Wireless Microphones: UHF and VHF
The benefit of wireless microphones
Wireless microphones free you from being tethered to cumbersome audio equipment giving you the ability to move about during a performance or engage your audience in a way that otherwise would take a very long microphone cable. Wireless microphones also eliminate tripping hazards as well as simplify set up and tear down as there are no cables to wrangle and detangle. You may find wireless microphones in a number of different designs in fact there are just as many wireless microphone designs as there are wired mics as almost all wired microphones can be converted into a wireless system with the implementation of a transmitter such as the SKP 100 G3 plug-on transmitter which can be found in the Sennheiser EW100ENG G3 wireless microphone pack pictured above.
How They Work
Wireless microphones use two major components. The first being a transmitter which operates like a little radio station transmitting anything the microphone picks up. The Second being a receiver which just like the radio in your car receives the radio signals from the transmitter and converts them into a line level audio signal to be amplified or recorded.
The radio signals are broadcast using frequency modulation (FM) which is a process of encoding the audio being transmitted in a carrier frequency using phase variance. This is exactly the way the FM dial on your car radio works. There is another process used less often for this application called amplitude modulation (AM) which uses varying levels of signal strength or amplitude to encode the audio. If that sounds familiar it’s because that’s exactly how your AM dial on your cars radio works. Depending on the manufactures design the transmitter and receiver may have only a fixed carrier frequency on which they operate or variable frequencies that can be selected based on the available of frequencies in a particular area.
In order to truly understand this process it’s important to understand how radio signals are broadcast. Radio waves are waves of electromagnetic radiation that oscillate or vibrate back and forth a number of times in a second. The term “frequency” simply states how “frequently” the electromagnet wave vibrates in a second. We use Hertz (Hz) as a standardized unit of measurement for all broadcast applications. This is named after Heinrich Rudolf Hertz, the German physicist that first demonstrated the existence of electromagnetic radiation in the mid 19th century.
That being said there is only a finite amount of “bandwidth” which wireless microphones can operate on. Bandwidth is a term used to describe the range of carrier frequencies the transmitters and receivers can use i.e. the amount of information that can be transmitted.
The range of the available bandwidth can be seen in this image of the electromagnetic spectrum where youll notice the two classifications of available bandwidth VHF (very-high frequency) and UHF (ultra-high frequency). VHF ranges from 30 MHz to 300 MHz meaning 30 million oscillations per second to 300 million oscillations per second. UHF ranges from 300 MHz and 3 GHz meaning 300 million oscillations per second to 3 billion oscillations per second.
UHF vs. VHF
Due to the higher frequencies UHF equipment use physically smaller waveforms meaning the receiver anteni can me much smaller making UHF receivers much more compact. The downside is the smaller waveform carries less energy so the operating range of the system may not be as great as a VHF system. For this very reason the FCC (Federal Communications Commission) allows for UHF transmitters to be more powerful. This is great but as a side effect battery life may be sacrificed. The FCC limits transmitter power of UHF equipment to 250mW compared to VHF 50mW limit. Given the larger VHF wave these systems have more ability to punch through walls and their designs typically yield longer battery life.
So what does this all boil down to? UHF systems are typically the choice of professionals for higher fidelity and operating range due to power regulations. VHF is often chosen as an option for situations where direct line of sight isn’t an option as the waves can punch through obstacles.