Listen Technologies Portable FM 863 MHz Guide

Dear Valued Customer,
Thank you for choosing Listen! All of us at Listen are dedicated to providing
you with the highest quality products available. We take great pride in their
outstanding performance because we care that you are completely
satisfied. That’s why we independently certify them to the highest quality
standards and back them with a limited lifetime guarantee. We stand ready
to answer any questions you might have during installation or in the operation
of our products. Should you experience any problems whatsoever with your
Listen products, we are ready to help you in any way we can with prompt,
efficient customer care. Because at Listen, it’s all about you! And should you
have any comments on how we might improve our products or our
service, we’re here to listen.
Here’s how to reach us:
+1.801.233.8992
+1.800.330.0891 North America
+1.801.233.8995 Fax
[email protected]
www.listentech.com
Listen Technologies GmbH
Jasminstr. 16
905 22 Oberasbach, Germany
[phone] Tel
[phone] Fax
www.listentech.de
[email protected]
Thank you and enjoy your listening experience!
Best regards,
Russell Gentner and the Listen Team
Listen’s full-time technical support is passionate about what they do and you can depend
on them to solve any equipment issues with confidence. In the few instances where repairs
were needed, 99% of all clients indicated that they were happy with repair
turn-around-times and 85% of the time, clients were without their product for
less than 10 days!
Overall client satisfaction of working with Listen was rated 4.8 out of 5.
Assistive Listening • Language Interpretation • Soundfield • Tour Group • Conferencing
Lifetime Warranty – the best in the business!
“Please continue with your excellent attitude toward customer satisfaction. You guys
are great!”
“I’ve never had such good service from any company. Keep up the good work!”
“You stand behind your product wonderfully.”
The Word Around Listen

Design Guide LT-700 LR-400/500 Supplementary
Design Guide
FM Technology Overview 5
System Overview 6
Key Concepts in Designing an FM System 8
Notes 10
LT-700-863 Portable FM Transmitter
Specifications 17
Block Diagram 18
Quick Reference 19
Setup Instructions 20
Operating Instructions 23
Programming Instructions 25
Accessories 28
Notes 29
LR-400/500-863 FM Receivers
Specifications 37
Block Diagram 39
Quick Reference 40
Setup Instructions 42
Operating Instructions 45
Programming Instructions (LR-500 only) 51
Accessories 52
Notes 53
Supplementary Information
Frequency Chart 61
Battery Charging Information 62
Troubleshooting 63
Frequently Asked Questions 65
Compliance, Warranty and Contact Information 67
Notes 68
Portable FM Table of Contents

3
Design Guide
Portable FM Design Guide Table of Contents
FM Technology Overview 5
System Overview 6
Key Concepts in Designing an FM System 8
Notes 10

5
Design Guide
Frequency Modulation (FM) Technology Overview
Frequency modulation (FM) is a means of transmitting audio using electromagnetic waves.
This same technology is used by local FM radio stations to broadcast voice and music. FM signals can travel
through most barriers – walls, floors, 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. This section of the manual will help you design a system that will get the best range with the least
amount of interference.
Microphone
FM Transmitter Receiver
When designing an FM system it is important to keep the following in mind:
• 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-reflective surfaces, such as furniture, walls, or floors. 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 (refer to page 9 for
strategies on eliminating multipath).
• Antenna Positioning
For full RF functionality of the portable system, the antenna on both the LT-700 transmitter and receiver (LR-400/500)
must be in the upright position (shown below).

6
Design Guide
System Overview
There are three main parts to a Portable FM System – Input source, transmitter, and receiver.
A microphone is the most common input source for the LT-700 transmitter, although, the LT-700 can transmit
two audio inputs at once on one transmission channel. With the use of the LA-263 both the inputs will be mixed.
Thus, a person can use a line input source and mic source.
Input Source
LA-278
Behind-the-Head Microphone
(other microphones available)
3.5mm Phone Wiring
+ Tip
+ Ring
-
- Sleeve
Unbalanced
Mic input
Line input
LR-500-863
Portable Programmable
Display FM Receiver (863 MHz)
LR-400-863
Portable Display FM
Receiver (863 MHz)
LT-700-863
Portable Display FM
Transmitter (863 MHz)

7
Design Guide
System Overview
Listen offers two different portable receivers.
Receivers
LR-500-863
Portable Programmable
Display FM Receiver (863 MHz)
LR-400-863
Portable Display FM
Receiver (863 MHz)
The LT-700 modulates the audio on an FM carrier and transmits the signal via an anten-
na on the unit.
Transmitter
LT-700-863
Portable Display FM
Transmitter (863 MHz)

