Vector Diversity in Wireless Audio, Explained

Credit: Lectrosonics
Lectrosonics has developed a new way to cope with interference through vector diversity. Let's take a look at what that means. 

When it comes to improving wireless performance, manufacturers often use receiver diversity to improve the reception of RF signals.

Before diving into vector diversity, it's important to get you up to speed on the basics of wireless audio to better understand why diversity is essential to improving the overall signal of wireless audio. 

What Is a Wireless Audio System?

A wireless audio system is generally made up of a transmitter and a receiver. Typically a transmitter is connected to a lav, microphone, or line level signal, and it is sending audio to the receiver over a specific frequency channel. The receiver then typically sends the transmitted audio into a mixer, recorder, or even a camera where it can be captured to a file or played live on air. 

Common wireless systems used in filmmaking include the Sennheiser G4, RØDE Wireless GO II, the Deity Connect System, and many others from Lectrosonics, Wisycom, Audio-Technica, and Zaxcom to name a few. 

While the most basic setup includes a single transmitter and a single receiver, larger wireless setups can include multiple transmitters and receivers. No matter how large the setup, the wireless signal is transmitted over a specific frequency channel. In the United States, that frequency spectrum is governed by the Federal Communications Commission (FCC). 

The FCC licenses certain frequency channels for companies to develop wireless audio systems for filmmakers. Over the years, the FCC has been auctioning off large chunks of available frequencies to mobile provides and cable companies. Those auctions include the elimination of the 700 MHz and 600 MHz bands. As the number of available frequencies continues to shrink, it increases the chances of radio frequency (RF) interference when you're out in the field. Wireless audio companies are finding new ways to combat the shrinking spectrum, including developing wireless for the 900 MHz band and unlicensed 2.4GHz band. 

Let's take a stop at what the frequency spectrum is. 

What Is the Frequency Spectrum?

Wireless devices transmit signals on a frequency band. Generally, it's either on the VHF, UHF, or 2.4GHz spectrum. Though the wireless spectrum is much larger, the frequencies designated for wireless microphones, in general, are as follows:

  • Low-band VHF 49-108 MHz
  • High-band VHF 169-216 MHz
  • Low-band UHF 450-806 MHz
  • High-band UHF 900-960 MHz
  • 2.4GHz band 2.400 GHz-2.483 GHz

With each frequency band, there are a certain number of channels that a wireless system can use to transmit a signal. You'll see certain manufacturers say their wireless audio system is wideband, which means it offers more of the available frequency spectrum in the model. Wideband wireless systems are generally better, as you get more frequency channels. 

It's also worth noting one reason why 2.4GHz wireless audio systems are cheaper is because they do not need to go through the red tape of being approved by the FCC. It costs the companies money to develop wireless in the UHF and VHF band, which can influence the overall price of the product. 

If you're wondering which of the VHF, UHF, or 2.4GHz bands is better, we got you covered. 

Is VHF, UHF, or 2.4GHz Better?

While there are many technical details of each, like wavelength characteristics, here's what you need to know.

  • The entire spectrum is shared by different users and different devices 
  • All signal types whether analog or digital can suffer from interference

Low-band VHF 49-108 MHz
Except for things like assisted listening systems and walkie-talkies, don’t consider this frequency band for serious wireless applications. It’s very prone to interference among other things. Devices like Comtek use the frequency band with great success. 

High-band VHF 169-216 MHz
This frequency band is better than low-band VHF, as it has less interference. It’s ideal for small locations or when you have a good line of sight. It’s also capable of penetrating thinner walls, and it's decent for car work, but it works best with shorter distances. Again, Comtek systems utilize the 216 MHz.  

Low-band UHF 450-806 MHz
Flat out, this is the best frequency band available for wireless systems. It offers the most range, widest dynamic range, better power output over VHF, and the most channels. The physical size of UHF wireless can be significantly smaller too. While prone to interference, it suffers the least and can penetrate through walls with the most efficiency.

