Listen Technologies 863.200, 863.400, 863.500, Stationary FM 863 MHZ User Manual

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Assistive Listening • Language Interpretation • Soundfi eld • Tour Group • Conferencing

Stationary FM Table of Contents

Design Guide
FM Technology Overview 5
System Overview 6
Key Concepts in Designing an FM System 8
Notes 17

LT-800-863 Stationary FM Transmitter
Specifi cations 25
Block Diagram 26
Quick Reference 27
Setup Instructions 28
Operating Instructions 30
Accessories 34
Notes 35

LR-400/500-863 FM Receivers
Specifi cations 45
Block Diagram 47
Quick Reference 48
Setup Instructions 50
Operating Instructions 53
Programming Instructions (LR-500 only) 59
Accessories 60
Notes 61

Design Guide

LT-800

Supplementary Information
Battery Charging Information 69
Frequency Chart 70
Troubleshooting 71
Frequently Asked Questions 73
Compliance, Warranty and Contact Information 75
Notes 76

LR-400/500

Supplementary

Stationary FM Design Guide Table of Contents

Table of Contents 3
Technology Overview 5
System Overview 6
Key Concepts in Designing an FM System 8
Notes 17

Design Guide

3

Frequency Modulation (FM) Technology Overview

Frequency modulation or (FM) is a means of transmitting audio using electromagnetic waves.
This same technology is used by local FM radio stations to broadcast music. FM signals can travel through
most barriers – walls, fl oors, and ceilings. The distance a signal travels has many different variables such as
Radio Frequency (RF) output power, the type and placement of the antenna, and the broadcasted
frequency. Unlike infrared, FM transmission are not secure. This enables a receiver to travel further distances
from the source. This section of the manual will help you design a system that will get the best range and least
amount of interference.

FM Receiver

Audio Source

FM Transmitter

When designing an FM system it is important to keep the following in mind:

Design Guide

• Multipath

Multipath interference is a form of RF interference that occurs when radio signals have more than one path
between the receiver and the transmitter causing the two RF signals to add out of phase. This could occur in areas with

RF-refl ective surfaces, such as furniture, walls, or fl oors. The result of multipath is the receiver audio coming in and out of
squelch when the receiver is moved. Portable applications are much more susceptible to multipath than those that are
stationary. Multipath distortion is often worse as the distance between transmitter and receiver increases

(RF power decreases). Multipath can decrease the audio quality of the transmission.

• Antenna placement

The antenna should be placed as high as possible and in line of sight of the receivers. The antenna should not be

mounted near metal objects. Keeping the coaxial cable as short as possible will also limit the loss of RF power.
The LT-800 comes equipped with an articulating right angle dipole antenna (LA-129). The remote antenna kit
(LA-130) is an optional accessory. The antenna on the receivers should always be in the upright position to maximize

the transmission range. Placing the antenna in areas where the RF cannot properly be transmitted will limit the range

of transmission.

5

System Overview

Design Guide

There are four main parts to a Stationary FM system – transmitter, antenna, receiver and input source, .

LT-800-863 Stationary FM Transmitter (863 MHz)

Input source

LA-129 90° Articulating Antenna (863 MHz)

(Included with Transmitter)

Input Source

The input source can be audio from a sound board, microphone or a personal audio source like a CD player,
MP3 player, computer, DVD, etc. Audio will be Connected into the audio inputs of the stationary transmitter.

Transmitter

The LT-800 transmitter modulates the audio on an FM carrier and transmits the signal via an antenna.

LR-400-863

Portable Display FM

Receiver (863 MHz)

LR-500-863

Portable Programmable

Display FM Receiver

(863 MHz)

LA-129

6

LA-130

LT-800

System Overview

Antenna

There are a several options for antennas. Antennas can either be back-mounted on the
unit or remote mounted.

LA-129 90° Articulating Antenna (863 MHz)

(Included with Transmitter)

Design Guide

LA-130 Remote Antenna Kit (863 MHz)

Receivers

Listen offers two different portable receivers: the LR-400 and LR-500.

