Listen Portable fm 863 Mhz Assembly instructions
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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 Portable FM Transmitter
Specications 17
Block Diagram 18
Quick Reference 19
Setup Instructions 20
Operating Instructions 23
Programming Instructions 25
Accessories 28
Notes 29
LR-400/500 FM Receivers
Specications 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 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, 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. This section of the manual will help you design a system that will get the best range with the least
amount of interference.
Audio Source
FM Transmitter Receiver
When designing an FM system it is important to keep the following in mind:
• Multipath
Multipath distortion is a form of RF interference that occurs when radio signals have more than one path between
the receiver and the transmitter. This could occur in rooms with metallic or other RF-reective surfaces, such as
furniture, walls, or coated glass. 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).
Design Guide
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 line cable 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
1/8”Phone Wiring
+ Tip
+ Ring
-
- Sleeve
Unbalanced
Mic input
Line input
LR-500
Portable Programmable
Display FM Receiver (863 MHz)
LR-400
Portable Display FM
Receiver (863 MHz)
LT-700
Portable Display FM
Transmitter (863 MHz)
7
Design Guide
System Overview
Listen offers two different portable receivers.
Receivers
LR-500
Portable Programmable
Display FM Receiver (863 MHz)
LR-400
Portable Display FM
Receiver (863 MHz)
The LT-700 modulates the audio on an FM carrier and transmits the signal via an antenna
on the unit.
Transmitter
LT-700
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 – 100 ft
P2 – 150 ft
P3 – 200 ft
Range varries depending on enviroment.
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 nd 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 nd 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 nd these channels.
If the receiver nds 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 channels frequency and space the number of channels further from
each other.
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. “Tightening” the squelch will turn
the receiver off if it is chattering because of multipath (refer to page 48 for programming squelch).
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 keep the
receivers closer to the transmitter.
Multiple Portable Systems
In many 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. Without squelch you would hear radio noise in your earphone. Tightening the squelch will
help with keeping the receiver tuned to the nearest transmitter (refer to page 48 for programming squelch).
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 keep the
receivers closer to the transmitter.
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).
10
Design Guide
Notes
11
Design Guide
Notes
Table of contents
