iProbe Knowledge Base

the Event Planner's Guide to RF Wireless Simultaneous Interpretation

Published May 6, 2016


this guide helps you evaluate if a simple-to-operate, tour guide style, wireless portable RF system is the right solution for the type of event you are planning. The alternative is a conference interpretation system with a more powerful stationary transmitter.

RF is the acronym for Radio Frequency and FM stands for Frequency Modulated. While the terms RF system and FM system are frequently used interchangebly, and all FM systems are RF systems, an RF system is not always FM. It can for example be AM or FSK modulated. For the purposes of this guide we focus on RF devices which operate as analog systems in the FM band.

dissemination of language interpretation via wireless FM radio transmission is a commonly used technology for the one-to-many meeting model, such as a presentation or lecture, where one person speaks and the audience listens. A variation of this would be a panel discussion with panelists and a moderator. Visiting delegations use tour guide style portable FM systems when they need language interpretation during their trip. These portable FM systems can also be used for meetings taking place in a fixed location.

this guide assumes a basic understanding of meeting planning, conference and simultaneous interpretation setups. If you are new to organizing meetings with simultaneous interpretation, get up to speed with our Beginner's guide to Wireless Simultaneous Interpretation Equipment Rental with a focus on one-to-many meetings.

how FM transmitters work

professional transmitters – both portable and stationary models - operate much like an FM radio station and are a fast and frequently used solution to broadcast simultaneous interpretation via radio waves.

the FM transmitter is connected to the audio source you want to broadcast and an available FM frequency is selected to broadcast the interpretation. The transmitter picks up the live audio directly from the interpreter console or a microphone. Those sounds are then broadcast over an FM radio signal. The audience members in need of language support wear FM receivers, which are tuned to the same frequency as the transmitter to receive a reliable, clear sound signal from the audio source.

in an optimal RF environment, the broadcast can be picked up from a distance of up to 150 ft using a portable FM transmitter and up to 1500 ft using a stationary FM transmitter). An RF environment is considered optimal when:

interpretation systems with stationary FM transmitters

a stationary FM wireless conference interpretation system is configured with:

a stationary FM system is often complemented with one interpreter isolation booth per team of two interpreters assigned to a language direction. In some situations, two interpreters able to interpreter into two-language directions, such as for example English into Spanish and Spanish back into English, share the same booth.

the stationary transmitter has a working range of 750-1500 feet and has the advantage of a flexible configuration for a multitude of audio sources. The transmitter is AC powered and the receivers are battery powered.

illustration showing one way conference interpretation wireless audio flow

One way RF system with a stationary (desktop) FM transmitter, an analog interpreter console and two FM receivers configured for 2 languages. Additional FM receivers can be added at will.

  1. the interpreter listens to the audio feed from the presenters through headphones and speaks the interpretation into a microphone that is connected to the interpreter console.
  2. the audio from their interpretation is fed through the console into the transmitter, which sends a wireless signal with the interpretation audio to each audience member in need of the interpretation.
  3. the interpretation is heard via earphones or headphones plugged into a receiver.

the setup, operation and dismantling of a stationary FM system is typically done by audio visual technicians trained to operate wireless interpretation equipment and referred to as simultaneous interpretation technicians, or SI technicians.

this type of full-service rental is a good solution for events where the meeting organizers prefer to rely on a professional service provider to facilitate a smooth simultaneous interpretation experience.

interpretation systems with portable FM transmitters

The FM system setup can be simplified by eliminating the interpreter console and replacing the stationary FM transmitter with a light-weight, battery-powered, portable FM transmitter, which has a range of up to 150 ft.

the portable transmitter is very similar in shape to the receivers and, just like the receivers, it can be hand held, placed on a hard surface like a table, clipped on the belt, placed in a pocket or carried around the neck using a lanyard.

illustration showing one way portable interpretation wireless audio flow

One way system with a portable (bodypack) FM transmitter and three FM receivers. Additional receivers can be added at will.

this type of setup, frequently referred to as a bodypack FM system, is an economic interpretation equipment rental solution simple enough for someone with limited tech knowledge to operate, without the need for an SI technician.

the ease of use of the portable FM transmitter and the absence of the interpreter console make the beltpack system ideal for interpreters working with a small group, for walking tours and for business groups who travel to different locations with their own interpreter. It can also be a good solution for meetings taking place in a small room. However, the bodypack system has limitations compared to the more powerful and versatile stationary FM interpretation systems and thus is not suitable for all environments and events.

how to determine which FM system is best for your event

The following considerations are a good starting point to determine if a portable RF system could be a good fit for your event and what system configuration you will need for the simultaneous interpretation.