LA-131 Antenna Kit for Rack Mount (863 MHz)

LR-400-863

Portable Display FM

Receiver (863 MHz)

LR-500-863

Portable Programmable

Display FM Receiver

(863 MHz)

7

Key Concepts in Designing a Stationary FM System

Input Selection

Design Guide

The LT-800 has two audio input options: Input 1 and Input 2. Input 1 is a balanced connection using either an XLR or ¼”
phono connector, and input 2 is two unbalaned phono connectors. Use Input 1 if you are using a microphone or if you
have a balanced connection such as from a professional audio mixer (you can also use Input 1 for unbalanced con­nections). Use Input 2 to connect to an unbalanced audio source.

Balanced XLR or
1/4” phono connector

Unbalanced right
and left phono
connectors

Input 1: Connect the audio source(s)

Connect the audio source(s) to one or both audio input connections. Input 1 offers a choice of balanced
XLR or ¼” phono connector. Plug your microphone into Input 1 and move the input select switch to Mic (for
dynamic microphones) or Mic + PH Power (for condenser microphones). A feed from a soundboard can also
used with Input 1. Be sure the input type selected (line, mic or mic-PH PWR) matches with the output type. The
following is a wire diagram for Input 1 balanced and unbalanced connections:

1/4”Phone Wiring

Balanced

Sleeve

Top Ring Top Ring/Sleeve

Balanced

Audio

Source

Tip

Ring

Sleeve

Audio from

Unbalanced

Unbalanced

Audio

Source

Balanced

Audio

Source

XLR Wiring

Input from

Unbalanced

Audio

Source

8

Key Concepts in Designing a Stationary FM System

Input 2: Connect the audio source(s)

Plug your unbalanced audio source into Input 2 and select the audio level switch for -10 dBu or +10 dBu to
match the audio level coming from your equipment.

Using Two inputs

The LT-800 can accommodate two inputs simultaneously with the use of the input level potentiometer.
When two inputs are present, both sets of input level lights will be activated.

Design Guide

Mix Level

The mix level acts as the “master transmit” control. It will increase the transmit gain on the “mix” of the two
levels (if two levels are in use).

Input Level Knob

Mix level adjustment

9

Key Concepts in Designing a Stationary FM System

Selecting Transmitting Frequencies

Design Guide

Use this section of the guide to choose the channel settings for the transmitter and receivers.

Testing System

Find transmission channel(s)

The goal is to fi nd a transmission channel(s) that is free from interference. Interference comes from other
transmitters and from other equipment (such as a computer).

Listen’s LT-800-863 o ers 17 di erent channels to choose from

Listen’s LT-800-863 offers 17 different channels to choose from. This increases the chance you’ll fi nd an
interference free channel. The best way to check for interference is to turn a receiver on and press the SEEK
button. If there are any channels with interference, the receiver will fi nd these channels. Do not transmit on
these channels.

Monitor Jack

The headphone jack is used to monitor the mix of input 1 & 2. You can adjust the monitor level with the volume
knob. The headphone jack is a standard 3.5 mm jack.

Test Tone

Use the test tone to transmit a 400 Hz tone. This tone will allow the end user to know if the system is transmitting
properly. All receivers should be able to hear this tone if tuned to the proper channel.

10

Headphone
monitoring jack

Test Tone Button

Key Concepts in Designing a Stationary FM System

Antenna placement (rear or remote)

Rear mounted antenna

Rear mounting the LA-129 90° Articulating Antenna (863 MHz) will allow the transmitter to be moved if necessary.

Design Guide

Remote antenna

The LA-130 Remote Antenna Kit connects to the LT-800 and can be placed away from the transmitter for better
range. It also allows the unit to be rack mounted with the antenna remotely using the LA-326 Universal Rack
Mounting Kit. The LA-130 comes with 25’ of black coaxial cable (RG-58)

ATTENTION: Long cable runs can result in signal degradation due to the “loss” characteristics of

the cable. Minimize cable runs as much as possible or use “low loss” RG-8 cable.

