RF Basics

The RF Basics series describe the fundamental building blocks of wireless systems. They are designed to be read in order. They should help if you are new to wireless systems, or to provide a refresher if you are experienced. However you use them we hope you feel more confident after reading them.

How RF gets audio signal from A to B?

All radio frequency (RF) systems have a transmitter (TX) and receiver (RX). Transmitters and receivers can take many forms including handheld, beltpack, rack mount or desktop.

Regardless of how they look, all audio RF systems take in an audio signal, attach it to an RF carrier wave at the transmitter, transmit the signal to the receiver where the RF carrier wave is detached from the audio allowing the audio to be sent to the audio output and into the audio system.

Form Factor
With RF microphones, the microphone (or beltpack the microphone connects to) is the transmitter and the receiver is, typically, a stationary unit with an audio output. With in- ear monitors (IEM), the transmitter is, typically, a stationary unit with an audio input and the beltpack the headphones connect to is the receiver. The notable exceptions to this rule are RF systems used in film and broadcast where, to save space and weight both the RX and TX units may be the size of a beltpack.

Antennas
All RF systems require an antenna. Depending on the size of the device these may be obvious or hidden. On handheld microphones the antenna is normally integrated into the handle. On beltpacks, whether a microphone TX or IEM RX, the antenna is normally a small piece of wire protruding from the device. On the normally stationary parts of the system, the antennas connect to the back or the front with BNC connectors. BNC connectors are keyed so that the ring uses the pins to locate the connection, requiring a 90 degree turn to lock them in place.

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Essential: The components that every wireless system needs are a transmitter, receiver, antenna, and antenna cable (for remote antennas).

Transmitters (TX) - Combine the RF and audio signals and transmit the audio signal to a receiver.

Receivers (RX) - Receive the combined RF and audio signal and remove the audio routing it to an audio output. Depending on the system, outputs can be balanced (XLR or 1⁄4” TRS jack), unbalanced (1⁄4” TS jack) at line level or mic level & headphones in mono or stereo.

Antennas - Broadcast & receive the RF signal. There are 3 different types normally used depending on the coverage and gain required. From lowest gain and widest coverage these are - Omnidirectional, LPDA (aka Shark Fin or Batwing), & Helical.

Whip antennas can mount directly to a receiver or transmitter. These antennas are included with many systems.

Antenna Cable - Not all coaxial cable is suitable for use with wireless audio equipment. Coaxial cable used with wireless audio systems should be 50 Ohm cable. 50 Ohms is the impedance of the cable and is the standard for these RF systems. All coaxial cable introduces some amount of RF signal loss. Generally, signal loss increases at higher frequencies and longer distances. Loss of signal due to cable length may make the difference between a stable, usable system and one that experiences drop outs.

Supplemental: Equipment used to expand wireless systems such as amplifiers, RF filters, passive splitter/combiners, distros, and active combiners.

Amplifiers - An RF amplifier raises the gain of RF signal to compensate for loss due to distance or using passive splitter/combiners.

Filters - These devices filter out unwanted RF signal. This lowers the overall RF noise floor and can improve receiver performance.

Passive splitter/combiner - These devices allow a number of RF signals to be split or combined passively. There is a loss in RF gain when used (see RF signal gain and loss).

Antenna Multicouplers - Often called distros, splitters, or active splitters. Multicouplers take the RF signal received by an antenna and distribute it to multiple receivers. They are most commonly used with wireless microphone systems.

Combiners - An RF combiner accepts signals from multiple TX units (IEMs for example) and combines them together, allowing multiple TX units to feed a single antenna. Combiners are commonly used with IEM and IFB systems.

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How to use one set of antennas to send RF signals to multiple microphone receivers?

As described in “How do RF Systems work?” all RF systems are composed of a transmitter and receiver. We will now look at how multiple wireless mics can work together in one RF system. When using four or more wireless mic systems together it is better to use one set of antennas, mounted in a position advantageous for reception, rather than trying to cram all the antennas supplied with the microphone systems in one place. When trying to place four or more sets of whip antennas in a rack or on a table top it becomes difficult to make certain that each set is oriented correctly to ensure maximum reception.

A single set of antennas can be distributed to multiple receivers using an antenna distro. Using one set of antennas ensures they can be oriented for maximum reception. Each receiver is receiving the same signal as if it was connected directly to the main antennas. This system is scalable depending on the number of receivers and number of outputs on the distributor. If additional distribution is needed, a master distro can be used to feed multiple secondary distro units. PWS sells distributors which can distribute signal to 8 receivers from a single 1RU distro.

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