8
Design Guide
The range of a portable transmission will vary from one application to another. There are many different
obstructions that could minimize the range. In most applications, the range will be approximately as shown
below (P= Power Level - refer to page 26 for programming power levels of the LT-700).
P1 – 30 meters (100 ft)
P2 – 46 meters (150 ft)
P3 – 61 meters (200 ft)
Range varies depending on environment.
Maximizing Range
Here are some tips to maximize the transmission range:
• Eliminate or minimize obstructions between the transmitter and receivers.
• Minimize the distance between the transmitter and receivers.
• Move transmitter and receivers away from metal objects.
• Orient both transmitting and receiving antennas vertically.
Key concepts in designing a portable FM system
Use this section of the guide to choose the channel settings for the transmitter and receivers.
• The goal is to find a transmission channel(s) that is free from interference. Interference originates from
other transmitters and from other equipment (such as a computer).
• Listen products offer 17 different channels to choose from. This increases the chance you’ll find an
interference free channel.
• The best way to check for interference is to use the “SEEK” button on the receiver. Be sure all Listen
transmitters have been turned off if there is interference, the receiver will find these channels.
If the receiver finds a frequency in use, do not use this channel.
• In general, most of the channels will be free from interference.
• Interference can be overcome by maximizing the transmission power and by using the receivers close to
the transmitting antenna.
• If more than one channel is in use, space the channels further from each other. Use the Listen frequency
chart on page 61 to determine the appropriate channels.
Channel Selection
Range
EXAMPLE: 2 channel system use channels 01 & 11
3 channel system use channels 01, 06 & 11

9
Design Guide
Key concepts in designing a portable FM system
As mentioned on page 5, multipath can occur with portable RF systems. The audio quality of the
transmission can decrease with the occurrence of multipath. Here are a few potential improvements that
can help if multipath takes place:
Eliminating Multipath
Squelch
Squelching the receiver will mute the audio output when the signal from the transmitter is turned off or
the signal is too weak to be received. Without squelch you would hear radio noise in your earphone with
no RF signal present. “Tightening” the squelch will turn the receiver off if it is chattering because of
multipath (refer to page 48 for programming squelch). Keep in mind, “tightening” squelch will limit the
range between transmitter and Receiver.
Transmitter power level
The RF power level can be adjusted on the LT-700 (refer to page 26 for programming LT-700 power levels).
The lower the power setting, the less range the transmitter will broadcast. Decreasing the broadcast range
will force the receivers to remain closer to the transmitter. To maintain an RF signal, the higher power
settings will increase range between transmitter and receiver thus introducing a higher probability of
multipath.
Multiple Portable Systems
In some applications, there will be more than one RF transmission in the same general vicinity.
Intermodulation interference can occur if the transmission frequencies are too close together. Here are
some ways to eliminate the chance of RF interference:
Squelch
Much like a multipath situation, “tightening” the squelch on the receiver will mute the audio output when
the signal is too weak to be received. Tightening the squelch will help with force the receiver to squelch
when signal becomes too weak. (refer to page 48 for programming squelch).
Transmitter power level
As mentioned above, the RF power level can be adjusted on the LT-700 (refer to page 26 for programming
LT-700 power levels). The lower the power setting, the less range the transmitter will broadcast. Lowering the
power could help decrease the amount of interference if there are many frequencies being used in the
vicinity.
Spacing of channels
Use a Listen frequency chart (on page 61) to determine the channels frequency and space the number of
channels further from each other.
DX/Local
The receiver can be adjusted to receive only the strongest signals (refer to page 50 for DX/Local
information). A DX signal will be less sensitive because distance is the ultimate goal. For applications where
you want to minimize the distance, local mode will only search for strong signals. Local mode is much
more sensitive than DX.

10
Design Guide
Notes

11
Design Guide
Notes

15
LT-800LT-
800
LT-700
LT-700 Package Contents
• LT-700-863
• Quick Reference Card
• Warranty Card
• FM Manual Card
Listen Configurations
• LT-700-863
LT-700 User’s Manual Table of Contents
Specifications 17
Block Diagram 18
Quick Reference 19
Setup Instructions 20
Operating Instructions 23
Programming Instructions 25
Accessories 28
Notes 29
LT-700-863
Portable Display FM
Transmitter (863 MHz)