Recommendations for the use of RF

In this article the reader will be able to analyze some technologies that are available in the market. It is not a criticism of systems or brands, it is an objective evaluation of the solution, so that each user or technician can make a decision.

Juan Tamayo

In recent years the professional audio industry has taken audio streaming into wireless networks seriously. And is that not having cables on the stage improves and facilitates the operation of any event, but are we sure of this? We see how different manufacturers have launched new technologies and elements that improve quality, although some doubts arise at what cost? What are the implications of having wireless networks? What are the implications of using new technologies?

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Before starting with the evaluation, let's start with the user, when to have a wireless system? Wireless systems are used when there is mobility, when the person needs to travel across the surface without danger to the cables being entangled. This means that if you are going to leave the microphone on a static basis, and the person will not be moving, avoid using wireless systems, as it will have a higher production expense and can significantly increase RF problems.

Remember that when you have 2 or more wireless microphones, they generate an interference called intermodulation, and basically they are frequencies that appear by the ratio in the RF spectrum. I will not delve into the subject, but this is solved with the protocols and management software of the manufacturers. Let's not forget that every time the RF spectrum is narrower, since digital channels and cellular telephony are occupying them.

In the United States, the FCC has just banned the 600 MHz band. So now there is less operating space but everyone wants more RF channels. The RF spectrum is not renewable, once full there is no way to expand it.

Analog or Digital
The industry has not decided which is the best model of transmission, send analog waves, or data frame in digital format. I think it depends a lot on what you want the production, but I make some recommendations.

No matter what format you send in, first check the frequency range. It is useless to have a digital system if it is in a band saturated with RF information. If you already decided on which band you want to broadcast, let's look at the options that the two models give us.

In the analog one is usually used a carrier wave and accompanied to this wave, on the same distance, two frequencies are sent. For example, if the carrier is in the 600 MHz, the information is sent in 599.5 MHz and 600.5 MHz (example mode) and the receiver receives these 3 frequencies. With the accompanying frequencies it analyzes if the transmission is waiting and receives secondary information such as battery status, name, among others. Then, if the system is analog, it will have a higher or higher number of frequencies.

Now, if the system is digital, it usually receives only the carrier wave, since in the data bit frame (ones and zeroes) the transmitter identification is found, it does not require accompanying frequencies. It is also more protected to the signal-to-noise ratio than analog systems. An analog system requires 30 dB above the noise to be heard well, digital systems only need to be above 20 dB (10 dB is much the difference).

But perhaps the most notable difference is that digital systems do not have a filter called "compender", which "compresses analog transmission" to optimize the communication resource. As it sends a data frame, digital systems generally transmit between 20 and 20 KHz, while analogue ones reduce this acoustic bandwidth considerably.

One problem with digital systems is that they have a higher latency than analog systems, sometimes it is not dramatic. Well, it's usually not dramatic, but in some labors it can be, like in measurement, control, checking.

What to take into account when acquiring digital transmission?
It is the responsibility of the manufacturer and the user to know the pros and cons of any system to be acquired. In the digital transmission there are small letters that must be studied judiciously.

Using high channel density means that digital systems could increase channel density. But very careful, to achieve this you have to make sacrifices, and the first is to reduce the power of the transmitters. Reducing power reduces the range (distance) and avoid obstacles.

Better control of the system: with digital systems there is the possibility of better control, in some systems this is done automatically using two transmission frequencies, in other systems must acquire the control antennas separately and have the appropriate transmitters . How profitable is it to locate more networks?

Different frequencies outside the commercial spectrum: digital systems allow to transmit in very high frequencies, some do in the 1.9 GHz, others in the 2.4 GHz and even reach the 6.5 GHz, for this one has to have the following recommendations: the greater The frequency, possibly the range of distance decreases and the possibility of avoiding obstacles is less.

If you use the range of the 2.4 GHz is occupying the same space as the Wi-Fi transmission and Bluetooth. The ideal is to use automatic control systems. My recommendation is to try to get out of commercial UHF bands to avoid inconveniences in the future. Although with wide spectrum systems gives us the possibility to search for clean frequencies more easily.

Wireless systems deserve attention. Ideally, each company should be responsible for the RF networks, and monitored with the different technological aids offered by the market. Every day new technical articles, tools, training. Make use of these resources and you will be responsible for your RF spectrum.

Remember that you can use my contact information jtamayo@atus.com to resolve any doubts or concerns you may have. I hope this column is beneficial for the development of live events or installation.

Quoting products and technical services for Latin America

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