THURSDAY, AUGUST 23; Frequency Coordination for Wireless Systems
Learn (or brush up on) the basics of frequency coordination for wireless microphone systems, including practice scenarios utilizing the frequency compatibility function of Shure Wireless Workbench® software.

Times
10:00 AM – 11:00 AM CDT  Register for the 10 AM webinar
2:00 PM – 3:00 PM CDT  Register for the 2 PM webinar

TUESDAY, AUGUST 28; Axient® Wireless Management Network Overview
Discover all the new the features that Axient® brings to professional wireless microphone users.

Times
10:00 AM – 11:00 AM CDT  Register for the 10 AM webinar
2:00 PM – 3:00 PM CDT  Register for the 2 PM webinar

After you register, you’ll get a confirmation email that’ll tell you how to join the webinar.

System requirements for PC-based attendees: Windows® 7, Vista, XP, or 2003 Server. For Macintosh®-based attendees: Mac OS® X 10.5 or newer required.

Happy learning!

View archives of our webinars at your convenience on shure.com.

Fixed device Agility White Space Radio currently being tested in Wilmington, North Carolina

Deployment of the KTS device will initially be limited to the Wilmington, NC area and will eventually expand nationwide.

Users of wireless audio systems have been aware of the potential threat created by these TV band devices for many years, since the FCC began to investigate using the ‘white spaces’ vacated by analog television in the UHF and VHF TV bands to provide wireless broadband Internet access.  On June 12, 2009, the Digital Television (DTV) Transition was completed and analog television broadcasts by major stations ceased by FCC mandate. After years of regulatory planning, debate, and product testing, the future is here.

How it affects consumers

TV band devices (eventually there will be both fixed and portable models) will operate alongside wireless microphones used by broadcasters, theatrical producers, sports franchises, music tours and other productions.  Their goal will be to expand reliable wireless broadband internet coverage to underserved rural areas and dense urban populations, improve internet access for schools and public buildings, provide new data management systems for corporations, and create networks in homes. Although there are numerous technical challenges to sharing the TV spectrum frequencies, the benefits to the American public are significant.  Due to their ability to penetrate obstacles and reach longer distances than higher-frequency Wi-Fi, some have described WSDs as a game-changer that will positively affect all of us.

Here’s what FCC Chair Julius Genachowski had to say: “With today’s approval of the first TV white spaces database and device, we are taking an important step towards enabling a new wave of wireless innovation. Unleashing white spaces spectrum has the potential to exceed even the many billions of dollars in economic benefit from Wi-Fi, the last significant release of unlicensed spectrum, and drive private investment and job creation.”

How it affects wireless audio users

A TV Bands Device can only transmit on TV channels that it knows are unassigned to a TV station or other licensed user.  The device receives this information from one of 10 FCC-approved TV Bands Device Databases. The first database, operated by Spectrum Bridge Inc., also went live on January 26.

As these new devices begin sharing the same TV channels used by wireless microphones, personal monitors, and production intercoms, interference will become a real possibility.  Fortunately, the FCC has set aside a minimum of two TV channels in each market that are available exclusively for wireless audio systems.  These are off-limits to TV Bands Devices.

Since 3-15 wireless microphones (depending on model) can operate in one TV channel, the reserved TV channels will accommodate the needs of most wireless users.  Users of larger numbers of wireless systems may register in the TV Bands Device Database to protect additional TV channels during a specific event.  Unlicensed wireless microphone users must request database protection in advance from the FCC, while licensed users may register in the database directly.

Here’s what wireless users need to do to insure continued trouble-free operation of their gear:

1. Take inventory
Make a list of all of your wireless mics, in-ear monitors, and intercoms that operate in the VHF or UHF TV bands (174-216 MHz and 470-698 MHz, respectively.)  You’re looking for the “3 M’s” (Make, Model, and MHz).  Note the exact frequency that each product is actually set to as well as the frequency range that it is capable of transmitting on.  This is important because it tells you what your options are if changing frequencies becomes advantageous.