11

Key Concepts in Designing a Stationary FM System

Front of the rack mounted antenna

Design Guide

The antenna can also be in the front of the rack with the use of the LA-131 Antenna Kit for Rack Mount
(863 MHz) and the LA-326 Universal Rack Mounting Kit.

Maximizing Transmission Range

For proper and dependable operation, Listen receivers need to receive a strong and consistent signal from the
originating transmitter. The following strategies should be used maximize this signal:

Transmitting and receiving antennas

When designing and installing your system, keep in mind that the location of both the transmitting and
receiving antennas is critical to maximize broadcast range. Eliminate or minimize obstructions between the
transmitting and receiving antenna. Minimize the distance between the transmitting and receiving antennas.
Move transmitting and receiving antennas away from metal or conductive objects.

Antenna Placement

Place the transmitting antenna as high as possible. The antenna should always be oriented upwards. If the
height of the antenna exceeds 7.6 m (25 ft.), the antenna should be placed with the radial facing downward
(as shown in diagram).

CAUTION: When installing antennas, ensure the antenna is clear of power lines.

12

Key Concepts in Designing a Stationary FM System

Orientation

Orient both transmitting and receiving antennas vertically.

RF Power switch

Position the RF Power switch on the back of the LT-800 to full RF Power, unless lower power is necessary.

Design Guide

RF Power Switch

Cable Length

Keep coaxial cable from transmitter to antenna as short as possible.

13

Key Concepts in Designing a Stationary FM System

Mounting Transmitter

Design Guide

The LT-800 can be rack mounted if necessary. With the use of the Listen LA-326 Universal Rack Mount Kit, you
can mount one or two transmitters to the standard 19” rack. The rack mounted unit will take 1 ru of space.

Rack Mount with dual units installed.

Rack Mount with single unit installed.

NOTE: The antenna may need to be remote mounted using the LA-130 Remote Antenna Kit if the
transmitter(s) is rack mounted. If a rack is metal, it is not recommended to have the antenna inside. Also,
the depth of the rack and equipment inside could prevent an antenna from being placed inside.

The LA-131 rack mount accessory will allow you to place your LA-129 antenna at the front of the rack. Having
the antenna in the front will give better reception range.

14

Key Concepts in Designing a Stationary FM System

Multiple Channels

Guidelines for multiple channels in multiple and single spaces.

Example #1

A museum patron walks to an exhibit and needs to listen to one channel at a time.

In general, such systems work very well because of what is called “capture effect”. A Listen receiver will lock
onto or “capture” the strongest FM signal. If the receiver is near a dominating transmission signal, it will ignore
other interference – even if it is on the same channel. In theory, you can have an infi nite number of
transmitters operating in this scenario. However, to reduce the possibility of the receiver accidentally receiving
interfering transmissions, use the following guide lines:

• Reduce the transmission power on the rear of the LT-800 Stationary Transmitter to the lowest level possible.

• Get the transmitting antenna as close to the receivers as possible.

• Increase the squelch threshold on the receivers if necessary.

• Choose adjacent broadcast channels with the highest channels spacing. Try to get the channel spacing to
be at least 300 KHz apart.

• Receiver DX and Local –

DX Mode – Both strong and weak channels will be automatically tuned. This will increase the range of

the transmission.

Local mode – Only strong channels will be automatically tuned in.

Design Guide

15

Key Concepts in Designing a Stationary FM System

Example #2

Meeting participants need to select any one of, say, four language interpretations of the meeting.

Design Guide

• In general, space the channels as far as possible from each other. For example, if four channels are needed
from transmitting signals, using channels 1, 4, 8, and 12 would be recommended (please see the channel/fre­quency chart on page 70 for the list of frequencies).

• Space the antennas at least one wave length from each other. A wave length at 863-864 MHz is 33 cm (13 in.).

• In these applications, it would be benefi cial to use the LR-500-863 Portable Programmable Display FM Receiver
(863 MHz) to “lock out” any unwanted channels. The receiver would only see the frequencies currently being
used within the room.

• DX and Local mode can be used for the receiver to SEEK and fi nd only the strongest signals.

16

Spanish

French

Chinese

English

Notes

Design Guide

17

Notes

Design Guide

18