Which RF Band is Right for Your Wireless Dimming Requirements? An Interview

Sharon RC4

Aug 8, 2017
An Interview with James David Smith, Chief Product Developer at RC4 Wireless, Has Some Answers.

What frequency do most wireless DMX systems use?

JDS: Almost all commercial wireless DMX systems operate in the 2.4GHz band, which is harmonized worldwide. Although the generic range of this band is from 2.400GHz to 2.5GHz, the more constrained truly international range is 2.412 t0 2.472GHz. A handful of Wireless DMX systems will operate in the 5.8Mhz band, from 5.725GHz to 5.875GHz.

How do you know which RF band is right for your project?

Deciding which RF band is right for any given project is relatively easy when a handful of simple technical facts are taken into consideration. All else being equal (RF power, antenna gain, etc.) lower frequencies propagate better than higher frequencies. Thus, range is better, and signals pass through objects more readily at lower frequencies. In just about every humanly perceivable way, lower frequencies work better.

Basically, there are three wireless bands: 2.4GHZ, 5.8GHz and 900MHz. Each has unique advantages and disadvantages.

What’s good about the 2.4GHz band?

The 2.4GHz band is the lowest band that is internationally harmonized — it can be used in just about any country throughout the world. This makes it the first choice for almost all commercial products, and is the best choice for a show that is touring internationally.

Are there any disadvantages to 2.4GHz?

2.4 GHz is congested with more general traffic than any other band, since it includes WiFi and Bluetooth, which sometimes reduces reliability for all systems. Performance will deteriorate in very high humidity environments. Signals will not pass through bodies of water including animals and people. The maximum allowed RF power is also lower than in the 900MHz band.

What about the 5.8GHz band?

The 5.8GHz is not ideal for wireless DMX applications for various reasons, but is sometimes deployed as a back-up band for systems primarily operating at 2.4GHz. The 5.8GHz has less congestion than 2.4GHz, but this is unlikely to remain true in coming years. It also uses very small components and very short antenna lengths. It’s also a higher frequency, which y means poorer propagation and range, and the maximum allowed RF power is lower than other bands, further reducing propagation and range. All things considered, the range is substantially more limited than other bands.

What do you like about 900MHz?

The 900MHz band can only be used in the USA, Canada, Brazil, Australia, and New Zealand . Because this is the most limited of all the bands, it is used far less than the others. It is less congested, from an RF perspective, and we expect it will remain that way. Right now, RC4 is the only firm authorized to do wireless DMX in the 900MHz band. In this bandwidth, there is ZERO interference with WiFi, Bluetooth, and all the other technologies that operate in other bands, 900MHz RF signals more readily pass through water and objects, including trees, animals, people, and buildings.

Are there any disadvantage to 900MHz, outside of the limitations of the country you’re operating in?

The RF components for 900MHz products are more costly, and those components are somewhat larger because of the longer wavelength, limiting how small the devices can be. This bandwidth is not recommended for touring productions with uncertain future destinations.

Do all DMX wireless units work the same way in regards to choosing frequencies?

JDS: Not at all. RC4Magic at 2.4GHz uses Direct Sequence Spread Spectrum (DSSS), rather than more common Frequency Hopping Spread Spectrum (FHSS). This is because DSSS delivers the best possible performance in a crowded RF space. The key to better performance using DSSS is a mathematical principle called process gain. The nature of FHSS does not provide significant process gain. Only RC4Magic systems deliver wireless DMX with this important performance advantage.

Where can people find out more about wireless DMX technology?

The RC4 online Knowledge Base has a wide variety of information—from a lexicon of industry specific words to videos and articles. It’s at http://rc4.info/

For an expanded version of this discussion, check out: http://www.theatrewireless.com/rf_bands/

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