Is the Sky Falling on Wireless Mics?
By Jonathan Novick – Director of Sales & Marketing at Alteros
Originally published in TV Technology May 2019
Wireless mic systems that work today, may not work tomorrow and the day after may be different still. The days of set-and-forget are over, at least with traditional wireless systems.
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The UHF TV band available for wireless mics use in the US will be 34% smaller next year. The National Broadband Plan introduced in 2010 called for the auction of the 600 MHz TV band. The last date for TV stations to operate in that band is July 13, 2020. The changeover has already taken place in many markets, and in others, the transition is now in progress. Wireless mic systems that work today, may not work tomorrow and the day after may be different still. The days of set-and-forget are over, at least with traditional wireless systems.
All the changes and resulting spectrum crowding has put RF coordinators in high demand. The automatic channel selection features in high-end wireless mics can only do so much. The RF coordinator must carefully choose antenna type, placement, filtering, amplification and distribution to achieve high channel counts. Any small change to the external RF environment or the physical operating space may necessitate hours of additional system tweaking. This is causing the cost of operating traditional wireless microphones to rise significantly.
Without new spectrum for unlicensed wireless mics another solution was needed. The FCC allows license-free use of wide-bandwidth (high signal quality) devices in alternative frequency bands at very low power levels (below -41dBm). Traditional modulated carrier wireless mics (digital or analog) cannot operate within the data rate/bandwidth/power levels required for this alternative approach. However, using UWB as the basis of their GTX Series Local Area Wireless Mic Network (L.A.W.N.™), Alteros, Inc. has designed a highly-robust field-proven system that achieves top performance levels while meeting the FCC requirements.
UWB employs short pulses of RF energy instead of a modulated carrier. The pulse duty cycle is just over 1% which puts the average transmitted power well within FCC guidelines. But this isn’t the only benefit of UWB.
- UWB signals don’t generate intermodulation products
- Pulses are less prone to problems that impact modulated carriers.
- The transmitted data is never converted to the analog domain
The GTX Series operates at 6.5 GHz. The short wavelength doesn’t generally penetrate walls and other structures, (allowing high channel-use) and the signals reflect off surfaces creating a vibrant field of desired signals. What at first may be perceived as a challenge also offers some unique advantages.
One challenge at 6.5 GHz is that smaller wavelengths and antennas are more directional than lower frequencies. Reception is best via line-of-site between the transmitter and receiver. To create this condition, coverage and reception are enhanced by employing a mesh network of receivers (transceivers). Each GTX32 transceiver receives 24 mics simultaneously and 64 of them can be used at once. A single transceiver provides 100% signal quality when linked.
As with traditional wireless mic systems, diversity increases performance. Unlike traditional diversity, the GTX system can use up to 64 receivers in a single location (!) to create maximum diversity. Additional transceivers are used to extend the coverage area or split coverage into multiple independent zones. A master control unit then processes the signals using multiple techniques to insure flawless operation.
Another key advantage to low-power location-specific operation is that studios or buildings can deploy multiple GTX L.A.W.N. systems without interference between each other. Systems are each given independent IDs so that a transmitter can’t operate on the wrong system should it wind up in the wrong place.
The GTX System is truly digital. The pulse has two states; on and off. Signal phase and amplitude are not used as with modulated RF carriers. Up to 10,000’ of optical fiber can be used to directly connect transceivers without the need for analog RF to fiber conversions. Fewer conversions means fewer opportunities for problems/degradation. In fact, once a GTX transmitter converts the audio to digital, it remains digital all the way to the mixer. The result is pristine sound with low latency, low jitter and no dropouts.
The GTX Series supports up to 24 transmitters without requiring RF coordination between them. In other words, it delivers 24 channels with set-and-forget simplicity. The system gives RF coordinators 24 channels of breathing room for the other wireless systems to operate in. So maybe the sky isn’t falling on wireless mics after all.
Alteros Wins TV Technology Best Of NAB Show Award – GTX-FX8 Direct-To-Fiber System
April 2019 – Recipients honored for innovation, feature set, cost efficiency and performance. The awards are judged by a panel of industry experts on the criteria of innovation, feature set, cost efficiency and performance in serving the industry.