2. Do some research  

Find out which TV channels are exclusively available for wireless mics at your venue’s location.  You can easily check this online, using Spectrum Bridge’s online Show My White Space tool.

(http://whitespaces.spectrumbridge.com/whitespaces/Home.aspx).

3. Compare
You’re free to operate on any TV channel that isn’t assigned to a TV station or licensed two-way radio user. Ideally, you’d want all of your wireless gear to be set to frequencies in the TV channels that are reserved for wireless audio systems at your location.  If they’re not, you may want to keep that in mind when planning for future equipment upgrades.

4. Start planning  
If you need more wireless systems than will fit into the reserved TV channels from time to time, you’ll want to register in the database at least 30 days before the event to protect them from interference.  Now is the time to think about that music festival, convention, or Christmas concert.  It’s a good idea to start planning for these special events sooner rather than later.  If you’ll be supplementing your facility’s own wireless systems with additional rented gear, find out in advance which TV channels you want to use.  Do your preferred rental providers have those frequency ranges in stock?  Making phone calls now will avoid nasty surprises two days before an important event.

 Still, it doesn’t have to be guessing game.  Understanding the basics of how wireless systems and radio waves function will help you consistently triumph over dropouts, interference and distortion.  You can start right now by avoiding these common errors.

 1. Signal blockage

Maintain line-of-sight between the transmitter and receiver antennas as much as possible. Avoid metal objects, walls, and large numbers of people between the receiving antenna and its associated transmitter.  Ideally, this means that receiving antennas should be in the same room as the transmitters and elevated above the audience or other obstructions.

The human body can also interfere with wireless signals. Largely composed of water, our bodies absorb RF energy. In addition, if a user cups his or her hands around the external antenna on a handheld transmitter, its effective output can be reduced by 50 percent or more. Similarly, if the flexible antenna on a bodypack transmitter is coiled or folded, the signal suffers.

 2. Incorrect antenna type or placement

Receiver antennas are one of the most misunderstood areas of wireless microphone operation. Mistakes in antenna selection, placement, or cabling can cause short range, dead spots in the performance area or low signal strength at the receiver that leads to frequent dropouts. Modern diversity receivers offer much better performance than single-antenna types, but the right antennas must still be put in the right place to maximize the performance and reliability of the system.

To ensure good diversity performance, space antennas apart by at least one-quarter of a wavelength (about 5 inches at 600 MHz). The receiver antennas should be angled apart in a wide “V” configuration, which provides better pickup when the transmitter is moving around and being held at different angles.
Try to keep antennas as close to transmitters with line of sight as is possible. Antennas can also be frequency band-specific. Don’t try to use an antenna from another system without double-checking the frequencies first.

If the receiver will be located away from the performance area (in an equipment closet or a closed rack, for example), ½-wave antennas or directional antennas should be remotely mounted (ideally above the audience) in order to have a clear line of sight to the transmitters. (Short ¼-wave antennas should never be remotely mounted, however, because they use the receiver chassis as a ground plane.) Increasing the separation between diversity antennas up to one wavelength (about 20 inches at 600 MHz) will improve diversity performance.  Beyond one wavelength, extra distance between the antennas will not significantly improve diversity performance, but may allow better coverage of a large stage, church, or meeting room.

If the antennas will be far from the stage, use directional antennas to improve reception by picking up more signal from that direction and less from other angles.

If the antennas will be connected to the receiver with a length of coaxial cable, in-line antenna amplifiers may be required to overcome the inherent signal loss in the cable. The amount of loss depends on the exact length and type of cable used, so follow the manufacturer’s recommendations.  Total net loss should not exceed 5 dB.

3. Poorly coordinated frequency set

A properly coordinated set of wireless frequencies must satisfy two criteria:

• Frequencies must avoid local active TV channels
• Frequencies must be mutually compatible

 Television transmitters may operate at power levels up to one million watts while wireless microphone systems typically have only 50 mW (fifty one thousandths of one watt!) or less  output power.  To combat broadcast television interference, avoid using frequencies of local active TV channels.

