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Wireless Microphones & Frequencies

Wireless Microphones & Frequencies

mercoledì 10 maggio 2017 da Lizanne | Bax-shop

If you're thinking about investing in a wireless microphone or another wireless system, you'll quickly realise that there’s plenty to think about when it comes to picking out the right things. There’s also quite a bit of contradictory information online about how and where you can use certain wireless systems and frequency bands, but never fear, we're here to help!

This page includes all the information you need about how frequency bands work, where you can use them, and what kind of system is likely to meet the demands of your specific setup, so you can arm yourself with the right knowledge, make an informed decision and invest in a flexible system that can back you up for years.

Picking the Right Wireless Microphone

If you’re thinking about getting a wireless microphone system, we recommend having a read of our purpose-written Wireless Microphone Buyer’s Guide. It’ll give you all the info you need about the kind of microphones available, including handheld, headset and clip-on lavalier microphones, as well as how they can be hooked up to a system and the various frequency bands that systems use to receive and transmit. If you need some more in-depth info about wireless frequency bands, you’ll find it right here.

Microphones, Audio Signals & Radio Signals

Any normal microphone captures and converts sound into an electrical signal, which is then sent through a cable to a sound system. What a wireless microphone does is capture and convert audio into a radio signal that’s sent through the air via some form of transmitter so it can be picked up by a receiver. Since the receiver is connected to a sound system, this is where the sound that’s captured by the microphone is amplified.

The transmitter can either be integrated into the body of the microphone itself - like a handheld wireless microphone - or it can be an external unit worn as a beltpack that you can plug your headset microphone, clip-on microphone or even instrument into. All wireless systems include a receiver that’s hooked up to a sound system via a cable. The receiver converts the radio signal into an audio signal and feeds this to the sound system to be amplified.

Wireless in-ear systems work the other way around. Here, the transmitter is the part that’s plugged directly into the mixer or sound system, and the performer or musician has a beltpack receiver that picks up the radio signal sent out by the transmitter, and then feeds a connected set of in-ear headphones with audio.

Even though wireless systems solve the age-old problem of tangled, cumbersome cables littering the stage, it’s not 100% problem-free. Any wireless system sends and receives data via a specific radio frequency, and some frequencies are more prone to noise and even signal drop-outs caused by interfering radio signals or even phones and WiFi signals, and because you might be sharing the frequency with other systems, some can only be used when you have the right licence.

So, using random frequencies in the same space can cause problems because different systems will compete and interfere with each other. The UHF band, for example, is shared with telecom providers which use it for WiFi and digital TV, so it's really important to know which frequencies you're allowed to use and which ones may cause interference due to a large number of other users in the area.

Basically, you need to make absolutely sure that you’re getting a system that operates on the correct frequency band for your setup and location.

Intermodulation

Intermodulation is caused by the non-linear behaviour that happens when the signal of more than one wireless microphone system is being processed at the same time and at specific frequencies. In other words, it results in distorted sound - which no one wants.

So, if Signal 1 is transmitted at 824.1 MHz and Signal 2 is transmitted at 824.7 MHz, then intermodulation distortion (IMD) will occur both within and outside of these frequency bands because the frequencies are reacting to one another, causing small peaks and interference when they fall outside of their range. To prevent this, a margin needs to be maintained between the two frequencies. Multi-channel wireless systems often do this automatically, but the rule of thumb is: the more systems you use at the same time, the greater the margin needs to be. So, if you add a third microphone signal to the example above, then the margin would need to be twice as big. Another thing to bear in mind is that if you have a 16 channel wireless system, because of the ‘IMD effect’, it doesn’t mean you can use sixteen microphones at the same time.

Multi-Microphone Systems

The price and range of functions varies massively when it comes to the array of wireless microphone systems available these days. One of the most important points to think about when picking out the right system is how many additional microphones it can work with.

More budget systems usually operate on a fixed frequency so they can only handle one microphone, and while buying two of them and using them at the same time might seem like a good solution - it's actually not viable. More expensive systems can usually work with multiple frequencies so you can use multiple systems at the same time. The frequency band that a system operates on is usually included in the name of the system, so you can usually find what you need fairly easily. For example: the Sennheiser XSW 2-835 (E: 821-865). But it’s worth knowing that each brand has their own way of indicating the frequency.

Professional systems often come with handy software that can show you which frequencies are available in your area. Sennheiser offers the Wireless System Manager and Shure offers the Wireless Workbench. Sometimes, brands also offer free tools to help you find the frequencies available in your area, like Sennheiser's online FrequencyFinder tool and the Frequency Xpert app.

