A WMAS system has all channels sharing a single RF carrier, so the concern for interference is much greater. A potential user of WMAS will need to understand how each manufacturer's system deals with interference. The need for a system to be able to deal with RF interference will be an important factor in the use of a WMAS system. How many interference events a system can take, how it heals itself, and how resilient is it to RF noise will all be important factors in a WMAS deployment. Manufacturers have already started to design, test, market, and release WMAS systems. Each system will have its own design, specifications, and features. Unlike Wi-Fi products that are all compatible with each other, WMAS systems will likely not be compatible across manufacturers. Each manufacturer will have their own proprietary system based on their interpretation of WMAS and based on their own codecs and algorithms. Shure recently announced their first WMAS product, the Axient Digital PSM, will available in January 2025. I've had the opportunity to explore what the WMAS deployment entails in this new product and it's very exciting. Axient Digital PSM is a single-space rack mount digital IEM system that has both four stereo narrowband carriers, as well as four WMAS wideband carriers in the unit. Each of the four WMAS carriers is 800KHz wide with four stereo channels in each carrier. This allows the unit to have up to sixteen individual stereo IEM mixes in one RU. In combination with an AD600 spectrum manager and AD610 Showlink access point, the unit will be able to manage frequency deployment and interference events. Within each 800KHz carrier are four 200KHz wide subcarriers. If an individual subcarrier experiences interference, the other three subcarriers will not be affected by that interference. For more information, you can visit Shure's website. There is still a lot to learn about WMAS. It offers so many possibilities for the future of RF systems and will only continue to develop as technology advances. Each manufacturer will have their own approach, but that will just provide more tools in the toolbox to choose from. We live in challenging times for wireless microphone systems but one thing that this framework encourages is that we should all be good RF neighbors. "A major advantage is the ability to deploy a high channel count. Large events such as major sporting events, large conventions, live theater, and reality TV—which all typically need hundreds and hundreds of wireless channels—will benefit greatly from the increased spectral efficiency that WMAS offers."