Shure Whiteboard - Increased Spectral Efficiency with HD Mode
In this month's Whiteboard Session, Shure Applications Engineer, Tom Colman explains how high-density mode allows us to take the spectral efficiency of digital wireless to a whole new level. Read the article below, or scroll down to watch the Whiteboard Video.
As we've determined in previous sessions, digital wireless systems are typically more spectrally efficient than analogue wireless systems. In other words, a digital transmission often takes up less RF spectrum, and therefore we can fit more transmissions into a given portion of spectrum at a given time. With ULX-D, we can take this one step further by using high-density (HD) mode.
In standard mode, a Shure ULX-D wireless system will comfortably operate between 17 and 22 transmissions within an 8MHz band TV channel. To obtain this performance, the RF engineer will typically deploy an output power of around 10mW, with 200KHz of output bandwidth and channel-to-channel spacing of 350KHz.
However, we can take this efficiency even further by reducing the output power to 1mW, limiting the modulation bandwidth from 200KHz down to 100MHz, and lastly, by reducing the channel-to-channel spacing from 350 to 125KHz. Collectively, these operating principles are referred to as High-Density mode, which enables us to run up to 63 transmitters in a given 8MHz TV channel portion of spectrum. (That's over 500 compatible channels within an entire tunable bandwidth).
HD Mode does reduce the operating range, and therefore, is not suitable for applications where the typical range is required — say a live stadium gig for example. HD Mode is best suited to more contained RF conditions, such as tradeshows and conference events, or corporate office facilities. The reduced output power, in particular, makes HD-mode perfect for these busy, zoned events, where reduced signal range is actually desired to help contain sets of wireless kit within a given portion of the venue. Best of all, the audio quality is unaffected by switching from standard to HD transmission; we still retain a full 20Hz to 20KHz frequency range for all transmissions.
As demand for RF spectrum continues to increase, the role we play as sound engineers is imperative. It's important we stay up-to-date with the latest technology to make the best of the spectrum available. To learn more about best practice wireless operation — including how digital wireless systems play a huge role through spectral efficiency — consider attending one of our Shure Wireless Mastered seminars. To register or find out more, visit the Shure Audio Institute section of our website.