Frequencies: VHF & UHF

The most commonly-used radio frequencies that most wireless systems will operate on are roughly divided into two groups:

VHF (Very High Frequency): 30 MHz (30,000,000 Hz) to 300 MHz (300,000,000 Hz)
UHF (Ultra High Frequency): 300 MHz (300,000,000 Hz) to 3000 MHz (3000,000,000 Hz)

Most wireless microphones and monitor systems operate on the UHF band, which is split up into channels 21 to 70 (see figure 1). Each channel covers 8 MHz except the ISM band and the 1G8 bands. This distribution is used worldwide to indicate which frequencies you’re allowed to use per region.

In a lot of cases, you will need a licence to operate a wireless microphone system, but it’s easy enough to apply for a licence in the country where you'll be using the system. The rules vary greatly per country, so if you’re planning to go on tour, make sure the system you’re taking can be used in the region where you have your dates booked.

Licence-Free Frequencies

There are a number of frequency bands that can be used without a licence throughout Europe and even the world. For starters, there's something known as a band gap or Duplex Gap (822 - 830 MHz), which is basically a buffer between the uplink and download frequencies of mobile phone network providers. It's a really narrow gap, so it’s not suitable for using multiple systems at once. There’s also a higher risk of intermodulation-related distortion simply because wherever you are, there’s likely to be a lot of mobile phones in the area. This also goes for the 863 - 865 MHz band, which is just above the frequency range used by mobile phone providers, but the 822 - 832 MHz band can be used pretty much anywhere in Europe without a licence.

Systems that operate on the 2.4 GHz band (2400 - 2483.5 MHz) have a great advantage because they can be used anywhere in the world without a licence. Unfortunately, this also means it's a very popular frequency band, so it’s used for anything from microwaves to wireless signals like WiFi and Bluetooth. Many consumer appliances built in the last five years now operate on the 5 GHz band, which will hopefully create some room on the overcrowded 2.4 GHz band in the future. Another disadvantage of the 2.4 GHz band is that it has a very short wavelength, and the shorter the wavelength, the shorter the range, so you could probably only manage a range of up to 30 metres and would only be able to use six wireless microphones or in-ear systems at the same time as you’re using the 2.4 GHz band.

Continuous Development

Since mobile tech is always developing, the frequency-band landscape is constantly changing and making more and more room for wireless audio. In early 2016, the 800 MHz range was designated for mobile phone networks throughout Europe, so microphones that used to operate on the same frequency band no longer work. Now, the same thing is likely to happen for the 700 MHz band, since there are plans to block wireless microphones from using any frequency that lies between 694 and 790 MHz.

Licences in the United Kingdom

At home, in the UK, you can use the following frequencies without needing to get a licence:

863 - 865 MHz, max. 10 mW E.R.P.
173.8 - 175 MHz, max. 50 mW E.R.P.

There are two types of licences you can apply for in the UK via the OFCOM website.

With a Standard Licence, you’re requesting permission to use a fixed frequency in a fixed location at a fixed time. The advantage of this is that OFCOM coordinates the frequency band in such a way that users don’t interfere with one another. The frequency bands available for this type of licence are 470 - 790 MHz and 1780 - 1800 MHz.

With a UK Wireless Microphone Licence, you get permission to use a frequency band for 1 or 2 years. Once you have your licence, you can use this frequency band anywhere in the United Kingdom. The use of these bands is not coordinated by OFCOM, so some interference from other users may occur. Unlike a Standard Licence, you’re allowed to switch to another frequency with the UK Wireless Microphone Licence. The available frequency bands for this type of licence are UHF channel 38 (606 - 614 MHz) and VHF (175.250 - 209.800 MHz).

Licences for The Netherlands

If you're on tour in The Netherlands, you can use the following frequencies without needing to get a licence:

195 - 202 MHz, max. 50 mW E.R.P.
470 - 604 MHz, max. 50 mW E.R.P.
614 - 694 MHz, max. 50 mW E.R.P.
823 - 826 MHz, max. 20 mW E.I.R.P. (for handheld), 100 mW E.I.R.P. (for beltpack)
826 - 832 MHz, max. 100 mW E.I.R.P.
863 - 865 MHz, max. 10 mW E.R.P.
1785 - 1805 MHz, max. 20 mW E.I.R.P. (handheld), 100 mW E.I.R.P. (beltpack)

The 470 - 694 MHz band isn't available everywhere in the Netherlands because it’s shared with the digital broadcasting network. Broadcasting network frequency usage differs depending on the region. This means the availability of frequencies for wireless microphones is also different depending on the region. If you want to know which frequencies can be used in any specific location in the Netherlands, use the Microfoonbanden app provided by the Agentschap Telecom (the Dutch Telecom Agency).

