Listen Technologies LT- 800-072 - Manual (Page 18)

14
Channel Selection Setup InstructionsQuick Reference
Speci
fi cations
Package Contents Package Contents Channel Selection
It is important to choose channels that are free from interference to
achieve proper operation of your Listen equipment. This process is trial
and error. Before turning on the transmitter, listen to the wide band
channels on the receivers (lettered channels at 72 MHz and channels
that start with a “2” for 216 MHz when using a Listen receiver). Listen to
the audio through the headphone or via the speaker and choose a
channel with the least amount of interference. Unless you are
interfacing with an existing narrowband transmission system, always
use a wide band channel.
If you are using multiple channels follow this process:
1. Same Space If you are using multiple transmitters in the same space,
the highest number of channels that will work simultaneously is six at
72 MHz and three at 216 MHz. With all of the transmitters
off, listen for interference on all the wide band channels with a
Listen receiver. Using the frequency compatibility tables on pages
15-17, eliminate any channels that have noticeable interference.
Now choose the channels with the widest channel spacing. It is
recommended that adjacent channels be spaced at least 300k Hz
apart. If there is no interference the following channels are
recommended. For a 72 MHz system, use channels A, C, E, I, J
and H. For a 216 MHz system, use channels 2A, 2K and 2V.
2. Distributed Spacing If you are using transmitters that are distributed
over a large area, you can achieve more simultaneous broadcast
channels. However, it is critical that your receiver(s) be located as
close to its transmitter as possible. You can use adjacent channels
(see frequency compatibility tables (on pages 15-17) in this case
as long as the adjacent channel transmitter is at least 50% further
away from the receiver than the original transmitter. Example: The
transmitter for the receiver on channel E is 100 feet from the
receiver. The adjacent channel transmitter on channel D should
be at least 150 feet away.
It is highly recommended that after channel selection has been
achieved, you lock the channel so that it cannot be changed by the
user. To accomplish LOCK on the LT-800, press the “UP” button for 3
seconds. Repeat the process to unlock.
Notes in regard to using 72 MHz and 216 MHz systems:
1. 72 MHz is a secondary frequency band. This means that other
transmitters are licensed to use these frequencies. Thus, you may
experience interference from paging transmitters and other types
of transmissions. You will need to find a clear channel by listening
to all the wide band channels.
2. 216 MHz is a primary frequency band and no other types of
transmissions are authorized to use it. Thus, you will find the
highest probability of clear channels in this band. However, you
may experience intermodulation of the TV Channel 13 aural carrier
if there is a channel 13 transmitter in your area and you are close
to the transmitter. If you cannot find a clear channel in 216 MHz
band due to channel 13, it is recommended that you switch to
a 72 MHz system.
Channel Selection
Wide Band Recommendation
Listen recommends that you always
use a wide band channel unless you
need to be compatible with existing
narrow band receivers from other
manufacturers. Wide band channels
have lower noise than their narrow
band counterparts.
At 72MHz
The LT-800 at 72 MHz operates on 17
wide band channels and 40 narrow
band channels.
• Letters= Wide Band Channels
(Example: E)
• Numbers= Narrow Band Channels
(Example: 32)
At 216MHz
The LT-800 at 216 MHz operates on
19 wide band channels and 38 nar-
row band channels.
• “2” as left digit= Wide Band
Channel
(Example: 2C)
• “1” and “3” as left digits= Narrow
Band Channels (Examples: 1A; 3R)