  • meeting format
    • is this a one-to-many type meeting?
    • is this a meeting in a fixed location or will the group be traveling?
    • will everyone be attending the same meeting or will the group be split up into sub groups where each group has different interests and different schedules?

    if you have a small group traveling to various locations, a portable RF system could be optimal. If you're planning a small event in a fixed location without the need for an interpreter console, a portable RF system could suffice. For some events, you might need both a conference interpretation setup with a stationary RF system for the main presentations and breakout rooms as well as a portable RF system for something like a facility tour.

  • audience size
    • how many audience or group members require language support?

    This will determine the number of primary and backup receivers to rent.

  • languages
    • how many languages do I need simultaneous interpretation for?

    this impacts the number of FM transmitters you will need. With an FM system, you need one transmitter per channel. Using an FM transmitter (72 Mhz) the most number of channels – and therefore, transmitters - that will work simultaneously in the same space is six or eight (depending on the brand and model of the system).

    each language direction is normally assigned one channel (example: English into Spanish is one direction, with Spanish into English being another direction). If you want to reduce the number of transmitters you rent, you could assign two language directions to a single channel, providing the two directions are interpreted at different times during the event.

    getting 7 or 8 channels working in the same space with FM 72 Mhz equipment can be challenging. Should you need more than 6 channels, we advise you to contact us to discuss alternative technology options.

  • portability
    • how portable do I need my system to be?

    all systems are transportable, but there is a general trade off between power (i.e. range) and the degree of portability and ease of setup and take down. Ask yourself: is the group in need of language support always in the same room for the duration of the event or will they be having short meetings in multiple locations or go on a tour? A bodypack system can work well for interpreters who accompany a tour group.

  • interpreter and audience location
    • where will the interpreter(s) be set up? At the back of the room? In a separate room or in a sound isolation booth?
    • are the audience members in need of language support in the same room, within 100 feet of the interpreter(s)?

    the working range of a portable bodypack RF transmitter is 100 feet, measured within an "optimal RF environment". You might be able to get up to 150 feet depending on circumstances.

  • floor audio feed
    • how will the interpreter(s) listen to the floor language?

    best practices call for interpreters to use headphones, a microphone and an interpreter console from where they can control the sound level during the event and make adjustments as needed.

    the bodypack RF system does not include an interpreter console, so to isolate the interpreter from noise you will have to provide the interpreter(s) with headphones from the mixing board [link to .../wireless-SI-equipment-rental-for-one-to-many-meetings#headphones-from-mixing-board] or an adhoc wireless audio feed [link to .../wireless-SI-equipment-rental-for-one-to-many-meetings#ad-hoc-wireless-audio-feed]

    while you can have the interpreter listen naturally to the speaker with no headphones and no audio feed, we recommend supplying interpreters with a direct audio feed. Without a dedicated audio feed interpreters are exposed to noise in the room, which will impair their ability to concentrate on the interpretation.

  • Q & A session
    • do I prefer the Q & A in consecutive or simultaneous interpretation mode?

    consecutive mode does not require use of interpretation equipment as the interpreter will go sit next to the presenters, hear the question from the audience, interpret it to the presenter, then listen to the presenter's answer and interpret it back to the audience.