Licences for Belgium

If you're on tour in Belgium:

As well as the 822-830 MHz, 863-865 MHz and 2.4 GHz bands, the 518-526 MHz and 534-542 MHz bands can be used without the need for a licence in Belgium. The 606-614 MHz band is reserved for scientific radio astronomy. All other frequencies require a licence. You can request a licence via the Belgian Institute for Postal Services and Telecommunication. You can also download a complete list of available frequencies per region.

Licences for France

If you're on tour in France, you can use wireless microphones and in-ear systems on the following frequency bands:

174 - 223 MHz, max. 50 mW E.R.P.
470 - 694 MHz, max. 50 mW E.R.P.
823 - 826 MHz, max. 20 mW E.I.R.P.
826 - 832 MHz, max. 100 mW E.I.R.P.

As long as you’re not exceeding the maximum output, you don’t need a licence to use the frequencies listed above. If you need more output for larger-scale events, for example, then you can apply for a licence from the French government ARCEP (Audio Programming and Special Events), which is valid for up to two months.

Licences for Germany

If you're on tour in Germany, you can use the following frequencies without needing to get a licence:

174 - 230 MHz, 50 mW E.R.P.
823 - 832 MHz, 100 mW E.I.R.P.
863 - 865 MHz, 10 mW E.R.P.
1785 - 1805 MHz, 82 mW E.I.R.P.
1795 - 1800 MHz, 20 mW E.R.P.

You will need a licence to use the 470 - 694 MHz band, which you can apply for by downloading a form at the official Bundesnetzagentur website (Regulatory Authority for Telecommunications and Post). The licence is valid for a specific location for up to 30 days.

Licences for Sweden

If you're on tour in Sweden, you can use the following frequencies without a needing to get licence:

823 - 826 MHz, max. 10 mW E.R.P. (handheld), 50 mW E.R.P. (beltpack)
826 - 832 MHz, max. 50mW E.R.P.
863 - 865 MHz, max. 10mW E.R.P.

For the frequency bands below, you'll need to apply for a licence from the Swedish Government: PTS.

174 - 240 MHz, max. 50 mW E.R.P.
470 - 694 MHz, max. 50 mW E.R.P.
1785 - 1800 MHz, max. 20 mW E.R.P. (handheld), 50 mW E.R.P. (beltpack)

Licences for Spain

If you're on tour in Spain, you only need a licence if you plan to exceed the maximum E.R.P. output level. You can apply for a licence via the Spanish Government website. The maximum output levels per frequency are listed below:

174.100 - 179.300 MHz, max. 50 mW E.R.P.
188.100 - 194.500 MHz, max. 50 mW E.R.P.
470 - 786 MHz, max. 50 mW E.R.P.
823 - 832 MHz, max, 20mW E.I.R.P. (handheld), 100mW E.I.R.P. (beltpack)
863 - 865 MHz, max. 10mW E.R.P.
1785 - 1805 MHz, max. 20mW E.I.R.P. (handheld), 50 mW E.I.R.P. (beltpack)

Licences for Italy

If you're on tour in Italy, you only need a licence if you plan to exceed the maximum R.R.P. output level. You can apply for a licence via the Italian Government website. The maximum output levels per frequency are listed below:

823 - 832 MHz, max. 10 mW E.R.P.
863 - 865 MHz, max. 10 mW E.R.P.
174 - 230 MHz, max. 50 mW E.R.P.
470 - 786 MHz, max. 50 mW E.R.P.
786 - 790 MHz, max. 12 mW E.R.P.
1785 - 1805 MHz, max. 20 mW E.I.R.P. (handheld), max. 50 mW E.I.R.P. (beltpack)

Border Regions

The regulations regarding the use of wireless microphone frequencies in border regions is more unique. Basically, you’ll need to follow the rules and regulations of the country you’re physically in. This doesn’t mean that you definitely won’t experience interference and IMD from users on the other side of the border. Even if someone is using the same frequency as you with exactly the same system, chances are your continuous signal will be stronger and more stable than the 'rival' signal, which should keep IMD-related distortion to a minimum.

Wrap-Up

While you should be fully kitted out with the knowledge you need to make the right decision when you pick out your wireless system, the one you finally go for will still depend on a few important points. One of the biggest points is the problems thrown up when multiple users are on the same frequency band at the same time. At large-scale events where multiple systems are sending signals all over the place, allocating the available frequencies is absolutely essential, so make sure you have the licence you need so you can avoid any nasty surprises!

If you need help with your wireless setup and how you’re planning to use it, feel free to send us an email or give us a call and one of our specialists will be happy to offer some expert advice.

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