Typical wireless microphones in the U.S. will operate between 470-600 MHz.

High-band UHF 900-960 MHz
This frequency band offers similar characteristics to low-band UHF, but the number of channels is limited. Typical wireless in the U.S. will operate between 941-960 MHz. 

2.4 GHz band 2.400 GHz-2.483 GHz
This is a crowded spectrum. Bluetooth, internet, cordless phones, security systems, and smartphones run WiFi. Channel counts are usually limited, as is the range of the wireless. Latency can also be a bit higher than UHF systems. However, companies like Deity are changing the way 2.4 GHz wireless systems typically work, offering better power output and less interference. These systems are worth considering for less demanding applications.

So now that you know the basics of a wireless audio system and how it transmits audio, let's talk about the technology that allows for better wireless performance. 

Lectrosonics SRc & SRc5P are diversity receivers

What Is a Diversity Receiver?

When it comes to improving the wireless signal, wireless audio systems use diversity receivers. In its basic form, a diversity receiver uses two separate antenna systems. This allows the receiver to choose which signal coming from the transmitter is stronger and automatically switches to the more robust signal, and thus, prevents any drops in audio. 

There are many ways a company can deploy a dual-antenna diversity system in a receiver. Common techniques include antenna switching, phase switching, and true diversity. This is where vector diversity from Lectrosonics comes in. It's a new way to optimize receiver performance with the hope of creating fewer dropouts.

Let's take a look at each diversity type. 

Antenna Switching Diversity
This diversity system, also known as space diversity or spatial diversity uses one antenna at a time. With wireless audio, each antenna will be set to a different interference environment. The receiver will automatically switch to the other antenna when one experiences interference. 

Phase Switching Diversity 
In phase switching, the two antennas work together. The signal from the antennas either in phase or out of phase switch depending on which combination provides the stronger signal. This is generally better than antenna switching when it comes to wireless audio systems. 

True Diversity 
When it comes to diversity, true diversity, which can sometimes be called ratio diversity or audio switching diversity, has become the de facto industry standard. A true diversity system has two independent receiver sections, each with its own antenna. Meaning, instead of two antennas and a single receiver, there are two receiver sections with their own antenna. This makes for a very stable signal but can drive up the cost of the unit. 

Vector Diversity 
Vector diversity is very much like true diversity, as it uses two receiver channels and two antennas, but according to Lectrosonics, it adds the additional process of phase-aligning the two signals before combining them. This isn’t as critical for analog RF sources, but for digital, it makes a big difference due to the cliff effect. 

With all digital systems, their signals do not degrade gradually. Instead, they deliver great performance and then fall off a cliff. It's kind of like the ending to Thelma & Louise. One minute they're driving on a dusty road, the next minute they're taking a nose dive into a canyon. Because of that, true diversity may not be the end-all solution for digital wireless. 

According to Lectrosonics, vector diversity "works by expressing the signal from each antenna in vector form (angle and magnitude)." By doing so, Lectrosonics says it makes it possible "to continuously rotate one of the vectors mathematically so the angles match and the signals can be combined constructively." This makes it so the energy from both antennas is contributing to receiver performance. 

Lectro does this by incorporating two complete receivers, converting each antenna's signal to a vector at an intermediate frequency in the digital domain. These vectors are then rotated and combined optimally, then demodulated. And boom, you have vector diversity. 

The Lectrosonics DCR882 receiver uses vector diversity Credit: Lectrosonics

Summary

While users may not see a drastic change in performance when it comes to vector diversity in analog wireless systems like Lectro's Digital Hybrid System, when it comes to digital technology, it can be the make-or-break in improving audio drops. You can find vector diversity technology inside Lectro's Digital Wireless series, including the new DCR822 receiver. 

Have you had any experience with the new tech? Let us know your thoughts in the comments below.      

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