Wireless microphones - TvTechnology

Wireless microphones

When the analog switchover is complete, it is likely to cost a lot more to operate wirelessly.
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Wireless microphones have freed interviewers from the hazards of trailing cables. Shown here is an XDCAM camcorder fitted with a Sony WRT-807B wireless microphone receiver.

Since wireless microphones were introduced many years ago, they have increasingly been used within the broadcast industry. In the early days, wireless mics were primitive beasts with the sole purpose of replacing a piece of 600Ω cable. This, as many know, is not as simple as it sounds. Over the years, many users have experienced issues with a wireless microphone system, including intermodulation, outside interference, and associated pops and splats.

Despite the foibles of wireless mics, the industry has in some ways become dependent on them. Many program makers would be hard-pressed without their presence, not only in the studio but also in the field. Wireless mics provide freedom to the users as well as the program makers. Much of today's TV content would be almost impossible to make without them.

Over the years, manufacturers have used technology to make these devices easier to understand, easier to set up and easier to use. That, in turn, has created even more reliance for program makers. Years ago, you would not have dreamed of using a wireless microphone on a presenter who did not move; he or she would have been firmly tethered to a patch box somewhere on a studio wall.

Now in the fast moving world of program making, even the presenter who sits behind a desk and doesn't move around is equipped with a wireless microphone. Why? Because it is easier to handle and use a wireless microphone than it is a cable. As program makers have become more and more adventurous in their exploits, the demand for wireless microphones has increased. The climate is changing, and what is happening now may foretell other changes in the use of wireless microphones.

Analog switch-off

Wireless microphones are normally used within what is referred to as the white space, or unused spectrum, between TV channels. Broadcasters also use channels in this white space for in-ear monitors and other RF devices associated with program making.

Often this is used for fixed site applications, as the white space that is used is geographically interleaved and can only be used in certain areas. For example, in the UK, there is also reserved spectrum at channel 69 (854MHz to 862MHz), which is more commonly used by roving wireless microphone users because it is available countrywide.

As analog transmitters are switched off, the channels that are normally used for the above purpose will undoubtedly be sold off. This is commonly known as the digital dividend, as a single digital equivalent of one analog channel occupies less spectrum than its analog counterpart. Respective governments and regulatory bodies have looked into this issue and decided that there are not many wireless mic users. Therefore, they think there is revenue to be gained from licenses for wireless mics.

From this data, it would seem that the channels dedicated to wireless mics were underused. This is a problem in its own right because many wireless mic users never purchase the necessary licenses. The most likely next step will be a spectrum auction. Some companies in the telecommunications industry are straining at the leash to get their hands on this spectrum.

Mobile TV demands

An auction would provide these companies the spectrum they require to offer, among other things, mobile TV. In the United States, this scenario is already being played out, and sections of spectrum have been sold off for tens of millions of dollars. I recently spent some time with a broadcaster in Sweden and saw its proposed spectrum availability. I could see immediately that this was going to cause the company problems. It is not too much of an issue for fixed sites such as studios because they will be able to get licenses to operate their wireless mics.

Changing frequencies

There may be an issue of how many frequencies can be used. However, the frequencies that RF microwave users are currently employing are set to change. This means that current equipment will be rendered useless. Some equipment could be modified to operate within the new channel allocations, but this can be about as expensive as buying new. So the changes to the spectrum will undoubtedly mean that users will have to invest in new wireless microphones. In addition, the reallocation of spectrum will cause problems for the ENG crew. Because the allocation of spectrum is regional, roving news crews may need several wireless microphone kits, depending on where they are reporting.

Also, because no one frequency band is allocated for this purpose, no single wireless mic can cover all the frequencies required. Again, this will require investment in new equipment. The alternative is that this particular area of broadcasting will simply go back to using a wire. This issue will not only affect the broadcast industry, but also the entertainment industry. If there are not enough channels allocated even on a regional basis, then theater shows will suffer. The modern theater shows regularly use 24 to 36 or even more channels of wireless. The problem will also hit touring bands because they will need a multitude of wireless systems to just move the show around a single country. Then there are the truly huge events such as the London Olympics in 2012. If current plans are executed, then much of what is planned for Olympic TV coverage will be rendered impractical.

There also seems to be little common regulation between countries because each country has its own ideas and plans for the newly available spectrum. There has been much talk of unified bands that cover Europe, as this would make things far easier for all concerned. We currently have a unified band in 1785MHz to 1800MHz, but as of now no manufacturers have taken up this band. This is probably because manufacturers do not see this band as a real solution. One issue is that the band is quite narrow and would only realistically permit the use of about 18 wireless channels. There is talk of using other bands, but these still do not seem to be the answer.

Digital technology

One possible solution would be to use digital wireless microphone systems. Digital wireless can offer more channels of wireless within a given amount of spectrum. It is also easier to change frequencies with a digital system. In addition, the lower down the spectrum you go, the larger the RF parts get. This means that manufacturers have to redesign printed circuit boards and, in some cases, create entirely different models to operate in the lower bands.

Digital processing makes the entire process easier because it does not require the total board redesign to change frequencies. Digital wireless mics can easily have interchangeable modules that permit rapid frequency change, and this can often be an important operational advantage.

Future choices

Wireless systems will continue to be used, but there are going to be some stark choices for program makers, touring bands and theaters alike. If there is insufficient spectrum available or the right technology, will these applications be happy to go back to using long lengths of 600Ω cable? With the opportunity for governments to make large sums of money through auctions, user needs may get left behind.

When the switchover is complete, the new spectrum plans are allocated and the auctions have been held, it is likely to cost a lot more to operate wirelessly than it does today. That could make the price of microphone cable look attractive.

Some countries are further advanced in this area than others. Over the next couple of years, it is going to be interesting to see just how this saga plays out. Most countries have their own regulatory bodies and lobby groups. You may want to contact them or your current wireless microphone supplier to find out more. For the EU region, see the Association of Professional Wireless Production Technologies (www.apwpt.org) and the Radio Spectrum Policy Group (rspg.groups.eu.int).

Simon Beesley is European product manager at Sony Europe.