    If you prefer having the Q & A interpreted in simultaneous mode and there is no PA system with a roving microphone or a centrally placed microphone on a stand, you may want to rent an additional bodypack RF transmitter with a plug mic that can be passed around during the Q & A. The interpreter(s) will need receivers with an earphone or earplug to hear the questions and whoever will be answering the question will need their own wireless RF receivers to listen to the interpretation of the questions.Learn more about simultaneous interpretation for Q & A [link to .../wireless-SI-equipment-rental-for-one-to-many-meetings#Q&A]

  • venue
    • is there a clear line of sight between the transmitter and the receiver?

    RF systems can penetrate walls or other opaque objects. However, physical elements (like pillars and walls) made out of metal, thick brick, concrete or masonry blocks between the transmitter and the receivers, might block or reduce the power of the transmission.

    if such obstructions exist, each side of the wall should be treated as a separate deployment space for purposes of coverage calculation since little to no RF energy will be transmitted through the wall. A stationary FM system may work better in this scenario than a belt pack systems.

  • confidentiality
    • Is the event classified as highly confidential? Does your event require security against eavesdropping of the simultaneous interpretation?

    if the content of your presentations is highly confidential and you need to make sure nobody outside of the event can intercept it, contact us to discuss alternative technologies such as digital infrared, which is more secure than radio frequency based equipment.

  • equipment management
    • Do I want the responsibility for the technical planning, onsite operation and management of the interpretation equipment or do I prefer to hire a professional service provider?

    if you rent a bodypack RF system to operate it on your own, in addition to the interpretation you will have responsibility for various aspects of the technical equipment management and operation, including:

    • you decide how many transmitters and receivers you need, what kind of microphones, earphones or headphones and how the interpreter(s) will listen to the floor language.
    • you are responsible for the performance of the technology. This means you should test the system beforehand at the various locations where you plan to use it. We can pre-program to preferred channels within the 72 Mhz band and tune receivers to each channel. However, if you experience interference, you will need to find a clear channel by listening to all the wide band channels.
    • during the event, if you have multiple languages being interpreted, you have to make sure each attendee gets the right receiver. For example, if channel 1 is assigned to English into Spanish language direction, all attendees who need to receive interpretation in Spanish will have to get a receiver pre-set to channel 1 (and so on).
    • you need to make sure the interpreter can hear the floor language throughout the event. It's also a good idea to monitor the interpretation feed in case you need to troubleshoot interference.
    • you may have to replace batteries during or after each day of the event. With new AA Alkaline batteries the bodypack transmitter works for approximately 4 hours and FM receivers last for 30+ hours. As part of the rental, iProbe supplies enough battery power for the expected length of your event.


a bodypack RF system is a cost effective solution to transmit simultaneous interpretation provided certain conditions are met. Some of the discussed variables that can reduce the range or weaken the transmission signal are hard to predict without onsite testing. To warrant a seamless interpretation experience, try to test the bodypack RF interpretation system onsite ahead of time to figure out the actual transmission range you have available.

if you experience dropouts in some areas or on some channels and changing the room layout or the channel doesn't solve the problem, you can contemplate upgrading to a more powerful system and have the technical aspects handled by a professional service provider. Testing in advance will give you enough time to do this.

there is technically no limit to the number of RF receivers that can be used in conjunction with the bodypack RF system, although best results may be achieved in smaller settings with 20-30 attendees in need of interpretation. You can try using the system with more attendees as long as everyone is within the working range of the portable FM transmitter. As you plan the layout of the room try to keep everyone needing language support close to the interpreter and try to test beforehand.

to request a quote or ask a question

call us at 212-489-6035 to speak with a interpretation equipment specialist.

learn more about our interpretation equipment rentals.


*NOTICE: This guide is provided to iProbe customers to help prepare for use of interpretation services and interpretation equipment rental and reduce the possibility of issues occurring at time of event due to improper operation of interpretation equipment by customer or insufficient planning during the event preparation phase. It is NOT intended to be a comprehensive guide for renting interpretation equipment or contracting interpretation or related services. We make no warranties, express or implied, regarding this information. Proper event planning is the sole responsibility of the organizer. For more information and additional guidelines, refer to your contract, or contact iProbe. Refer to the current iProbe Service Guide for terms, conditions, and limitations applicable to iProbe services.