16th in a series.
While we can’t directly see or hear a radio frequency with our own eyes and ears, they might arguably be the most important communication tools we have today. But despite their omniscient role in classroom and presentation settings, too few people understand the differences between these frequencies, and where each is used by PA equipment.
There are three commonly used communication frequencies by portable PA gear and installed classroom amplification systems; “Ultra High Frequency” (UHF), “Very High Frequency” (VHF), and “Infrared” (IR).
UHF is commonly used for televisions, cell phones, two-way radios, global positioning systems (GPS), and is considered to be any radio frequency whose range falls between 300 MHz (Mega Hertz) to 3GHz (Giga Hertz). A UHF wavelength ranges from one to ten decimetres (10 cm to 1 meter, or 4” to 39”). From a presentation perspective, most portable PA equipment (including most of those offered by Califone) uses the UHF band. A signal in this range does not have to be strictly line of of site (ie. a clear unobstructed path from the transmitter to the receiver). The signal can be strong enough to travel through solid walls, but this can have an effect on its quality however.
A classroom wide audio amplification system using an infrared frequency (left) or a portable system using UHF (center) or VHF (right) or a classroom boombox with a built-in infrared transmitter (far right)
The VHF range is between 30 MHz – 300 MHz, and is primarily used by FM radio and television broadcasting. Compared to UHF, VHF is less affected by buildings or other smaller objects, but is less commonly used by PA systems. There are two Califone products use this frequency. The PA Pro is a portable (handheld) 10W PA which uses a wireless mic. The Wireless Listening System is a transmitter which connects to any audio player and transmits its signal to listeners with dedicated headphones within a 100’+ range
Infrared (IR) radiation occupies a part of the electromagnetic spectrum with a frequency less than visible light and greater than most radio waves. Unlike UHF or VHF transmissions, IR cannot be transmitted through solid walls so it won’t interfere with other devices in adjoining rooms. Since this type of signal is typically contained within a single room, it is often used for shorter communication ranges such as indoor remote controls and by Classroom Audio Systems (the signal can break up if exposed to direct sunlight). An infrared signal relies on a clear line of sight path from the transmitter to the receiver for a clear signal.