As anticipated, the current one-year 600 MHz spectrum transition period is indeed presenting a greater challenge to wireless (microphone, in-ear monitor and intercom) system operators in the United States than any event in the history of man-made radio on planet earth.
The spectrum-auction dust has settled in most cities and T-Mobile has energized in more than 10,000 counties across the nation — making some 30 percent of wireless systems illegal to operate.
Consider the use of any system over 608 MHz to be a distant memory, except for the two guard bands of 614-616 and 652-663 MHz. Most event producers and coordinators are oblivious to this fact, and continue to specify an increase in the number of wireless systems for their productions. And we, the RF techs, keep coming through with successful results, which only serves to further feed fuel to the fire of “more wireless.”
At this point, we’re operating in approximately 6 percent of the traditional UHF radio spectrum in comparison to what was available in 1962. Yet, there’s a silver lining to this cloud. Fortunately, wireless audio devices have evolved alongside the radio congestion being caused by the spectrum auction and TV repack.
Further, the 614-616 MHz and 652-663 MHz guard bands are extremely useful because, at least currently, they’re quite clean and quiet. I use both regularly on large events with tremendous success.
In addition to all of that, wireless manufacturers have introduced systems in the 941-960 MHz band that was recently opened up by the Federal Communications Commission (FCC). This, coupled with the fact that the frequencies of digital wireless systems can be packed much closer together, is assisting in our plight. Digital transmitters have more linear RF amps, which results in reduced intermod distortion and thus allows the use of more systems in a smaller radio spectrum. Amplitude modulation and a resurgence of the VHF spectrum are also providing some relief.
But, at this point, consider it illegal to operate any wireless audio device between 616 and 652 MHz. However, don’t throw out your equipment above 608 MHz – certain popular brands of systems may still operate in the guard bands. Analog systems also have their place with some interesting advantages over digital.
Due to all of the frequency congestion, we must employ every trick available to increase our chances for success. This includes implementing a radio spectrum band plan. Before every event, determine the expectations of the person in charge. Place RF IFB (interrupt foldback) systems in one band, wireless intercoms in another, wireless IEMs in a third band, and finally, wireless microphones in a fourth.
By implementing a band plan, we lower the RF noise floor around every system, resulting in greater range, better audio quality, and a more robust signal. Additionally, do your homework with respect to antennas. At this point, I recommend the use of multi-polarized antennas such as helical and CP (circularly-polarized) designs. At a bare minimum, directional paddles should be deployed. They provide the transmitter with a 15-30 dB advantage over any interference considering the forward gain and front-to-back ratio rejection of directional antennas.
We’re not completely out of the woods yet, though. There are still a few areas in the country yet to complete the TV repack, and many low-power TV stations haven’t yet moved. Let’s pull out our toolbox of tricks again. For example: by now, everyone working with RF should be using some type of radio spectrum monitoring equipment. It can be a software program that connects to wireless systems or a more sophisticated spectrum analyzer.
The bottom line is that we can’t see RF without these tools, and we must. It’s also highly advised to employ some type of wireless intermod (intermodulation) analysis software.
We must be educated in every aspect of this craft. With the power of knowledge, it’s far more likely to be successful regardless of event size. Recently, I completed a large-scale show with well over 100 wireless devices held in a post-TV repack city where T-Mobile has firmly established its roots. And now that it worked, I’m sure that the producers will add even more wireless for next year.