How local is local? “Local” is generally considered to be up to 50 or 60 miles, depending on the coverage area of the particular TV transmitter and on the location of the wireless microphone system. The good news is that indoor setups are at less risk than outdoor setups because building structures will usually strongly attenuate TV signals. Inside buildings of substantial construction, it may be possible to ignore TV stations as close as 30-40 miles. Still, since the locations and assignments of television stations are well known, it’s pretty easy to choose relatively safe wireless microphone system frequencies in a particular area.

To insure a mutually compatible set of frequencies once the local TV channels have been taken into account, it is necessary to use one of two methods.  The simpler method is to use the “Group” and “Channel” frequencies that are already programmed into the wireless systems.  By using Channels that are all in the same Group, compatibility is guaranteed for small setups of like equipment.  The appropriate Group and Channels can be determined from a link to the manufacturer’s website or often by using the built-in “Scan” function on the receiver itself.

If the wireless setup is more complex, for example using wireless microphones and wireless in-ear monitors together, it may be necessary to use a frequency coordination computer program to insure compatibility.  Wireless manufacturers can assist in these situations.

 One frequency does not fit all. If you are touring, one consequence of the newly dense TV channel distribution in the US is that it is not generally possible to use a given set of wireless microphone frequencies everywhere in the country.

There is no such thing as “set and forget”.

Even if your audio system doesn’t move from place to place, the radio environment can change unexpectedly. It’s largely true that television stations remain constant, but if there are other wireless systems in the frequency band – whether it’s multiple systems in your own location or interference from the coffeehouse down the street – your wireless frequencies may need to be adjusted. What worked at sound check may not be failsafe when the show begins. And that’s why frequency coordination is so important.

 4. Poor battery management

Despite the fact that transmitter battery life is a top concern with wireless mics, users continue to try and cut operating costs by using inexpensive batteries. Most wireless manufacturers specify alkaline or lithium single-use batteries because their output voltage is very stable over the life of the battery. This is important because most transmitters will exhibit audible distortion or signal dropouts when supplied with low voltage. Rechargeable batteries often seem like the ideal solution, but many rechargeables provide about 20 percent less voltage than a single-use battery — even when they are fully charged.

 To combat battery problems, carefully compare the transmitter’s voltage requirements with the battery’s output voltage over time to make sure that the battery will last through a full performance. For 9-volt applications, there are lithium-ion types that work well, while Ni-Mh and Ni-Cad batteries may last only a couple of hours. For AA applications, Ni-Mh rechargeables offer similar performance to single-use alkaline batteries.

Using rechargeable batteries is a great way to save money and landfills as long as you or someone on your staff is able to effectively manage them. Remove batteries from transmitters after each performance. This will keep you from using half-dead batteries the next time you need them and will also prevent an accidental leak from damaging your transmitter if stored for an extended period of time.

 5. Improper gain set-up

Setting the proper input gain is one of the most important adjustments on a wireless microphone system. Distortion may occur if the gain is set too high, while poor signal-to-noise may result if the gain is set too low.

Most wireless systems have a gain control on the transmitter itself in the form of a switch, a pot, or a programmable adjustment.  It may help to think of this gain control as serving the same function as the “trim” or “gain” adjustment on a mixer.  Its purpose is to set the input sensitivity low enough to prevent input overload or “clipping” but high enough so that the signal level is well above the system noise floor.

Adjustment of the wireless transmitter gain is done in the same way as mixer input gain:  set the gain control so that the loudest input signal just barely lights the overload or peak indicator.  For a wireless system this indicator is usually on the receiver, so it is necessary to observe the receiver front panel while the performer is singing or playing.  If the peak indicator is flashing constantly, reduce the transmitter gain until it flashes only occasionally.  If the indicator never flashes, increase the gain until it flashes just on the loudest signals.

Many wireless microphone systems have an output level control on the receiver.  Since this control only affects the receiver output, it has no effect on improper gain adjustment in the transmitter.  That is, if distortion or poor signal-to-noise is occurring in the transmitter, it cannot be “fixed” by changing the receiver output level.  Most professionals recommend leaving this control at maximum.  As long as the mixer input can accommodate this level, the overall system will exhibit the best possible dynamic range.